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SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Mon Aug 26 2024 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH DAKOTA...EXTREME NORTHERN NEBRASKA...MINNESOTA...AND WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AND ACROSS PORTIONS OF NEW ENGLAND... ...SUMMARY... Severe thunderstorm gusts, large to very large hail and a few tornadoes are possible today and tonight across parts of South Dakota, extreme northern Nebraska, Minnesota, and Wisconsin. ...Synopsis... In mid/upper levels, a persistent and large anticyclone has shifted its center across the southern Plains to the lower Missouri Valley, with ridging northeastward across the Lake Superior and James Bay regions. The ridge will shift eastward across the Upper Great Lakes and southern QC through the period. This will occur in response to these developments on either side: 1. A broad but not very intense cyclone -- initially centered near the western ME/QC border -- will pivot roughly eastward to the adjoining parts and the Canadian Maritimes through the period. As this occurs, a shortwave trough/vorticity lobe -- now in the western semicircle of the cyclone over the St. Lawrence Valley -- should dig southward across eastern NY and extreme western New England today, then weaken and move offshore from the southern New England Coast tonight. 2. A strong shortwave trough -- initially over western MT, southeastern ID and northern UT -- should move to eastern MT and central WY by 00Z, then to the western Dakotas within 12 more hours. This will foster the northeastward ejection of two weak perturbations, now apparent in moisture-channel imagery over the western NE Panhandle/southeastern WY region into southwestern SD, the other over central/eastern CO. By 00Z, these features should reach eastern ND and eastern/southern SD, respectively. At the surface, 11Z analysis showed a low near FSD, with cold front arching southwestward across the NE Sandhills then northwestward to another low over east-central WY near CPR. A quasistationary frontal zone was drawn from the low northeastward over western/ northern MN. The low should move slowly eastward today while the poleward frontal extension moves little, and the cold front moves southeastward into northwestern IA and eastern/central NE. The western segment of that front should hang up over northwestern NE and east-central WY amid mass response to the approaching shortwave trough, which also should induce a surface trough and perhaps secondary/reinforcing baroclinic zone across the lee of the north-central Rockies over eastern WY and into southeastern MT. ...North-central Plains to Upper Midwest... Two main rounds of severe-thunderstorm potential are apparent today, each crossing portions of the main risk area, which represents an aggregated severe potential from both complexes. From east to west: 1. Strong-severe thunderstorms should develop over eastern SD near or north/northwest of the surface low this afternoon -- perhaps arising as early and far west as central SD during midday. This activity will be related to maximized low-level lift associated with the low, and a plume of large-scale ascent preceding the weaker shortwave troughs, and already supporting convection at this time over western SD. Whether the ongoing convection will be continuous with later activity is uncertain. In either event, this eastern complex should intensify substantially over the southeastern SD/southwestern MN/northwestern IA vicinity as it crosses the low-level baroclinic zone and encounters a strongly unstable, richly moist boundary layer, with upper 60s to mid 70s surface dewpoints. Beneath steep lower-middle-level lapse rates, this should contribute to a corridor of 3500-5000 J/kg MLCAPE near I-90 from the FSD area to near the Mississippi River, decreasing to a still-favorable 2000-4000 J/kg in central MN. Supercells with destructive hail, potentially significant-severe gusts, and a few tornadoes are possible, though so is fairly quick upscale expansion. 2. An area of convection may develop as early as late morning to midday well behind the surface cold front, in higher terrain of northern/central WY, initially with a marginal severe threat. This convection should be supported by at least modest low/middle-level moisture, and strong cooling/destabilization aloft, related to the swath of strong large-scale DCVA/ascent immediately preceding the northern Rockies shortwave trough. This activity may be an outgrowth or extension of nonsevere thunderstorms now over extreme western WY near the Star and Hams Fork Valleys and adjacent ranges. These thunderstorms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and storm-relative/post-frontal low-level flow to the east, on the High Plains and near the Black Hills. Northeasterly to easterly flow behind the front and near the trough, beneath strengthening southwest flow aloft, will support 45-60 kt effective-shear magnitudes. Buoyancy will increase eastward as the convection -- which may already have evolve into an outflow-dominant arc by the time it gets into greater moisture east of the Black Hills -- further intensifies into the northern part of a corridor of 1500-2000 J/kg MLCAPE and still-favorable storm-relative boundary- layer flow. Some of this convection may be supercellular to the extent it can remain at least somewhat discrete, with severe wind and large to very large hail possible. With time, wind will dominate as the main threat. This activity should encounter the outflow from the other complex somewhere over southeastern SD or southern MN tonight. Mesoscale uncertainty over the positioning and strength of the outflow (and thus threat of severe to its poleward side) preclude greater unconditional probabilities at this time. Still, a focused corridor of destructive winds remains a possibility across southern parts of SD/MN, some of it potentially affecting areas struck by the first complex. ...Northeastern CONUS... Widely scattered to scattered thunderstorms should develop over portions of eastern NY and New England, as well as parts of western/central PA and northwestern MD -- each moving southward to southeastward through a favorable airmass for organized convection. Strong to locally severe gusts are possible, along with severe hail. Over the New England part of the outlook, cold air aloft, overlying low-level moisture represented by mid/upper 50s F surface dewpoints, should combine with limited diurnal heating to remove MLCINH, and support peak/preconvective MLCAPE ion the 1000-1500 J/kg range. Though low-level flow will be modest, relatively straight/lengthy hodographs will support some hail potential. Further southwest, greater low-level moisture (dewpoints mostly mid/upper 60s to near 70 F at lower elevations) but weaker mid/upper-level lapse rates will be present, yielding similar CAPE values but with different vertical distribution of buoyancy (more skewed to low levels). Still, enough deep/speed shear will be present to support organized multicells and at least transient/isolated supercells. ..Edwards/Bentley.. 08/26/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Mon Aug 26 2024 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH DAKOTA...EXTREME NORTHERN NEBRASKA...MINNESOTA...AND WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AND ACROSS PORTIONS OF NEW ENGLAND... ...SUMMARY... Severe thunderstorm gusts, large to very large hail and a few tornadoes are possible today and tonight across parts of South Dakota, extreme northern Nebraska, Minnesota, and Wisconsin. ...Synopsis... In mid/upper levels, a persistent and large anticyclone has shifted its center across the southern Plains to the lower Missouri Valley, with ridging northeastward across the Lake Superior and James Bay regions. The ridge will shift eastward across the Upper Great Lakes and southern QC through the period. This will occur in response to these developments on either side: 1. A broad but not very intense cyclone -- initially centered near the western ME/QC border -- will pivot roughly eastward to the adjoining parts and the Canadian Maritimes through the period. As this occurs, a shortwave trough/vorticity lobe -- now in the western semicircle of the cyclone over the St. Lawrence Valley -- should dig southward across eastern NY and extreme western New England today, then weaken and move offshore from the southern New England Coast tonight. 2. A strong shortwave trough -- initially over western MT, southeastern ID and northern UT -- should move to eastern MT and central WY by 00Z, then to the western Dakotas within 12 more hours. This will foster the northeastward ejection of two weak perturbations, now apparent in moisture-channel imagery over the western NE Panhandle/southeastern WY region into southwestern SD, the other over central/eastern CO. By 00Z, these features should reach eastern ND and eastern/southern SD, respectively. At the surface, 11Z analysis showed a low near FSD, with cold front arching southwestward across the NE Sandhills then northwestward to another low over east-central WY near CPR. A quasistationary frontal zone was drawn from the low northeastward over western/ northern MN. The low should move slowly eastward today while the poleward frontal extension moves little, and the cold front moves southeastward into northwestern IA and eastern/central NE. The western segment of that front should hang up over northwestern NE and east-central WY amid mass response to the approaching shortwave trough, which also should induce a surface trough and perhaps secondary/reinforcing baroclinic zone across the lee of the north-central Rockies over eastern WY and into southeastern MT. ...North-central Plains to Upper Midwest... Two main rounds of severe-thunderstorm potential are apparent today, each crossing portions of the main risk area, which represents an aggregated severe potential from both complexes. From east to west: 1. Strong-severe thunderstorms should develop over eastern SD near or north/northwest of the surface low this afternoon -- perhaps arising as early and far west as central SD during midday. This activity will be related to maximized low-level lift associated with the low, and a plume of large-scale ascent preceding the weaker shortwave troughs, and already supporting convection at this time over western SD. Whether the ongoing convection will be continuous with later activity is uncertain. In either event, this eastern complex should intensify substantially over the southeastern SD/southwestern MN/northwestern IA vicinity as it crosses the low-level baroclinic zone and encounters a strongly unstable, richly moist boundary layer, with upper 60s to mid 70s surface dewpoints. Beneath steep lower-middle-level lapse rates, this should contribute to a corridor of 3500-5000 J/kg MLCAPE near I-90 from the FSD area to near the Mississippi River, decreasing to a still-favorable 2000-4000 J/kg in central MN. Supercells with destructive hail, potentially significant-severe gusts, and a few tornadoes are possible, though so is fairly quick upscale expansion. 