Severe Storms

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1120 AM CDT Wed Aug 21 2024 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF EASTERN MONTANA AND THE WESTERN DAKOTAS.... ...SUMMARY... Severe hail and thunderstorm gusts are most probable today over parts of eastern Montana and the western Dakotas. ...Northern High Plains... Morning water vapor imagery shows a fast-moving shortwave trough over ID/NV tracking northeastward. Lift associated with this system will overspread parts of MT/WY/Dakotas later this afternoon and evening. This will help to initiate scattered thunderstorms over the higher terrain of southern MT and WY, building eastward into the Plains during the evening. Instability in the mountains is quite weak with dewpoints only in the 40s, but with steep low/mid level lapse rates and moderately strong westerly flow aloft posing a risk of gusty winds. Storms will eventually move/develop eastward into a more moist/unstable air mass across eastern MT and western SD/ND where more robust/severe storms are expected, capable of damaging winds and large hail. ...CO/NE/KS... Ample mid-level moisture will result in scattered afternoon thunderstorms over the mountains of central CO and southern WY. This area will be on the fringe of the stronger westerly flow aloft, and with pockets of strong daytime heating helping to steepen low-level lapse rates. This will promote a risk of gusty/damaging winds in the strongest cells. As the activity spreads eastward into the Plains, further intensification is possible with a few cells continuing a risk of gusty winds and hail during the evening. ...Southeast AZ... Afternoon thunderstorms have been occurring daily over southeast AZ, with isolated strong cells capable of gusty winds. Today will be similar as daytime heating dewpoints in the 60s promote storms over the higher terrain that track slowly northwestward during the late afternoon and early evening. ..Hart/Thornton.. 08/21/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1120 AM CDT Wed Aug 21 2024 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF EASTERN MONTANA AND THE WESTERN DAKOTAS.... ...SUMMARY... Severe hail and thunderstorm gusts are most probable today over parts of eastern Montana and the western Dakotas. ...Northern High Plains... Morning water vapor imagery shows a fast-moving shortwave trough over ID/NV tracking northeastward. Lift associated with this system will overspread parts of MT/WY/Dakotas later this afternoon and evening. This will help to initiate scattered thunderstorms over the higher terrain of southern MT and WY, building eastward into the Plains during the evening. Instability in the mountains is quite weak with dewpoints only in the 40s, but with steep low/mid level lapse rates and moderately strong westerly flow aloft posing a risk of gusty winds. Storms will eventually move/develop eastward into a more moist/unstable air mass across eastern MT and western SD/ND where more robust/severe storms are expected, capable of damaging winds and large hail. ...CO/NE/KS... Ample mid-level moisture will result in scattered afternoon thunderstorms over the mountains of central CO and southern WY. This area will be on the fringe of the stronger westerly flow aloft, and with pockets of strong daytime heating helping to steepen low-level lapse rates. This will promote a risk of gusty/damaging winds in the strongest cells. As the activity spreads eastward into the Plains, further intensification is possible with a few cells continuing a risk of gusty winds and hail during the evening. ...Southeast AZ... Afternoon thunderstorms have been occurring daily over southeast AZ, with isolated strong cells capable of gusty winds. Today will be similar as daytime heating dewpoints in the 60s promote storms over the higher terrain that track slowly northwestward during the late afternoon and early evening. ..Hart/Thornton.. 08/21/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1120 AM CDT Wed Aug 21 2024 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF EASTERN MONTANA AND THE WESTERN DAKOTAS.... ...SUMMARY... Severe hail and thunderstorm gusts are most probable today over parts of eastern Montana and the western Dakotas. ...Northern High Plains... Morning water vapor imagery shows a fast-moving shortwave trough over ID/NV tracking northeastward. Lift associated with this system will overspread parts of MT/WY/Dakotas later this afternoon and evening. This will help to initiate scattered thunderstorms over the higher terrain of southern MT and WY, building eastward into the Plains during the evening. Instability in the mountains is quite weak with dewpoints only in the 40s, but with steep low/mid level lapse rates and moderately strong westerly flow aloft posing a risk of gusty winds. Storms will eventually move/develop eastward into a more moist/unstable air mass across eastern MT and western SD/ND where more robust/severe storms are expected, capable of damaging winds and large hail. ...CO/NE/KS... Ample mid-level moisture will result in scattered afternoon thunderstorms over the mountains of central CO and southern WY. This area will be on the fringe of the stronger westerly flow aloft, and with pockets of strong daytime heating helping to steepen low-level lapse rates. This will promote a risk of gusty/damaging winds in the strongest cells. As the activity spreads eastward into the Plains, further intensification is possible with a few cells continuing a risk of gusty winds and hail during the evening. ...Southeast AZ... Afternoon thunderstorms have been occurring daily over southeast AZ, with isolated strong cells capable of gusty winds. Today will be similar as daytime heating dewpoints in the 60s promote storms over the higher terrain that track slowly northwestward during the late afternoon and early evening. ..Hart/Thornton.. 08/21/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1120 AM CDT Wed Aug 21 2024 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF EASTERN MONTANA AND THE WESTERN DAKOTAS.... ...SUMMARY... Severe hail and thunderstorm gusts are most probable today over parts of eastern Montana and the western Dakotas. ...Northern High Plains... Morning water vapor imagery shows a fast-moving shortwave trough over ID/NV tracking northeastward. Lift associated with this system will overspread parts of MT/WY/Dakotas later this afternoon and evening. This will help to initiate scattered thunderstorms over the higher terrain of southern MT and WY, building eastward into the Plains during the evening. Instability in the mountains is quite weak with dewpoints only in the 40s, but with steep low/mid level lapse rates and moderately strong westerly flow aloft posing a risk of gusty winds. Storms will eventually move/develop eastward into a more moist/unstable air mass across eastern MT and western SD/ND where more robust/severe storms are expected, capable of damaging winds and large hail. ...CO/NE/KS... Ample mid-level moisture will result in scattered afternoon thunderstorms over the mountains of central CO and southern WY. This area will be on the fringe of the stronger westerly flow aloft, and with pockets of strong daytime heating helping to steepen low-level lapse rates. This will promote a risk of gusty/damaging winds in the strongest cells. As the activity spreads eastward into the Plains, further intensification is possible with a few cells continuing a risk of gusty winds and hail during the evening. ...Southeast AZ... Afternoon thunderstorms have been occurring daily over southeast AZ, with isolated strong cells capable of gusty winds. Today will be similar as daytime heating dewpoints in the 60s promote storms over the higher terrain that track slowly northwestward during the late afternoon and early evening. ..Hart/Thornton.. 08/21/2024 Read more

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1120 AM CDT Wed Aug 21 2024 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF EASTERN MONTANA AND THE WESTERN DAKOTAS.... ...SUMMARY... Severe hail and thunderstorm gusts are most probable today over parts of eastern Montana and the western Dakotas. ...Northern High Plains... Morning water vapor imagery shows a fast-moving shortwave trough over ID/NV tracking northeastward. Lift associated with this system will overspread parts of MT/WY/Dakotas later this afternoon and evening. This will help to initiate scattered thunderstorms over the higher terrain of southern MT and WY, building eastward into the Plains during the evening. Instability in the mountains is quite weak with dewpoints only in the 40s, but with steep low/mid level lapse rates and moderately strong westerly flow aloft posing a risk of gusty winds. Storms will eventually move/develop eastward into a more moist/unstable air mass across eastern MT and western SD/ND where more robust/severe storms are expected, capable of damaging winds and large hail. ...CO/NE/KS... Ample mid-level moisture will result in scattered afternoon thunderstorms over the mountains of central CO and southern WY. This area will be on the fringe of the stronger westerly flow aloft, and with pockets of strong daytime heating helping to steepen low-level lapse rates. This will promote a risk of gusty/damaging winds in the strongest cells. As the activity spreads eastward into the Plains, further intensification is possible with a few cells continuing a risk of gusty winds and hail during the evening. ...Southeast AZ... Afternoon thunderstorms have been occurring daily over southeast AZ, with isolated strong cells capable of gusty winds. Today will be similar as daytime heating dewpoints in the 60s promote storms over the higher terrain that track slowly northwestward during the late afternoon and early evening. ..Hart/Thornton.. 08/21/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Wed Aug 21 2024 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF EASTERN MONTANA AND WESTERN NORTH DAKOTA... ...SUMMARY... Severe hail and thunderstorm gusts are most probable over parts of eastern Montana and western North Dakota. ...Synopsis... The CONUS portion of the large-scale, mid/upper-level pattern this period will be characterized by mean troughing over the East and West Coasts, and ridging extending northward over the Great Plains States from a high over west TX. A strong cyclone -- initially centered just south of the AK Panhandle -- is expected to dig south-southeastward, with its 500-mb center moving to around 200 nm west of UIL by 12Z tomorrow. As this process reinforces the mean western trough, a series of mostly low-amplitude shortwave perturbations will eject through the foregoing southwest flow. The best-defined and potentially most important of those perturbations evident in moisture-channel imagery over portions of northern CA, northwestern NV and southeastern OR. This feature should reach southeastern ID and west-central MT around 00Z, before ejecting northeastward across the northern High Plains and losing definition tonight. Meanwhile, in the subtropical easterlies, a shortwave trough will continue to drift westward across parts of Sonora, the Gulf of California, and central/northern Baja. At the surface, 11Z analysis showed rich Gulf-origin moisture still confined near and south of a slowly weakening synoptic front over northern FL, the northern Gulf shelf waters, and southeast to north-central TX. Nonetheless, a plume of mainly 60s F surface dewpoints was analyzed from much of OK north-northwestward across western/central portions of KS, NE and the Dakotas. A lee trough was drawn farther west, over eastern portions of MT/WY/CO. This trough should intensify through the day as ridging aloft shifts somewhat eastward, and southwest flow aloft spreads over more of the High Plains. As part of that process, surface cyclogenesis is expected over the northeastern WY/southeastern MT region, with the resulting low