2. An area of convection may develop as early as late morning to midday well behind the surface cold front, in higher terrain of northern/central WY, initially with a marginal severe threat. This convection should be supported by at least modest low/middle-level moisture, and strong cooling/destabilization aloft, related to the swath of strong large-scale DCVA/ascent immediately preceding the northern Rockies shortwave trough. This activity may be an outgrowth or extension of nonsevere thunderstorms now over extreme western WY near the Star and Hams Fork Valleys and adjacent ranges. These thunderstorms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and storm-relative/post-frontal low-level flow to the east, on the High Plains and near the Black Hills. Northeasterly to easterly flow behind the front and near the trough, beneath strengthening southwest flow aloft, will support 45-60 kt effective-shear magnitudes. Buoyancy will increase eastward as the convection -- which may already have evolve into an outflow-dominant arc by the time it gets into greater moisture east of the Black Hills -- further intensifies into the northern part of a corridor of 1500-2000 J/kg MLCAPE and still-favorable storm-relative boundary- layer flow. Some of this convection may be supercellular to the extent it can remain at least somewhat discrete, with severe wind and large to very large hail possible. With time, wind will dominate as the main threat. This activity should encounter the outflow from the other complex somewhere over southeastern SD or southern MN tonight. Mesoscale uncertainty over the positioning and strength of the outflow (and thus threat of severe to its poleward side) preclude greater unconditional probabilities at this time. Still, a focused corridor of destructive winds remains a possibility across southern parts of SD/MN, some of it potentially affecting areas struck by the first complex. ...Northeastern CONUS... Widely scattered to scattered thunderstorms should develop over portions of eastern NY and New England, as well as parts of western/central PA and northwestern MD -- each moving southward to southeastward through a favorable airmass for organized convection. Strong to locally severe gusts are possible, along with severe hail. Over the New England part of the outlook, cold air aloft, overlying low-level moisture represented by mid/upper 50s F surface dewpoints, should combine with limited diurnal heating to remove MLCINH, and support peak/preconvective MLCAPE ion the 1000-1500 J/kg range. Though low-level flow will be modest, relatively straight/lengthy hodographs will support some hail potential. Further southwest, greater low-level moisture (dewpoints mostly mid/upper 60s to near 70 F at lower elevations) but weaker mid/upper-level lapse rates will be present, yielding similar CAPE values but with different vertical distribution of buoyancy (more skewed to low levels). Still, enough deep/speed shear will be present to support organized multicells and at least transient/isolated supercells. ..Edwards/Bentley.. 08/26/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Mon Aug 26 2024 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH DAKOTA...EXTREME NORTHERN NEBRASKA...MINNESOTA...AND WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AND ACROSS PORTIONS OF NEW ENGLAND... ...SUMMARY... Severe thunderstorm gusts, large to very large hail and a few tornadoes are possible today and tonight across parts of South Dakota, extreme northern Nebraska, Minnesota, and Wisconsin. ...Synopsis... In mid/upper levels, a persistent and large anticyclone has shifted its center across the southern Plains to the lower Missouri Valley, with ridging northeastward across the Lake Superior and James Bay regions. The ridge will shift eastward across the Upper Great Lakes and southern QC through the period. This will occur in response to these developments on either side: 1. A broad but not very intense cyclone -- initially centered near the western ME/QC border -- will pivot roughly eastward to the adjoining parts and the Canadian Maritimes through the period. As this occurs, a shortwave trough/vorticity lobe -- now in the western semicircle of the cyclone over the St. Lawrence Valley -- should dig southward across eastern NY and extreme western New England today, then weaken and move offshore from the southern New England Coast tonight. 2. A strong shortwave trough -- initially over western MT, southeastern ID and northern UT -- should move to eastern MT and central WY by 00Z, then to the western Dakotas within 12 more hours. This will foster the northeastward ejection of two weak perturbations, now apparent in moisture-channel imagery over the western NE Panhandle/southeastern WY region into southwestern SD, the other over central/eastern CO. By 00Z, these features should reach eastern ND and eastern/southern SD, respectively. At the surface, 11Z analysis showed a low near FSD, with cold front arching southwestward across the NE Sandhills then northwestward to another low over east-central WY near CPR. A quasistationary frontal zone was drawn from the low northeastward over western/ northern MN. The low should move slowly eastward today while the poleward frontal extension moves little, and the cold front moves southeastward into northwestern IA and eastern/central NE. The western segment of that front should hang up over northwestern NE and east-central WY amid mass response to the approaching shortwave trough, which also should induce a surface trough and perhaps secondary/reinforcing baroclinic zone across the lee of the north-central Rockies over eastern WY and into southeastern MT. ...North-central Plains to Upper Midwest... Two main rounds of severe-thunderstorm potential are apparent today, each crossing portions of the main risk area, which represents an aggregated severe potential from both complexes. From east to west: 1. Strong-severe thunderstorms should develop over eastern SD near or north/northwest of the surface low this afternoon -- perhaps arising as early and far west as central SD during midday. This activity will be related to maximized low-level lift associated with the low, and a plume of large-scale ascent preceding the weaker shortwave troughs, and already supporting convection at this time over western SD. Whether the ongoing convection will be continuous with later activity is uncertain. In either event, this eastern complex should intensify substantially over the southeastern SD/southwestern MN/northwestern IA vicinity as it crosses the low-level baroclinic zone and encounters a strongly unstable, richly moist boundary layer, with upper 60s to mid 70s surface dewpoints. Beneath steep lower-middle-level lapse rates, this should contribute to a corridor of 3500-5000 J/kg MLCAPE near I-90 from the FSD area to near the Mississippi River, decreasing to a still-favorable 2000-4000 J/kg in central MN. Supercells with destructive hail, potentially significant-severe gusts, and a few tornadoes are possible, though so is fairly quick upscale expansion. 