shifting eastward into northwestern SD around 06Z. ...Northern Plains... Widely scattered to scattered thunderstorms are expected to develop initially over the higher terrain of south-central/southwestern MT by midafternoon. In this area, heating of greater elevations preferentially removes MLCINH first, as large-scale lift ahead of the ejecting shortwave begins to move overhead. This activity should move northeastward into parts of central MT atop a boundary layer that is diurnally destabilizing/mixing, yet still favorably moist. Additional thunderstorms may develop by late afternoon near the surface trough, where strong surface heating and the western rim of the corridor of greatest moisture (surface dewpoints commonly in the upper 50s to mid 60s F) will remove capping at lower elevations. Convection of both origins may merge near the trough, over eastern MT. Along the way, activity should produce at least occasional large hail (mainly with any sustained supercells) and damaging gusts. Some aggregation of convection should occur, leading to forward-propagational clustering and increased potential for swath(s) of severe to potentially significant (65+ kt) gusts from late afternoon through much of the evening, as activity moves through a lingering, deep, well-mixed layer left by diurnal heating. A well-heated and deep boundary layer west of the moist plume will support MLCAPE in the 500-1500 J/kg range, with 1000-1500 J/kg DCAPE as well. This will foster high-based convection for the first few hours, with some potential for activity to cluster and become collectively outflow-dominant before reaching the grater moisture. weak low-level winds are expected, beneath 50-80 kt flow in the upper half of the buoyant profile, contributing to favorable deep shear (40-50 kt effective) for supercells, and long, relatively straight hodographs supporting splitting storms and hail potential where convection doesn't produce too much outflow too soon. Thunderstorms will move into larger nominal CAPE and greater near- surface moisture over easternmost MT into western ND, where the moist axis should be found, with MLCAPE of 2000-3000 J/kg. Though MLCINH also will be stronger in the higher-CAPE corridor than farther west, forced ascent that is driven by cold-pool processes should sustain some of the strong-severe convection well into ND this evening. Activity should peak near the moist/buoyancy axis and weaken afterword tonight, as it moves into progressively more-stable low-level profile, both with lower ambient theta-e and nocturnal diabatic cooling/stabilization near the surface. ...Central High Plains... Widely scattered to scattered thunderstorms should develop this afternoon over higher terrain from the Black Hills to the Laramie Range and southward over the Front Range, its foothills, and adjoining ridges such as the Cheyenne Ridge and Palmer Divide. This convection should move east toward the lee trough and low-level moist axis, while crossing over a hot, deeply mixed boundary layer. Isolated severe gusts are expected, and severe hail also may be a concern with relatively discrete cells. While vertical shear will be weaker than farther north, strong veering of flow with height (especially near the trough) should contribute enough deep shear (30-40 kt effective mainly north of I-70) for at least brief supercell potential. Aggregation of outflows may foster one or more eastward-surging clusters into this evening from western KS to central SD, and a relatively concentrated local severe-wind threat will exist in any such cluster. However, guidance is too inconsistent in convective evolution and longevity, and in location/number of such clusters, to assign greater unconditional probabilities within the long "marginal" area at this time. ...Southeastern AZ... Scattered thunderstorms are expected to develop this afternoon, at first over higher terrain then across deserts/valleys as outflow/ differential-heating boundaries develop. With a relatively deep layer of south-southeasterly midlevel flow, activity should move generally northwestward. Though most progs keep the flow aloft modest (15 kt or less), some mesoscale enhancement is possible east of the track of a northwestward-moving MCV -- evident in IR satellite imagery over north-central Sonora. The most intense convection will be capable of isolated severe gusts. Clouds related both to earlier/overnight convection over southern AZ, as well as to activity over MX, are south and west of this region already, portending essentially a full day of insolation over the outlook area. Residual lower-elevation surface dewpoints in the 50s to mid 60s should decrease only slightly through the diurnal heating/mixing cycle, offset to some extent by moist advection. MLCAPE in the 1000-2000 J/kg range should develop through early/mid afternoon, atop the well-mixed subcloud/boundary layer. ..Edwards/Mosier.. 08/21/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Wed Aug 21 2024 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF EASTERN MONTANA AND WESTERN NORTH DAKOTA... ...SUMMARY... Severe hail and thunderstorm gusts are most probable over parts of eastern Montana and western North Dakota. ...Synopsis... The CONUS portion of the large-scale, mid/upper-level pattern this period will be characterized by mean troughing over the East and West Coasts, and ridging extending northward over the Great Plains States from a high over west TX. A strong cyclone -- initially centered just south of the AK Panhandle -- is expected to dig south-southeastward, with its 500-mb center moving to around 200 nm west of UIL by 12Z tomorrow. As this process reinforces the mean western trough, a series of mostly low-amplitude shortwave perturbations will eject through the foregoing southwest flow. The best-defined and potentially most important of those perturbations evident in moisture-channel imagery over portions of northern CA, northwestern NV and southeastern OR. This feature should reach southeastern ID and west-central MT around 00Z, before ejecting northeastward across the northern High Plains and losing definition tonight. Meanwhile, in the subtropical easterlies, a shortwave trough will continue to drift westward across parts of Sonora, the Gulf of California, and central/northern Baja. At the surface, 11Z analysis showed rich Gulf-origin moisture still confined near and south of a slowly weakening synoptic front over northern FL, the northern Gulf shelf waters, and southeast to north-central TX. Nonetheless, a plume of mainly 60s F surface dewpoints was analyzed from much of OK north-northwestward across western/central portions of KS, NE and the Dakotas. A lee trough was drawn farther west, over eastern portions of MT/WY/CO. This trough should intensify through the day as ridging aloft shifts somewhat eastward, and southwest flow aloft spreads over more of the High Plains. As part of that process, surface cyclogenesis is expected over the northeastern WY/southeastern MT region, with the resulting low shifting eastward into northwestern SD around 06Z. ...Northern Plains... Widely scattered to scattered thunderstorms are expected to develop initially over the higher terrain of south-central/southwestern MT by midafternoon. In this area, heating of greater elevations preferentially removes MLCINH first, as large-scale lift ahead of the ejecting shortwave begins to move overhead. This activity should move northeastward into parts of central MT atop a boundary layer that is diurnally destabilizing/mixing, yet still favorably moist. Additional thunderstorms may develop by late afternoon near the surface trough, where strong surface heating and the western rim of the corridor of greatest moisture (surface dewpoints commonly in the upper 50s to mid 60s F) will remove capping at lower elevations. Convection of both origins may merge near the trough, over eastern MT. Along the way, activity should produce at least occasional large hail (mainly with any sustained supercells) and damaging gusts. Some aggregation of convection should occur, leading to forward-propagational clustering and increased potential for swath(s) of severe to potentially significant (65+ kt) gusts from late afternoon through much of the evening, as activity moves through a lingering, deep, well-mixed layer left by diurnal heating. A well-heated and deep boundary layer west of the moist plume will support MLCAPE in the 500-1500 J/kg range, with 1000-1500 J/kg DCAPE as well. This will foster high-based convection for the first few hours, with some potential for activity to cluster and become collectively outflow-dominant before reaching the grater moisture. weak low-level winds are expected, beneath 50-80 kt flow in the upper half of the buoyant profile, contributing to favorable deep shear (40-50 kt effective) for supercells, and long, relatively straight hodographs supporting splitting storms and hail potential where convection doesn't produce too much outflow too soon. Thunderstorms will move into larger nominal CAPE and greater near- surface moisture over easternmost MT into western ND, where the moist axis should be found, with MLCAPE of 2000-3000 J/kg. Though MLCINH also will be stronger in the higher-CAPE corridor than farther west, forced ascent that is driven by cold-pool processes should sustain some of the strong-severe convection well into ND this evening. Activity should peak near the moist/buoyancy axis and weaken afterword tonight, as it moves into progressively more-stable low-level profile, both with lower ambient theta-e and nocturnal diabatic cooling/stabilization near the surface. ...Central High Plains... Widely scattered to scattered thunderstorms should develop this afternoon over higher terrain from the Black Hills to the Laramie Range and southward over the Front Range, its foothills, and adjoining ridges such as the Cheyenne Ridge and Palmer Divide. This convection should move east toward the lee trough and low-level moist axis, while crossing over a hot, deeply mixed boundary layer. Isolated severe gusts are expected, and severe hail also may be a concern with relatively discrete cells. While vertical shear will be weaker than farther north, strong veering of flow with height (especially near the trough) should contribute enough deep shear (30-40 kt effective mainly north of I-70) for at least brief supercell potential. Aggregation of outflows may foster one or more eastward-surging clusters into this evening from western KS to central SD, and a relatively concentrated local severe-wind threat will exist in any such cluster. However, guidance is too inconsistent in convective evolution and longevity, and in location/number of such clusters, to assign greater unconditional probabilities within the long "marginal" area at this time. ...Southeastern AZ... Scattered thunderstorms are expected to develop this afternoon, at first over higher terrain then across deserts/valleys as outflow/ differential-heating boundaries develop. With a relatively deep layer of south-southeasterly midlevel flow, activity should move generally northwestward. Though most progs keep the flow aloft modest (15 kt or less), some mesoscale enhancement is possible east of the track of a northwestward-moving MCV -- evident in IR satellite imagery over north-central Sonora. The most intense convection will be capable of isolated severe gusts. Clouds related both to earlier/overnight convection over southern AZ, as well as to activity over MX, are south and west of this region already, portending essentially a full day of insolation over the outlook area. Residual lower-elevation surface dewpoints in the 50s to mid 60s should decrease only slightly through the diurnal heating/mixing cycle, offset to some extent by moist advection. MLCAPE in the 1000-2000 J/kg range should develop through early/mid afternoon, atop the well-mixed subcloud/boundary layer. ..Edwards/Mosier.. 