2. An area of convection may develop as early as late morning to midday well behind the surface cold front, in higher terrain of northern/central WY, initially with a marginal severe threat. This convection should be supported by at least modest low/middle-level moisture, and strong cooling/destabilization aloft, related to the swath of strong large-scale DCVA/ascent immediately preceding the northern Rockies shortwave trough. This activity may be an outgrowth or extension of nonsevere thunderstorms now over extreme western WY near the Star and Hams Fork Valleys and adjacent ranges. These thunderstorms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and storm-relative/post-frontal low-level flow to the east, on the High Plains and near the Black Hills. Northeasterly to easterly flow behind the front and near the trough, beneath strengthening southwest flow aloft, will support 45-60 kt effective-shear magnitudes. Buoyancy will increase eastward as the convection -- which may already have evolve into an outflow-dominant arc by the time it gets into greater moisture east of the Black Hills -- further intensifies into the northern part of a corridor of 1500-2000 J/kg MLCAPE and still-favorable storm-relative boundary- layer flow. Some of this convection may be supercellular to the extent it can remain at least somewhat discrete, with severe wind and large to very large hail possible. With time, wind will dominate as the main threat. This activity should encounter the outflow from the other complex somewhere over southeastern SD or southern MN tonight. Mesoscale uncertainty over the positioning and strength of the outflow (and thus threat of severe to its poleward side) preclude greater unconditional probabilities at this time. Still, a focused corridor of destructive winds remains a possibility across southern parts of SD/MN, some of it potentially affecting areas struck by the first complex. ...Northeastern CONUS... Widely scattered to scattered thunderstorms should develop over portions of eastern NY and New England, as well as parts of western/central PA and northwestern MD -- each moving southward to southeastward through a favorable airmass for organized convection. Strong to locally severe gusts are possible, along with severe hail. Over the New England part of the outlook, cold air aloft, overlying low-level moisture represented by mid/upper 50s F surface dewpoints, should combine with limited diurnal heating to remove MLCINH, and support peak/preconvective MLCAPE ion the 1000-1500 J/kg range. Though low-level flow will be modest, relatively straight/lengthy hodographs will support some hail potential. Further southwest, greater low-level moisture (dewpoints mostly mid/upper 60s to near 70 F at lower elevations) but weaker mid/upper-level lapse rates will be present, yielding similar CAPE values but with different vertical distribution of buoyancy (more skewed to low levels). Still, enough deep/speed shear will be present to support organized multicells and at least transient/isolated supercells. ..Edwards/Bentley.. 08/26/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Mon Aug 26 2024 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH DAKOTA...EXTREME NORTHERN NEBRASKA...MINNESOTA...AND WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AND ACROSS PORTIONS OF NEW ENGLAND... ...SUMMARY... Severe thunderstorm gusts, large to very large hail and a few tornadoes are possible today and tonight across parts of South Dakota, extreme northern Nebraska, Minnesota, and Wisconsin. ...Synopsis... In mid/upper levels, a persistent and large anticyclone has shifted its center across the southern Plains to the lower Missouri Valley, with ridging northeastward across the Lake Superior and James Bay regions. The ridge will shift eastward across the Upper Great Lakes and southern QC through the period. This will occur in response to these developments on either side: 1. A broad but not very intense cyclone -- initially centered near the western ME/QC border -- will pivot roughly eastward to the adjoining parts and the Canadian Maritimes through the period. As this occurs, a shortwave trough/vorticity lobe -- now in the western semicircle of the cyclone over the St. Lawrence Valley -- should dig southward across eastern NY and extreme western New England today, then weaken and move offshore from the southern New England Coast tonight. 2. A strong shortwave trough -- initially over western MT, southeastern ID and northern UT -- should move to eastern MT and central WY by 00Z, then to the western Dakotas within 12 more hours. This will foster the northeastward ejection of two weak perturbations, now apparent in moisture-channel imagery over the western NE Panhandle/southeastern WY region into southwestern SD, the other over central/eastern CO. By 00Z, these features should reach eastern ND and eastern/southern SD, respectively. At the surface, 11Z analysis showed a low near FSD, with cold front arching southwestward across the NE Sandhills then northwestward to another low over east-central WY near CPR. A quasistationary frontal zone was drawn from the low northeastward over western/ northern MN. The low should move slowly eastward today while the poleward frontal extension moves little, and the cold front moves southeastward into northwestern IA and eastern/central NE. The western segment of that front should hang up over northwestern NE and east-central WY amid mass response to the approaching shortwave trough, which also should induce a surface trough and perhaps secondary/reinforcing baroclinic zone across the lee of the north-central Rockies over eastern WY and into southeastern MT. ...North-central Plains to Upper Midwest... Two main rounds of severe-thunderstorm potential are apparent today, each crossing portions of the main risk area, which represents an aggregated severe potential from both complexes. From east to west: 1. Strong-severe thunderstorms should develop over eastern SD near or north/northwest of the surface low this afternoon -- perhaps arising as early and far west as central SD during midday. This activity will be related to maximized low-level lift associated with the low, and a plume of large-scale ascent preceding the weaker shortwave troughs, and already supporting convection at this time over western SD. Whether the ongoing convection will be continuous with later activity is uncertain. In either event, this eastern complex should intensify substantially over the southeastern SD/southwestern MN/northwestern IA vicinity as it crosses the low-level baroclinic zone and encounters a strongly unstable, richly moist boundary layer, with upper 60s to mid 70s surface dewpoints. Beneath steep lower-middle-level lapse rates, this should contribute to a corridor of 3500-5000 J/kg MLCAPE near I-90 from the FSD area to near the Mississippi River, decreasing to a still-favorable 2000-4000 J/kg in central MN. Supercells with destructive hail, potentially significant-severe gusts, and a few tornadoes are possible, though so is fairly quick upscale expansion. 2. An area of convection may develop as early as late morning to midday well behind the surface cold front, in higher terrain of northern/central WY, initially with a marginal severe threat. This convection should be supported by at least modest low/middle-level moisture, and strong cooling/destabilization aloft, related to the swath of strong large-scale DCVA/ascent immediately preceding the northern Rockies shortwave trough. This activity may be an outgrowth or extension of nonsevere thunderstorms now over extreme western WY near the Star and Hams Fork Valleys and adjacent ranges. These thunderstorms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and storm-relative/post-frontal low-level flow to the east, on the High Plains and near the Black Hills. Northeasterly to easterly flow behind the front and near the trough, beneath strengthening southwest flow aloft, will support 45-60 kt effective-shear magnitudes. Buoyancy will increase eastward as the convection -- which may already have evolve into an outflow-dominant arc by the time it gets into greater moisture east of the Black Hills -- further intensifies into the northern part of a corridor of 1500-2000 J/kg MLCAPE and still-favorable storm-relative boundary- layer flow. Some of this convection may be supercellular to the extent it can remain at least somewhat discrete, with severe wind and large to very large hail possible. With time, wind will dominate as the main threat. This activity should encounter the outflow from the other complex somewhere over southeastern SD or southern MN tonight. Mesoscale uncertainty over the positioning and strength of the outflow (and thus threat of severe to its poleward side) preclude greater unconditional probabilities at this time. Still, a focused corridor of destructive winds remains a possibility across southern parts of SD/MN, some of it potentially affecting areas struck by the first complex. ...Northeastern CONUS... Widely scattered to scattered thunderstorms should develop over portions of eastern NY and New England, as well as parts of western/central PA and northwestern MD -- each moving southward to southeastward through a favorable airmass for organized convection. Strong to locally severe gusts are possible, along with severe hail. Over the New England part of the outlook, cold air aloft, overlying low-level moisture represented by mid/upper 50s F surface dewpoints, should combine with limited diurnal heating to remove MLCINH, and support peak/preconvective MLCAPE ion the 1000-1500 J/kg range. Though low-level flow will be modest, relatively straight/lengthy hodographs will support some hail potential. Further southwest, greater low-level moisture (dewpoints mostly mid/upper 60s to near 70 F at lower elevations) but weaker mid/upper-level lapse rates will be present, yielding similar CAPE values but with different vertical distribution of buoyancy (more skewed to low levels). Still, enough deep/speed shear will be present to support organized multicells and at least transient/isolated supercells. ..Edwards/Bentley.. 08/26/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Mon Aug 26 2024 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH DAKOTA...EXTREME NORTHERN NEBRASKA...MINNESOTA...AND WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AND ACROSS PORTIONS OF NEW ENGLAND... ...SUMMARY... Severe thunderstorm gusts, large to very large hail and a few tornadoes are possible today and tonight across parts of South Dakota, extreme northern Nebraska, Minnesota, and Wisconsin. ...Synopsis... In mid/upper levels, a persistent and large anticyclone has shifted its center across the southern Plains to the lower Missouri Valley, with ridging northeastward across the Lake Superior and James Bay regions. The ridge will shift eastward across the Upper Great Lakes and southern QC through the period. This will occur in response to these developments on either side: 1. A broad but not very intense cyclone -- initially centered near the western ME/QC border -- will pivot roughly eastward to the adjoining parts and the Canadian Maritimes through the period. As this occurs, a shortwave trough/vorticity lobe -- now in the western semicircle of the cyclone over the St. Lawrence Valley -- should dig southward across eastern NY and extreme western New England today, then weaken and move offshore from the southern New England Coast tonight. 