08/21/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Wed Aug 21 2024 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF EASTERN MONTANA AND WESTERN NORTH DAKOTA... ...SUMMARY... Severe hail and thunderstorm gusts are most probable over parts of eastern Montana and western North Dakota. ...Synopsis... The CONUS portion of the large-scale, mid/upper-level pattern this period will be characterized by mean troughing over the East and West Coasts, and ridging extending northward over the Great Plains States from a high over west TX. A strong cyclone -- initially centered just south of the AK Panhandle -- is expected to dig south-southeastward, with its 500-mb center moving to around 200 nm west of UIL by 12Z tomorrow. As this process reinforces the mean western trough, a series of mostly low-amplitude shortwave perturbations will eject through the foregoing southwest flow. The best-defined and potentially most important of those perturbations evident in moisture-channel imagery over portions of northern CA, northwestern NV and southeastern OR. This feature should reach southeastern ID and west-central MT around 00Z, before ejecting northeastward across the northern High Plains and losing definition tonight. Meanwhile, in the subtropical easterlies, a shortwave trough will continue to drift westward across parts of Sonora, the Gulf of California, and central/northern Baja. At the surface, 11Z analysis showed rich Gulf-origin moisture still confined near and south of a slowly weakening synoptic front over northern FL, the northern Gulf shelf waters, and southeast to north-central TX. Nonetheless, a plume of mainly 60s F surface dewpoints was analyzed from much of OK north-northwestward across western/central portions of KS, NE and the Dakotas. A lee trough was drawn farther west, over eastern portions of MT/WY/CO. This trough should intensify through the day as ridging aloft shifts somewhat eastward, and southwest flow aloft spreads over more of the High Plains. As part of that process, surface cyclogenesis is expected over the northeastern WY/southeastern MT region, with the resulting low shifting eastward into northwestern SD around 06Z. ...Northern Plains... Widely scattered to scattered thunderstorms are expected to develop initially over the higher terrain of south-central/southwestern MT by midafternoon. In this area, heating of greater elevations preferentially removes MLCINH first, as large-scale lift ahead of the ejecting shortwave begins to move overhead. This activity should move northeastward into parts of central MT atop a boundary layer that is diurnally destabilizing/mixing, yet still favorably moist. Additional thunderstorms may develop by late afternoon near the surface trough, where strong surface heating and the western rim of the corridor of greatest moisture (surface dewpoints commonly in the upper 50s to mid 60s F) will remove capping at lower elevations. Convection of both origins may merge near the trough, over eastern MT. Along the way, activity should produce at least occasional large hail (mainly with any sustained supercells) and damaging gusts. Some aggregation of convection should occur, leading to forward-propagational clustering and increased potential for swath(s) of severe to potentially significant (65+ kt) gusts from late afternoon through much of the evening, as activity moves through a lingering, deep, well-mixed layer left by diurnal heating. A well-heated and deep boundary layer west of the moist plume will support MLCAPE in the 500-1500 J/kg range, with 1000-1500 J/kg DCAPE as well. This will foster high-based convection for the first few hours, with some potential for activity to cluster and become collectively outflow-dominant before reaching the grater moisture. weak low-level winds are expected, beneath 50-80 kt flow in the upper half of the buoyant profile, contributing to favorable deep shear (40-50 kt effective) for supercells, and long, relatively straight hodographs supporting splitting storms and hail potential where convection doesn't produce too much outflow too soon. Thunderstorms will move into larger nominal CAPE and greater near- surface moisture over easternmost MT into western ND, where the moist axis should be found, with MLCAPE of 2000-3000 J/kg. Though MLCINH also will be stronger in the higher-CAPE corridor than farther west, forced ascent that is driven by cold-pool processes should sustain some of the strong-severe convection well into ND this evening. Activity should peak near the moist/buoyancy axis and weaken afterword tonight, as it moves into progressively more-stable low-level profile, both with lower ambient theta-e and nocturnal diabatic cooling/stabilization near the surface. ...Central High Plains... Widely scattered to scattered thunderstorms should develop this afternoon over higher terrain from the Black Hills to the Laramie Range and southward over the Front Range, its foothills, and adjoining ridges such as the Cheyenne Ridge and Palmer Divide. This convection should move east toward the lee trough and low-level moist axis, while crossing over a hot, deeply mixed boundary layer. Isolated severe gusts are expected, and severe hail also may be a concern with relatively discrete cells. While vertical shear will be weaker than farther north, strong veering of flow with height (especially near the trough) should contribute enough deep shear (30-40 kt effective mainly north of I-70) for at least brief supercell potential. Aggregation of outflows may foster one or more eastward-surging clusters into this evening from western KS to central SD, and a relatively concentrated local severe-wind threat will exist in any such cluster. However, guidance is too inconsistent in convective evolution and longevity, and in location/number of such clusters, to assign greater unconditional probabilities within the long "marginal" area at this time. ...Southeastern AZ... Scattered