2. A strong shortwave trough -- initially over western MT, southeastern ID and northern UT -- should move to eastern MT and central WY by 00Z, then to the western Dakotas within 12 more hours. This will foster the northeastward ejection of two weak perturbations, now apparent in moisture-channel imagery over the western NE Panhandle/southeastern WY region into southwestern SD, the other over central/eastern CO. By 00Z, these features should reach eastern ND and eastern/southern SD, respectively. At the surface, 11Z analysis showed a low near FSD, with cold front arching southwestward across the NE Sandhills then northwestward to another low over east-central WY near CPR. A quasistationary frontal zone was drawn from the low northeastward over western/ northern MN. The low should move slowly eastward today while the poleward frontal extension moves little, and the cold front moves southeastward into northwestern IA and eastern/central NE. The western segment of that front should hang up over northwestern NE and east-central WY amid mass response to the approaching shortwave trough, which also should induce a surface trough and perhaps secondary/reinforcing baroclinic zone across the lee of the north-central Rockies over eastern WY and into southeastern MT. ...North-central Plains to Upper Midwest... Two main rounds of severe-thunderstorm potential are apparent today, each crossing portions of the main risk area, which represents an aggregated severe potential from both complexes. From east to west: 1. Strong-severe thunderstorms should develop over eastern SD near or north/northwest of the surface low this afternoon -- perhaps arising as early and far west as central SD during midday. This activity will be related to maximized low-level lift associated with the low, and a plume of large-scale ascent preceding the weaker shortwave troughs, and already supporting convection at this time over western SD. Whether the ongoing convection will be continuous with later activity is uncertain. In either event, this eastern complex should intensify substantially over the southeastern SD/southwestern MN/northwestern IA vicinity as it crosses the low-level baroclinic zone and encounters a strongly unstable, richly moist boundary layer, with upper 60s to mid 70s surface dewpoints. Beneath steep lower-middle-level lapse rates, this should contribute to a corridor of 3500-5000 J/kg MLCAPE near I-90 from the FSD area to near the Mississippi River, decreasing to a still-favorable 2000-4000 J/kg in central MN. Supercells with destructive hail, potentially significant-severe gusts, and a few tornadoes are possible, though so is fairly quick upscale expansion. 2. An area of convection may develop as early as late morning to midday well behind the surface cold front, in higher terrain of northern/central WY, initially with a marginal severe threat. This convection should be supported by at least modest low/middle-level moisture, and strong cooling/destabilization aloft, related to the swath of strong large-scale DCVA/ascent immediately preceding the northern Rockies shortwave trough. This activity may be an outgrowth or extension of nonsevere thunderstorms now over extreme western WY near the Star and Hams Fork Valleys and adjacent ranges. These thunderstorms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and storm-relative/post-frontal low-level flow to the east, on the High Plains and near the Black Hills. Northeasterly to easterly flow behind the front and near the trough, beneath strengthening southwest flow aloft, will support 45-60 kt effective-shear magnitudes. Buoyancy will increase eastward as the convection -- which may already have evolve into an outflow-dominant arc by the time it gets into greater moisture east of the Black Hills -- further intensifies into the northern part of a corridor of 1500-2000 J/kg MLCAPE and still-favorable storm-relative boundary- layer flow. Some of this convection may be supercellular to the extent it can remain at least somewhat discrete, with severe wind and large to very large hail possible. With time, wind will dominate as the main threat. This activity should encounter the outflow from the other complex somewhere over southeastern SD or southern MN tonight. Mesoscale uncertainty over the positioning and strength of the outflow (and thus threat of severe to its poleward side) preclude greater unconditional probabilities at this time. Still, a focused corridor of destructive winds remains a possibility across southern parts of SD/MN, some of it potentially affecting areas struck by the first complex. ...Northeastern CONUS... Widely scattered to scattered thunderstorms should develop over portions of eastern NY and New England, as well as parts of western/central PA and northwestern MD -- each moving southward to southeastward through a favorable airmass for organized convection. Strong to locally severe gusts are possible, along with severe hail. Over the New England part of the outlook, cold air aloft, overlying low-level moisture represented by mid/upper 50s F surface dewpoints, should combine with limited diurnal heating to remove MLCINH, and support peak/preconvective MLCAPE ion the 1000-1500 J/kg range. Though low-level flow will be modest, relatively straight/lengthy hodographs will support some hail potential. Further southwest, greater low-level moisture (dewpoints mostly mid/upper 60s to near 70 F at lower elevations) but weaker mid/upper-level lapse rates will be present, yielding similar CAPE values but with different vertical distribution of buoyancy (more skewed to low levels). Still, enough deep/speed shear will be present to support organized multicells and at least transient/isolated supercells. ..Edwards/Bentley.. 08/26/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Mon Aug 26 2024 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH DAKOTA...EXTREME NORTHERN NEBRASKA...MINNESOTA...AND WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AND ACROSS PORTIONS OF NEW ENGLAND... ...SUMMARY... Severe thunderstorm gusts, large to very large hail and a few tornadoes are possible today and tonight across parts of South Dakota, extreme northern Nebraska, Minnesota, and Wisconsin. ...Synopsis... In mid/upper levels, a persistent and large anticyclone has shifted its center across the southern Plains to the lower Missouri Valley, with ridging northeastward across the Lake Superior and James Bay regions. The ridge will shift eastward across the Upper Great Lakes and southern QC through the period. This will occur in response to these developments on either side: 1. A broad but not very intense cyclone -- initially centered near the western ME/QC border -- will pivot roughly eastward to the adjoining parts and the Canadian Maritimes through the period. As this occurs, a shortwave trough/vorticity lobe -- now in the western semicircle of the cyclone over the St. Lawrence Valley -- should dig southward across eastern NY and extreme western New England today, then weaken and move offshore from the southern New England Coast tonight. 2. A strong shortwave trough -- initially over western MT, southeastern ID and northern UT -- should move to eastern MT and central WY by 00Z, then to the western Dakotas within 12 more hours. This will foster the northeastward ejection of two weak perturbations, now apparent in moisture-channel imagery over the western NE Panhandle/southeastern WY region into southwestern SD, the other over central/eastern CO. By 00Z, these features should reach eastern ND and eastern/southern SD, respectively. At the surface, 11Z analysis showed a low near FSD, with cold front arching southwestward across the NE Sandhills then northwestward to another low over east-central WY near CPR. A quasistationary frontal zone was drawn from the low northeastward over western/ northern MN. The low should move slowly eastward today while the poleward frontal extension moves little, and the cold front moves southeastward into northwestern IA and eastern/central NE. The western segment of that front should hang up over northwestern NE and east-central WY amid mass response to the approaching shortwave trough, which also should induce a surface trough and perhaps secondary/reinforcing baroclinic zone across the lee of the north-central Rockies over eastern WY and into southeastern MT. ...North-central Plains to Upper Midwest... Two main rounds of severe-thunderstorm potential are apparent today, each crossing portions of the main risk area, which represents an aggregated severe potential from both complexes. From east to west: 1. Strong-severe thunderstorms should develop over eastern SD near or north/northwest of the surface low this afternoon -- perhaps arising as early and far west as central SD during midday. This activity will be related to maximized low-level lift associated with the low, and a plume of large-scale ascent preceding the weaker shortwave troughs, and already supporting convection at this time over western SD. Whether the ongoing convection will be continuous with later activity is uncertain. In either event, this eastern complex should intensify substantially over the southeastern SD/southwestern MN/northwestern IA vicinity as it crosses the low-level baroclinic zone and encounters a strongly unstable, richly moist boundary layer, with upper 60s to mid 70s surface dewpoints. Beneath steep lower-middle-level lapse rates, this should contribute to a corridor of 3500-5000 J/kg MLCAPE near I-90 from the FSD area to near the Mississippi River, decreasing to a still-favorable 2000-4000 J/kg in central MN. Supercells with destructive hail, potentially significant-severe gusts, and a few tornadoes are possible, though so is fairly quick upscale expansion. 