thunderstorms are expected to develop this afternoon, at first over higher terrain then across deserts/valleys as outflow/ differential-heating boundaries develop. With a relatively deep layer of south-southeasterly midlevel flow, activity should move generally northwestward. Though most progs keep the flow aloft modest (15 kt or less), some mesoscale enhancement is possible east of the track of a northwestward-moving MCV -- evident in IR satellite imagery over north-central Sonora. The most intense convection will be capable of isolated severe gusts. Clouds related both to earlier/overnight convection over southern AZ, as well as to activity over MX, are south and west of this region already, portending essentially a full day of insolation over the outlook area. Residual lower-elevation surface dewpoints in the 50s to mid 60s should decrease only slightly through the diurnal heating/mixing cycle, offset to some extent by moist advection. MLCAPE in the 1000-2000 J/kg range should develop through early/mid afternoon, atop the well-mixed subcloud/boundary layer. ..Edwards/Mosier.. 08/21/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Wed Aug 21 2024 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF EASTERN MONTANA AND WESTERN NORTH DAKOTA... ...SUMMARY... Severe hail and thunderstorm gusts are most probable over parts of eastern Montana and western North Dakota. ...Synopsis... The CONUS portion of the large-scale, mid/upper-level pattern this period will be characterized by mean troughing over the East and West Coasts, and ridging extending northward over the Great Plains States from a high over west TX. A strong cyclone -- initially centered just south of the AK Panhandle -- is expected to dig south-southeastward, with its 500-mb center moving to around 200 nm west of UIL by 12Z tomorrow. As this process reinforces the mean western trough, a series of mostly low-amplitude shortwave perturbations will eject through the foregoing southwest flow. The best-defined and potentially most important of those perturbations evident in moisture-channel imagery over portions of northern CA, northwestern NV and southeastern OR. This feature should reach southeastern ID and west-central MT around 00Z, before ejecting northeastward across the northern High Plains and losing definition tonight. Meanwhile, in the subtropical easterlies, a shortwave trough will continue to drift westward across parts of Sonora, the Gulf of California, and central/northern Baja. At the surface, 11Z analysis showed rich Gulf-origin moisture still confined near and south of a slowly weakening synoptic front over northern FL, the northern Gulf shelf waters, and southeast to north-central TX. Nonetheless, a plume of mainly 60s F surface dewpoints was analyzed from much of OK north-northwestward across western/central portions of KS, NE and the Dakotas. A lee trough was drawn farther west, over eastern portions of MT/WY/CO. This trough should intensify through the day as ridging aloft shifts somewhat eastward, and southwest flow aloft spreads over more of the High Plains. As part of that process, surface cyclogenesis is expected over the northeastern WY/southeastern MT region, with the resulting low shifting eastward into northwestern SD around 06Z. ...Northern Plains... Widely scattered to scattered thunderstorms are expected to develop initially over the higher terrain of south-central/southwestern MT by midafternoon. In this area, heating of greater elevations preferentially removes MLCINH first, as large-scale lift ahead of the ejecting shortwave begins to move overhead. This activity should move northeastward into parts of central MT atop a boundary layer that is diurnally destabilizing/mixing, yet still favorably moist. Additional thunderstorms may develop by late afternoon near the surface trough, where strong surface heating and the western rim of the corridor of greatest moisture (surface dewpoints commonly in the upper 50s to mid 60s F) will remove capping at lower elevations. Convection of both origins may merge near the trough, over eastern MT. Along the way, activity should produce at least occasional large hail (mainly with any sustained supercells) and damaging gusts. Some aggregation of convection should occur, leading to forward-propagational clustering and increased potential for swath(s) of severe to potentially significant (65+ kt) gusts from late afternoon through much of the evening, as activity moves through a lingering, deep, well-mixed layer left by diurnal heating. A well-heated and deep boundary layer west of the moist plume will support MLCAPE in the 500-1500 J/kg range, with 1000-1500 J/kg DCAPE as well. This will foster high-based convection for the first few hours, with some potential for activity to cluster and become collectively outflow-dominant before reaching the grater moisture. weak low-level winds are expected, beneath 50-80 kt flow in the upper half of the buoyant profile, contributing to favorable deep shear (40-50 kt effective) for supercells, and long, relatively straight hodographs supporting splitting storms and hail potential where convection doesn't produce too much outflow too soon. Thunderstorms will move into larger nominal CAPE and greater near- surface moisture over easternmost MT into western ND, where the moist axis should be found, with MLCAPE of 2000-3000 J/kg. Though MLCINH also will be stronger in the higher-CAPE corridor than farther west, forced ascent that is driven by cold-pool processes should sustain some of the strong-severe convection well into ND this evening. Activity should peak near the moist/buoyancy axis and weaken afterword tonight, as it moves into progressively more-stable low-level profile, both with lower ambient theta-e and nocturnal diabatic cooling/stabilization near the surface. ...Central High Plains... Widely scattered to scattered thunderstorms should develop this afternoon over higher terrain from the Black