2. An area of convection may develop as early as late morning to midday well behind the surface cold front, in higher terrain of northern/central WY, initially with a marginal severe threat. This convection should be supported by at least modest low/middle-level moisture, and strong cooling/destabilization aloft, related to the swath of strong large-scale DCVA/ascent immediately preceding the northern Rockies shortwave trough. This activity may be an outgrowth or extension of nonsevere thunderstorms now over extreme western WY near the Star and Hams Fork Valleys and adjacent ranges. These thunderstorms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and storm-relative/post-frontal low-level flow to the east, on the High Plains and near the Black Hills. Northeasterly to easterly flow behind the front and near the trough, beneath strengthening southwest flow aloft, will support 45-60 kt effective-shear magnitudes. Buoyancy will increase eastward as the convection -- which may already have evolve into an outflow-dominant arc by the time it gets into greater moisture east of the Black Hills -- further intensifies into the northern part of a corridor of 1500-2000 J/kg MLCAPE and still-favorable storm-relative boundary- layer flow. Some of this convection may be supercellular to the extent it can remain at least somewhat discrete, with severe wind and large to very large hail possible. With time, wind will dominate as the main threat. This activity should encounter the outflow from the other complex somewhere over southeastern SD or southern MN tonight. Mesoscale uncertainty over the positioning and strength of the outflow (and thus threat of severe to its poleward side) preclude greater unconditional probabilities at this time. Still, a focused corridor of destructive winds remains a possibility across southern parts of SD/MN, some of it potentially affecting areas struck by the first complex. ...Northeastern CONUS... Widely scattered to scattered thunderstorms should develop over portions of eastern NY and New England, as well as parts of western/central PA and northwestern MD -- each moving southward to southeastward through a favorable airmass for organized convection. Strong to locally severe gusts are possible, along with severe hail. Over the New England part of the outlook, cold air aloft, overlying low-level moisture represented by mid/upper 50s F surface dewpoints, should combine with limited diurnal heating to remove MLCINH, and support peak/preconvective MLCAPE ion the 1000-1500 J/kg range. Though low-level flow will be modest, relatively straight/lengthy hodographs will support some hail potential. Further southwest, greater low-level moisture (dewpoints mostly mid/upper 60s to near 70 F at lower elevations) but weaker mid/upper-level lapse rates will be present, yielding similar CAPE values but with different vertical distribution of buoyancy (more skewed to low levels). Still, enough deep/speed shear will be present to support organized multicells and at least transient/isolated supercells. ..Edwards/Bentley.. 08/26/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Mon Aug 26 2024 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH DAKOTA...EXTREME NORTHERN NEBRASKA...MINNESOTA...AND WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AND ACROSS PORTIONS OF NEW ENGLAND... ...SUMMARY... Severe thunderstorm gusts, large to very large hail and a few tornadoes are possible today and tonight across parts of South Dakota, extreme northern Nebraska, Minnesota, and Wisconsin. ...Synopsis... In mid/upper levels, a persistent and large anticyclone has shifted its center across the southern Plains to the lower Missouri Valley, with ridging northeastward across the Lake Superior and James Bay regions. The ridge will shift eastward across the Upper Great Lakes and southern QC through the period. This will occur in response to these developments on either side: 1. A broad but not very intense cyclone -- initially centered near the western ME/QC border -- will pivot roughly eastward to the adjoining parts and the Canadian Maritimes through the period. As this occurs, a shortwave trough/vorticity lobe -- now in the western semicircle of the cyclone over the St. Lawrence Valley -- should dig southward across eastern NY and extreme western New England today, then weaken and move offshore from the southern New England Coast tonight. 2. A strong shortwave trough -- initially over western MT, southeastern ID and northern UT -- should move to eastern MT and central WY by 00Z, then to the western Dakotas within 12 more hours. This will foster the northeastward ejection of two weak perturbations, now apparent in moisture-channel imagery over the western NE Panhandle/southeastern WY region into southwestern SD, the other over central/eastern CO. By 00Z, these features should reach eastern ND and eastern/southern SD, respectively. At the surface, 11Z analysis showed a low near FSD, with cold front arching southwestward across the NE Sandhills then northwestward to another low over east-central WY near CPR. A quasistationary frontal zone was drawn from the low northeastward over western/ northern MN. The low should move slowly eastward today while the poleward frontal extension moves little, and the cold front moves southeastward into northwestern IA and eastern/central NE. The western segment of that front should hang up over northwestern NE and east-central WY amid mass response to the approaching shortwave trough, which also should induce a surface trough and perhaps secondary/reinforcing baroclinic zone across the lee of the north-central Rockies over eastern WY and into southeastern MT. ...North-central Plains to Upper Midwest... Two main rounds of severe-thunderstorm potential are apparent today, each crossing portions of the main risk area, which represents an aggregated severe potential from both complexes. From east to west: 1. Strong-severe thunderstorms should develop over eastern SD near or north/northwest of the surface low this afternoon -- perhaps arising as early and far west as central SD during midday. This activity will be related to maximized low-level lift associated with the low, and a plume of large-scale ascent preceding the weaker shortwave troughs, and already supporting convection at this time over western SD. Whether the ongoing convection will be continuous with later activity is uncertain. In either event, this eastern complex should intensify substantially over the southeastern SD/southwestern MN/northwestern IA vicinity as it crosses the low-level baroclinic zone and encounters a strongly unstable, richly moist boundary layer, with upper 60s to mid 70s surface dewpoints. Beneath steep lower-middle-level lapse rates, this should contribute to a corridor of 3500-5000 J/kg MLCAPE near I-90 from the FSD area to near the Mississippi River, decreasing to a still-favorable 2000-4000 J/kg in central MN. Supercells with destructive hail, potentially significant-severe gusts, and a few tornadoes are possible, though so is fairly quick upscale expansion. 2. An area of convection may develop as early as late morning to midday well behind the surface cold front, in higher terrain of northern/central WY, initially with a marginal severe threat. This convection should be supported by at least modest low/middle-level moisture, and strong cooling/destabilization aloft, related to the swath of strong large-scale DCVA/ascent immediately preceding the northern Rockies shortwave trough. This activity may be an outgrowth or extension of nonsevere thunderstorms now over extreme western WY near the Star and Hams Fork Valleys and adjacent ranges. These thunderstorms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and storm-relative/post-frontal low-level flow to the east, on the High Plains and near the Black Hills. Northeasterly to easterly flow behind the front and near the trough, beneath strengthening southwest flow aloft, will support 45-60 kt effective-shear magnitudes. Buoyancy will increase eastward as the convection -- which may already have evolve into an outflow-dominant arc by the time it gets into greater moisture east of the Black Hills -- further intensifies into the northern part of a corridor of 1500-2000 J/kg MLCAPE and still-favorable storm-relative boundary- layer flow. Some of this convection may be supercellular to the extent it can remain at least somewhat discrete, with severe wind and large to very large hail possible. With time, wind will dominate as the main threat. This activity should encounter the outflow from the other complex somewhere over southeastern SD or southern MN tonight. Mesoscale uncertainty over the positioning and strength of the outflow (and thus threat of severe to its poleward side) preclude greater unconditional probabilities at this time. Still, a focused corridor of destructive winds remains a possibility across southern parts of SD/MN, some of it potentially affecting areas struck by the first complex. ...Northeastern CONUS... Widely scattered to scattered thunderstorms should develop over portions of eastern NY and New England, as well as parts of western/central PA and northwestern MD -- each moving southward to southeastward through a favorable airmass for organized convection. Strong to locally severe gusts are possible, along with severe hail. Over the New England part of the outlook, cold air aloft, overlying low-level moisture represented by mid/upper 50s F surface dewpoints, should combine with limited diurnal heating to remove MLCINH, and support peak/preconvective MLCAPE ion the 1000-1500 J/kg range. Though low-level flow will be modest, relatively straight/lengthy hodographs will support some hail potential. Further southwest, greater low-level moisture (dewpoints mostly mid/upper 60s to near 70 F at lower elevations) but weaker mid/upper-level lapse rates will be present, yielding similar CAPE values but with different vertical distribution of buoyancy (more skewed to low levels). Still, enough deep/speed shear will be present to support organized multicells and at least transient/isolated supercells. ..Edwards/Bentley.. 08/26/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Mon Aug 26 2024 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH DAKOTA...EXTREME NORTHERN NEBRASKA...MINNESOTA...AND WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AND ACROSS PORTIONS OF NEW ENGLAND... ...SUMMARY... Severe thunderstorm gusts, large to very large hail and a few tornadoes are possible today and tonight across parts of South Dakota, extreme northern Nebraska, Minnesota, and Wisconsin. ...Synopsis... In mid/upper levels, a persistent and large anticyclone has shifted its center across the southern Plains to the lower Missouri Valley, with ridging northeastward across the Lake Superior and James Bay regions. The ridge will shift eastward across the Upper Great Lakes and southern QC through the period. This will occur in response to these developments on either side: 1. A broad but not very intense cyclone -- initially centered near the western ME/QC border -- will pivot roughly eastward to the adjoining parts and the Canadian Maritimes through the period. As this occurs, a shortwave trough/vorticity lobe -- now in the western semicircle of the cyclone over the St. Lawrence Valley -- should dig southward across eastern NY and extreme western New England today, then weaken and move offshore from the southern New England Coast tonight. 2. A strong shortwave trough -- initially over western MT, southeastern ID and northern UT -- should move to eastern MT and central WY by 00Z, then to the western Dakotas within 12 more hours. This will foster the northeastward ejection of two weak perturbations, now apparent in moisture-channel imagery over the western NE Panhandle/southeastern WY region into southwestern SD, the other over central/eastern CO. By 00Z, these features should reach eastern ND and eastern/southern SD, respectively. At the surface, 11Z analysis showed a low near FSD, with cold front arching southwestward across the NE Sandhills then northwestward to another low over east-central WY near CPR. A quasistationary frontal zone was drawn from the low northeastward over western/ northern MN. The low should move slowly eastward today while the poleward frontal extension moves little, and the cold front moves southeastward into northwestern IA and eastern/central NE. The western segment of that front should hang up over northwestern NE and east-central WY amid mass response to the approaching shortwave trough, which also should induce a surface trough and perhaps secondary/reinforcing baroclinic zone across the lee of the north-central Rockies over eastern WY and into southeastern MT. ...North-central Plains to Upper Midwest... Two main rounds of severe-thunderstorm potential are apparent today, each crossing portions of the main risk area, which represents an aggregated severe potential from both complexes. From east to west: 1. Strong-severe thunderstorms should develop over eastern SD near or north/northwest of the surface low this afternoon -- perhaps arising as early and far west as central SD during midday. This activity will be related to maximized low-level lift associated with the low, and a plume of large-scale ascent preceding the weaker shortwave troughs, and already supporting convection at this time over western SD. Whether the ongoing convection will be continuous with later activity is uncertain. In either event, this eastern complex should intensify substantially over the southeastern SD/southwestern MN/northwestern IA vicinity as it crosses the low-level baroclinic zone and encounters a strongly unstable, richly moist boundary layer, with upper 60s to mid 70s surface dewpoints. Beneath steep lower-middle-level lapse rates, this should contribute to a corridor of 3500-5000 J/kg MLCAPE near I-90 from the FSD area to near the Mississippi River, decreasing to a still-favorable 2000-4000 J/kg in central MN. Supercells with destructive hail, potentially significant-severe gusts, and a few tornadoes are possible, though so is fairly quick upscale expansion. 2. An area of convection may develop as early as late morning to midday well behind the surface cold front, in higher terrain of northern/central WY, initially with a marginal severe threat. This convection should be supported by at least modest low/middle-level moisture, and strong cooling/destabilization aloft, related to the swath of strong large-scale DCVA/ascent immediately preceding the northern Rockies shortwave trough. This activity may be an outgrowth or extension of nonsevere thunderstorms now over extreme western WY near the Star and Hams Fork Valleys and adjacent ranges. These thunderstorms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and storm-relative/post-frontal low-level flow to the east, on the High Plains and near the Black Hills. Northeasterly to easterly flow behind the front and near the trough, beneath strengthening southwest flow aloft, will support 45-60 kt effective-shear magnitudes. Buoyancy will increase eastward as the convection -- which may already have evolve into an outflow-dominant arc by the time it gets into greater moisture east of the Black Hills -- further intensifies into the northern part of a corridor of 1500-2000 J/kg MLCAPE and still-favorable storm-relative boundary- layer flow. Some of this convection may be supercellular to the extent it can remain at least somewhat discrete, with severe wind and large to very large hail possible. With time, wind will dominate as the main threat. This activity should encounter the outflow from the other complex somewhere over southeastern SD or southern MN tonight. Mesoscale uncertainty over the positioning and strength of the outflow (and thus threat of severe to its poleward side) preclude greater unconditional probabilities at this time. Still, a focused corridor of destructive winds remains a possibility across southern parts of SD/MN, some of it potentially affecting areas struck by the first complex. ...Northeastern CONUS... Widely scattered to scattered thunderstorms should develop over portions of eastern NY and New England, as well as parts of western/central PA and northwestern MD -- each moving southward to southeastward through a favorable airmass for organized convection. Strong to locally severe gusts are possible, along with severe hail. Over the New England part of the outlook, cold air aloft, overlying low-level moisture represented by mid/upper 50s F surface dewpoints, should combine with limited diurnal heating to remove MLCINH, and support peak/preconvective MLCAPE ion the 1000-1500 J/kg range. Though low-level flow will be modest, relatively straight/lengthy hodographs will support some hail potential. Further southwest, greater low-level moisture (dewpoints mostly mid/upper 60s to near 70 F at lower elevations) but weaker mid/upper-level lapse rates will be present, yielding similar CAPE values but with different vertical distribution of buoyancy (more skewed to low levels). Still, enough deep/speed shear will be present to support organized multicells and at least transient/isolated supercells. ..Edwards/Bentley.. 08/26/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0758 AM CDT Mon Aug 26 2024 Valid 261300Z - 271200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF SOUTH DAKOTA...EXTREME NORTHERN NEBRASKA...MINNESOTA...AND WISCONSIN... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SURROUNDING THE ENHANCED RISK...AND ACROSS PORTIONS OF NEW ENGLAND... ...SUMMARY... Severe thunderstorm gusts, large to very large hail and a few tornadoes are possible today and tonight across parts of South Dakota, extreme northern Nebraska, Minnesota, and Wisconsin. ...Synopsis... In mid/upper levels, a persistent and large anticyclone has shifted its center across the southern Plains to the lower Missouri Valley, with ridging northeastward across the Lake Superior and James Bay regions. The ridge will shift eastward across the Upper Great Lakes and southern QC through the period. This will occur in response to these developments on either side: 1. A broad but not very intense cyclone -- initially centered near the western ME/QC border -- will pivot roughly eastward to the adjoining parts and the Canadian Maritimes through the period. As this occurs, a shortwave trough/vorticity lobe -- now in the western semicircle of the cyclone over the St. Lawrence Valley -- should dig southward across eastern NY and extreme western New England today, then weaken and move offshore from the southern New England Coast tonight. 