Hills to the Laramie Range and southward over the Front Range, its foothills, and adjoining ridges such as the Cheyenne Ridge and Palmer Divide. This convection should move east toward the lee trough and low-level moist axis, while crossing over a hot, deeply mixed boundary layer. Isolated severe gusts are expected, and severe hail also may be a concern with relatively discrete cells. While vertical shear will be weaker than farther north, strong veering of flow with height (especially near the trough) should contribute enough deep shear (30-40 kt effective mainly north of I-70) for at least brief supercell potential. Aggregation of outflows may foster one or more eastward-surging clusters into this evening from western KS to central SD, and a relatively concentrated local severe-wind threat will exist in any such cluster. However, guidance is too inconsistent in convective evolution and longevity, and in location/number of such clusters, to assign greater unconditional probabilities within the long "marginal" area at this time. ...Southeastern AZ... Scattered thunderstorms are expected to develop this afternoon, at first over higher terrain then across deserts/valleys as outflow/ differential-heating boundaries develop. With a relatively deep layer of south-southeasterly midlevel flow, activity should move generally northwestward. Though most progs keep the flow aloft modest (15 kt or less), some mesoscale enhancement is possible east of the track of a northwestward-moving MCV -- evident in IR satellite imagery over north-central Sonora. The most intense convection will be capable of isolated severe gusts. Clouds related both to earlier/overnight convection over southern AZ, as well as to activity over MX, are south and west of this region already, portending essentially a full day of insolation over the outlook area. Residual lower-elevation surface dewpoints in the 50s to mid 60s should decrease only slightly through the diurnal heating/mixing cycle, offset to some extent by moist advection. MLCAPE in the 1000-2000 J/kg range should develop through early/mid afternoon, atop the well-mixed subcloud/boundary layer. ..Edwards/Mosier.. 08/21/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Wed Aug 21 2024 Valid 211300Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF EASTERN MONTANA AND WESTERN NORTH DAKOTA... ...SUMMARY... Severe hail and thunderstorm gusts are most probable over parts of eastern Montana and western North Dakota. ...Synopsis... The CONUS portion of the large-scale, mid/upper-level pattern this period will be characterized by mean troughing over the East and West Coasts, and ridging extending northward over the Great Plains States from a high over west TX. A strong cyclone -- initially centered just south of the AK Panhandle -- is expected to dig south-southeastward, with its 500-mb center moving to around 200 nm west of UIL by 12Z tomorrow. As this process reinforces the mean western trough, a series of mostly low-amplitude shortwave perturbations will eject through the foregoing southwest flow. The best-defined and potentially most important of those perturbations evident in moisture-channel imagery over portions of northern CA, northwestern NV and southeastern OR. This feature should reach southeastern ID and west-central MT around 00Z, before ejecting northeastward across the northern High Plains and losing definition tonight. Meanwhile, in the subtropical easterlies, a shortwave trough will continue to drift westward across parts of Sonora, the Gulf of California, and central/northern Baja. At the surface, 11Z analysis showed rich Gulf-origin moisture still confined near and south of a slowly weakening synoptic front over northern FL, the northern Gulf shelf waters, and southeast to north-central TX. Nonetheless, a plume of mainly 60s F surface dewpoints was analyzed from much of OK north-northwestward across western/central portions of KS, NE and the Dakotas. A lee trough was drawn farther west, over eastern portions of MT/WY/CO. This trough should intensify through the day as ridging aloft shifts somewhat eastward, and southwest flow aloft spreads over more of the High Plains. As part of that process, surface cyclogenesis is expected over the northeastern WY/southeastern MT region, with the resulting low shifting eastward into northwestern SD around 06Z. ...Northern Plains... Widely scattered to scattered thunderstorms are expected to develop initially over the higher terrain of south-central/southwestern MT by midafternoon. In this area, heating of greater elevations preferentially removes MLCINH first, as large-scale lift ahead of the ejecting shortwave begins to move overhead. This activity should move northeastward into parts of central MT atop a boundary layer that is diurnally destabilizing/mixing, yet still favorably moist. Additional thunderstorms may develop by late afternoon near the surface trough, where strong surface heating and the western rim of the corridor of greatest moisture (surface dewpoints commonly in the upper 50s to mid 60s F) will remove capping at lower elevations. Convection of both origins may merge near the trough, over eastern MT. Along the way, activity should produce at least occasional large hail (mainly with any sustained supercells) and damaging gusts. Some aggregation of convection should occur, leading to forward-propagational clustering and increased potential for swath(s) of severe to potentially significant (65+ kt) gusts from late afternoon through much of the evening, as activity moves through a lingering, deep, well-mixed layer left by diurnal heating. A well-heated and deep boundary layer west of the moist plume will support MLCAPE in the 500-1500 J/kg range, with 1000-1500 J/kg DCAPE as well. This will foster high-based convection for the first few hours, with some potential for activity to cluster and become collectively outflow-dominant before reaching the grater moisture. weak low-level