2. A strong shortwave trough -- initially over western MT, southeastern ID and northern UT -- should move to eastern MT and central WY by 00Z, then to the western Dakotas within 12 more hours. This will foster the northeastward ejection of two weak perturbations, now apparent in moisture-channel imagery over the western NE Panhandle/southeastern WY region into southwestern SD, the other over central/eastern CO. By 00Z, these features should reach eastern ND and eastern/southern SD, respectively. At the surface, 11Z analysis showed a low near FSD, with cold front arching southwestward across the NE Sandhills then northwestward to another low over east-central WY near CPR. A quasistationary frontal zone was drawn from the low northeastward over western/ northern MN. The low should move slowly eastward today while the poleward frontal extension moves little, and the cold front moves southeastward into northwestern IA and eastern/central NE. The western segment of that front should hang up over northwestern NE and east-central WY amid mass response to the approaching shortwave trough, which also should induce a surface trough and perhaps secondary/reinforcing baroclinic zone across the lee of the north-central Rockies over eastern WY and into southeastern MT. ...North-central Plains to Upper Midwest... Two main rounds of severe-thunderstorm potential are apparent today, each crossing portions of the main risk area, which represents an aggregated severe potential from both complexes. From east to west: 1. Strong-severe thunderstorms should develop over eastern SD near or north/northwest of the surface low this afternoon -- perhaps arising as early and far west as central SD during midday. This activity will be related to maximized low-level lift associated with the low, and a plume of large-scale ascent preceding the weaker shortwave troughs, and already supporting convection at this time over western SD. Whether the ongoing convection will be continuous with later activity is uncertain. In either event, this eastern complex should intensify substantially over the southeastern SD/southwestern MN/northwestern IA vicinity as it crosses the low-level baroclinic zone and encounters a strongly unstable, richly moist boundary layer, with upper 60s to mid 70s surface dewpoints. Beneath steep lower-middle-level lapse rates, this should contribute to a corridor of 3500-5000 J/kg MLCAPE near I-90 from the FSD area to near the Mississippi River, decreasing to a still-favorable 2000-4000 J/kg in central MN. Supercells with destructive hail, potentially significant-severe gusts, and a few tornadoes are possible, though so is fairly quick upscale expansion. 2. An area of convection may develop as early as late morning to midday well behind the surface cold front, in higher terrain of northern/central WY, initially with a marginal severe threat. This convection should be supported by at least modest low/middle-level moisture, and strong cooling/destabilization aloft, related to the swath of strong large-scale DCVA/ascent immediately preceding the northern Rockies shortwave trough. This activity may be an outgrowth or extension of nonsevere thunderstorms now over extreme western WY near the Star and Hams Fork Valleys and adjacent ranges. These thunderstorms should organize into an MCS and expand/intensify as activity proceeds into greater moisture, instability and storm-relative/post-frontal low-level flow to the east, on the High Plains and near the Black Hills. Northeasterly to easterly flow behind the front and near the trough, beneath strengthening southwest flow aloft, will support 45-60 kt effective-shear magnitudes. Buoyancy will increase eastward as the convection -- which may already have evolve into an outflow-dominant arc by the time it gets into greater moisture east of the Black Hills -- further intensifies into the northern part of a corridor of 1500-2000 J/kg MLCAPE and still-favorable storm-relative boundary- layer flow. Some of this convection may be supercellular to the extent it can remain at least somewhat discrete, with severe wind and large to very large hail possible. With time, wind will dominate as the main threat. This activity should encounter the outflow from the other complex somewhere over southeastern SD or southern MN tonight. Mesoscale uncertainty over the positioning and strength of the outflow (and thus threat of severe to its poleward side) preclude greater unconditional probabilities at this time. Still, a focused corridor of destructive winds remains a possibility across southern parts of SD/MN, some of it potentially affecting areas struck by the first complex. ...Northeastern CONUS... Widely scattered to scattered thunderstorms should develop over portions of eastern NY and New England, as well as parts of western/central PA and northwestern MD -- each moving southward to southeastward through a favorable airmass for organized convection. Strong to locally severe gusts are possible, along with severe hail. Over the New England part of the outlook, cold air aloft, overlying low-level moisture represented by mid/upper 50s F surface dewpoints, should combine with limited diurnal heating to remove MLCINH, and support peak/preconvective MLCAPE ion the 1000-1500 J/kg range. Though low-level flow will be modest, relatively straight/lengthy hodographs will support some hail potential. Further southwest, greater low-level moisture (dewpoints mostly mid/upper 60s to near 70 F at lower elevations) but weaker mid/upper-level lapse rates will be present, yielding similar CAPE values but with different vertical distribution of buoyancy (more skewed to low levels). Still, enough deep/speed shear will be present to support organized multicells and at least transient/isolated supercells. ..Edwards/Bentley.. 08/26/2024 Read more

000
ABPZ20 KNHC 261118
TWOEP

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
500 AM PDT Mon Aug 26 2024

For the eastern North Pacific...east of 140 degrees west longitude:

Active Systems:
The National Hurricane Center is issuing advisories on Hurricane
Gilma, located well east of the Hawaiian Islands and on Tropical
Storm Hector, located well west-southwest of the southern tip of
the Baja California peninsula.

Tropical cyclone formation is not expected during the next 7 days.

&&
Public Advisories on Tropical Storm Hector are issued under WMO
header WTPZ33 KNHC and under AWIPS header MIATCPEP3.
Forecast/Advisories on Tropical Storm Hector are issued under WMO
header WTPZ23 KNHC and under AWIPS header MIATCMEP3.

$$
Forecaster Hagen/Pasch

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0344 AM CDT Mon Aug 26 2024 Valid 291200Z - 031200Z ...DISCUSSION... An upper low is forecast to move across the Canadian Prairie and north-central U.S. through the first half of the Day 4/Thursday period, before being shunted a bit northeastward into Ontario due to pronounced downstream ridging. Timing differences amongst the medium-range global models with the advance of this feature, similarly result in positional differences with the surface front. Thus, while some severe risk may manifest during the afternoon/evening hours across the Upper Midwest region given a likely-to-be-sufficient kinematic and thermodynamic environment ahead of the front, no risk areas will be highlighted at this time. Similarly on Day 5/Friday, timing differences are evident as upper troughing and the associated surface front shift across the Upper Great Lakes/Midwest region. While some severe risk would again be possible within this general region, too much positional uncertainty exists for areal outlines. Beyond Day 5, a gradual expansion of cyclonic flow aloft is forecast across roughly the eastern half of the country -- though to different degrees in the various models. As this occurs, the more favorably moist low-level airmass will gradually be suppressed southward, south of the faster belt of flow aloft, and thus a general decrease in severe risk is expected across the U.S. overall. This trend should continue through the end of the period, as a pronounced intrusion of Canadian air gradually spreads across the eastern two-thirds of the country through Labor Day and beyond. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0344 AM CDT Mon Aug 26 2024 Valid 291200Z - 031200Z ...DISCUSSION... An upper low is forecast to move across the Canadian Prairie and north-central U.S. through the first half of the Day 4/Thursday period, before being shunted a bit northeastward into Ontario due to pronounced downstream ridging. Timing differences amongst the medium-range global models with the advance of this feature, similarly result in positional differences with the surface front. Thus, while some severe risk may manifest during the afternoon/evening hours across the Upper Midwest region given a likely-to-be-sufficient kinematic and thermodynamic environment ahead of the front, no risk areas will be highlighted at this time. Similarly on Day 5/Friday, timing differences are evident as upper troughing and the associated surface front shift across the Upper Great Lakes/Midwest region. While some severe risk would again be possible within this general region, too much positional uncertainty exists for areal outlines. Beyond Day 5, a gradual expansion of cyclonic flow aloft is forecast across roughly the eastern half of the country -- though to different degrees in the various models. As this occurs, the more favorably moist low-level airmass will gradually be suppressed southward, south of the faster belt of flow aloft, and thus a general decrease in severe risk is expected across the U.S. overall. This trend should continue through the end of the period, as a pronounced intrusion of Canadian air gradually spreads across the eastern two-thirds of the country through Labor Day and beyond. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0344 AM CDT Mon Aug 26 2024 Valid 291200Z - 031200Z ...DISCUSSION... An upper low is forecast to move across the Canadian Prairie and north-central U.S. through the first half of the Day 4/Thursday period, before being shunted a bit northeastward into Ontario due to pronounced downstream ridging. Timing differences amongst the medium-range global models with the advance of this feature, similarly result in positional differences with the surface front. Thus, while some severe risk may manifest during the afternoon/evening hours across the Upper Midwest region given a likely-to-be-sufficient kinematic and thermodynamic environment ahead of the front, no risk areas will be highlighted at this time. Similarly on Day 5/Friday, timing differences are evident as upper troughing and the associated surface front shift across the Upper Great Lakes/Midwest region. While some severe risk would again be possible within this general region, too much positional uncertainty exists for areal outlines. Beyond Day 5, a gradual expansion of cyclonic flow aloft is forecast across roughly the eastern half of the country -- though to different degrees in the various models. As this occurs, the more favorably moist low-level airmass will gradually be suppressed southward, south of the faster belt of flow aloft, and thus a general decrease in severe risk is expected across the U.S. overall. This trend should continue through the end of the period, as a pronounced intrusion of Canadian air gradually spreads across the eastern two-thirds of the country through Labor Day and beyond. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0344 AM CDT Mon Aug 26 2024 Valid 291200Z - 031200Z ...DISCUSSION... An upper low is forecast to move across the Canadian Prairie and north-central U.S. through the first half of the Day 4/Thursday period, before being shunted a bit northeastward into Ontario due to pronounced downstream ridging. Timing differences amongst the medium-range global models with the advance of this feature, similarly result in positional differences with the surface front. Thus, while some severe risk may manifest during the afternoon/evening hours across the Upper Midwest region given a likely-to-be-sufficient kinematic and thermodynamic environment ahead of the front, no risk areas will be highlighted at this time. Similarly on Day 5/Friday, timing differences are evident as upper troughing and the associated surface front shift across the Upper Great Lakes/Midwest region. While some severe risk would again be possible within this general region, too much positional uncertainty exists for areal outlines. Beyond Day 5, a gradual expansion of cyclonic flow aloft is forecast across roughly the eastern half of the country -- though to different degrees in the various models. As this occurs, the more favorably moist low-level airmass will gradually be suppressed southward, south of the faster belt of flow aloft, and thus a general decrease in severe risk is expected across the U.S. overall. This trend should continue through the end of the period, as a pronounced intrusion of Canadian air gradually spreads across the eastern two-thirds of the country through Labor Day and beyond. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0344 AM CDT Mon Aug 26 2024 Valid 291200Z - 031200Z ...DISCUSSION... An upper low is forecast to move across the Canadian Prairie and north-central U.S. through the first half of the Day 4/Thursday period, before being shunted a bit northeastward into Ontario due to pronounced downstream ridging. Timing differences amongst the medium-range global models with the advance of this feature, similarly result in positional differences with the surface front. Thus, while some severe risk may manifest during the afternoon/evening hours across the Upper Midwest region given a likely-to-be-sufficient kinematic and thermodynamic environment ahead of the front, no risk areas will be highlighted at this time. Similarly on Day 5/Friday, timing differences are evident as upper troughing and the associated surface front shift across the Upper Great Lakes/Midwest region. While some severe risk would again be possible within this general region, too much positional uncertainty exists for areal outlines. Beyond Day 5, a gradual expansion of cyclonic flow aloft is forecast across roughly the eastern half of the country -- though to different degrees in the various models. As this occurs, the more favorably moist low-level airmass will gradually be suppressed southward, south of the faster belt of flow aloft, and thus a general decrease in severe risk is expected across the U.S. overall. This trend should continue through the end of the period, as a pronounced intrusion of Canadian air gradually spreads across the eastern two-thirds of the country through Labor Day and beyond. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0344 AM CDT Mon Aug 26 2024 Valid 291200Z - 031200Z ...DISCUSSION... An upper low is forecast to move across the Canadian Prairie and north-central U.S. through the first half of the Day 4/Thursday period, before being shunted a bit northeastward into Ontario due to pronounced downstream ridging. Timing differences amongst the medium-range global models with the advance of this feature, similarly result in positional differences with the surface front. Thus, while some severe risk may manifest during the afternoon/evening hours across the Upper Midwest region given a likely-to-be-sufficient kinematic and thermodynamic environment ahead of the front, no risk areas will be highlighted at this time. Similarly on Day 5/Friday, timing differences are evident as upper troughing and the associated surface front shift across the Upper Great Lakes/Midwest region. While some severe risk would again be possible within this general region, too much positional uncertainty exists for areal outlines. Beyond Day 5, a gradual expansion of cyclonic flow aloft is forecast across roughly the eastern half of the country -- though to different degrees in the various models. As this occurs, the more favorably moist low-level airmass will gradually be suppressed southward, south of the faster belt of flow aloft, and thus a general decrease in severe risk is expected across the U.S. overall. This trend should continue through the end of the period, as a pronounced intrusion of Canadian air gradually spreads across the eastern two-thirds of the country through Labor Day and beyond. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0344 AM CDT Mon Aug 26 2024 Valid 291200Z - 031200Z ...DISCUSSION... An upper low is forecast to move across the Canadian Prairie and north-central U.S. through the first half of the Day 4/Thursday period, before being shunted a bit northeastward into Ontario due to pronounced downstream ridging. Timing differences amongst the medium-range global models with the advance of this feature, similarly result in positional differences with the surface front. Thus, while some severe risk may manifest during the afternoon/evening hours across the Upper Midwest region given a likely-to-be-sufficient kinematic and thermodynamic environment ahead of the front, no risk areas will be highlighted at this time. Similarly on Day 5/Friday, timing differences are evident as upper troughing and the associated surface front shift across the Upper Great Lakes/Midwest region. While some severe risk would again be possible within this general region, too much positional uncertainty exists for areal outlines. Beyond Day 5, a gradual expansion of cyclonic flow aloft is forecast across roughly the eastern half of the country -- though to different degrees in the various models. As this occurs, the more favorably moist low-level airmass will gradually be suppressed southward, south of the faster belt of flow aloft, and thus a general decrease in severe risk is expected across the U.S. overall. This trend should continue through the end of the period, as a pronounced intrusion of Canadian air gradually spreads across the eastern two-thirds of the country through Labor Day and beyond. Read more

5-Day Uncertainty Track last updated Mon, 26 Aug 2024 08:36:36 GMT


Wind Speed Probabilities last updated Mon, 26 Aug 2024 09:34:58 GMT

Issued at 1100 PM HST Sun Aug 25 2024 759 WTPZ43 KNHC 260832 TCDEP3 Tropical Storm Hector Discussion Number 3 NWS National Hurricane Center Miami FL EP082024 1100 PM HST Sun Aug 25 2024 Hector has generally changed little during the past several hours. The storm remains sheared with the low-level center located near the northern edge of the main area of deep convection as seen in microwave images. The latest objective and subjective Dvorak estimates range from 35 to 45 kt, and a recent ASCAT-C pass showed a swath of 35-40 kt winds to the east of the center. Based on all of this information, the initial intensity is again held at 40 kt. The storm is moving westward (280 degrees) at 8 kt, and a continued relatively slow westward to west-northwestward motion should persist for another day or two. Thereafter, a slightly faster westward motion is forecast as a low- to mid-level ridge builds to the north of the system. There is some along-track spread in the guidance, but most of the models show a similar theme. Little change was made to the previous NHC track, and this one lies fairly close to the various consensus models. Hector is currently experiencing some northerly wind shear. The shear should decrease a little during the next couple of days, which could allow Hector to gain some strength. However, the strengthening will likely be tempered due to Hector passing over Gilma's cool wake. As Hector nears the central Pacific basin in a few days, the models show the storm moving into a region of stronger shear and drier air, which should end the opportunity for strengthening and induce weakening. The NHC forecast shows Hector becoming a remnant low by day 5, but most of the global models depict this transition occurring sooner than that. The intensity forecast is nudged downward from the previous one, but still lies at the high end of the latest model guidance. FORECAST POSITIONS AND MAX WINDS INIT 26/0900Z 16.3N 123.9W 40 KT 45 MPH 12H 26/1800Z 16.6N 125.3W 45 KT 50 MPH 24H 27/0600Z 17.0N 127.3W 50 KT 60 MPH 36H 27/1800Z 17.4N 129.2W 50 KT 60 MPH 48H 28/0600Z 17.7N 131.4W 50 KT 60 MPH 60H 28/1800Z 17.8N 133.4W 45 KT 50 MPH 72H 29/0600Z 17.9N 135.9W 40 KT 45 MPH 96H 30/0600Z 17.6N 140.8W 35 KT 40 MPH 120H 31/0600Z 17.0N 146.6W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ Forecaster Cangialosi

5-Day Uncertainty Track last updated Mon, 26 Aug 2024 08:32:38 GMT


Wind Speed Probabilities last updated Mon, 26 Aug 2024 09:29:05 GMT