winds are expected, beneath 50-80 kt flow in the upper half of the buoyant profile, contributing to favorable deep shear (40-50 kt effective) for supercells, and long, relatively straight hodographs supporting splitting storms and hail potential where convection doesn't produce too much outflow too soon. Thunderstorms will move into larger nominal CAPE and greater near- surface moisture over easternmost MT into western ND, where the moist axis should be found, with MLCAPE of 2000-3000 J/kg. Though MLCINH also will be stronger in the higher-CAPE corridor than farther west, forced ascent that is driven by cold-pool processes should sustain some of the strong-severe convection well into ND this evening. Activity should peak near the moist/buoyancy axis and weaken afterword tonight, as it moves into progressively more-stable low-level profile, both with lower ambient theta-e and nocturnal diabatic cooling/stabilization near the surface. ...Central High Plains... Widely scattered to scattered thunderstorms should develop this afternoon over higher terrain from the Black Hills to the Laramie Range and southward over the Front Range, its foothills, and adjoining ridges such as the Cheyenne Ridge and Palmer Divide. This convection should move east toward the lee trough and low-level moist axis, while crossing over a hot, deeply mixed boundary layer. Isolated severe gusts are expected, and severe hail also may be a concern with relatively discrete cells. While vertical shear will be weaker than farther north, strong veering of flow with height (especially near the trough) should contribute enough deep shear (30-40 kt effective mainly north of I-70) for at least brief supercell potential. Aggregation of outflows may foster one or more eastward-surging clusters into this evening from western KS to central SD, and a relatively concentrated local severe-wind threat will exist in any such cluster. However, guidance is too inconsistent in convective evolution and longevity, and in location/number of such clusters, to assign greater unconditional probabilities within the long "marginal" area at this time. ...Southeastern AZ... Scattered thunderstorms are expected to develop this afternoon, at first over higher terrain then across deserts/valleys as outflow/ differential-heating boundaries develop. With a relatively deep layer of south-southeasterly midlevel flow, activity should move generally northwestward. Though most progs keep the flow aloft modest (15 kt or less), some mesoscale enhancement is possible east of the track of a northwestward-moving MCV -- evident in IR satellite imagery over north-central Sonora. The most intense convection will be capable of isolated severe gusts. Clouds related both to earlier/overnight convection over southern AZ, as well as to activity over MX, are south and west of this region already, portending essentially a full day of insolation over the outlook area. Residual lower-elevation surface dewpoints in the 50s to mid 60s should decrease only slightly through the diurnal heating/mixing cycle, offset to some extent by moist advection. MLCAPE in the 1000-2000 J/kg range should develop through early/mid afternoon, atop the well-mixed subcloud/boundary layer. ..Edwards/Mosier.. 08/21/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0355 AM CDT Wed Aug 21 2024 Valid 241200Z - 291200Z ...DISCUSSION... ...Saturday/Day 4 to Monday/Day 6... Heights within an upper-level ridge are forecast to rise across the central and northern U.S over the weekend, as an upper-level trough moves across the western U.S. Isolated severe-thunderstorm development will be possible across the Dakotas in the afternoon and evening both Saturday and Sunday. The best chance for severe storms would be on Sunday as large-scale ascent and deep-layer shear both increase across the northern Plains due to the approach of the trough. The severe threat is forecast to shift eastward into the upper Mississippi Valley on Monday, as the upper-level trough and its associated cold front advance eastward from the northern Plains into the upper Mississippi Valley. ...Tuesday/Day 7 and Wednesday/Day 8... On Tuesday and Wednesday, the upper-level trough is forecast to deamplify as it moves through the Great Lakes region. Another upper-level trough is forecast to move through the western U.S on Tuesday and Wednesday. The best chance for severe storm development would be on Wednesday afternoon along an instability axis, most likely in either eastern parts of the northern Plains or in the upper Mississippi Valley. At this range, large model spread concerning the timing of the trough and distribution of instability suggests uncertainty is substantial. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0355 AM CDT Wed Aug 21 2024 Valid 241200Z - 291200Z ...DISCUSSION... ...Saturday/Day 4 to Monday/Day 6... Heights within an upper-level ridge are forecast to rise across the central and northern U.S over the weekend, as an upper-level trough moves across the western U.S. Isolated severe-thunderstorm development will be possible across the Dakotas in the afternoon and evening both Saturday and Sunday. The best chance for severe storms would be on Sunday as large-scale ascent and deep-layer shear both increase across the northern Plains due to the approach of the trough. The severe threat is forecast to shift eastward into the upper Mississippi Valley on Monday, as the upper-level trough and its associated cold front advance eastward from the northern Plains into the upper Mississippi Valley. ...Tuesday/Day 7 and Wednesday/Day 8... On Tuesday and Wednesday, the upper-level trough is forecast to deamplify as it moves through the Great Lakes region. Another upper-level trough is forecast to move through the western U.S on Tuesday and Wednesday. The best chance for severe storm development would be on Wednesday afternoon along an instability axis, most likely in either eastern parts of the northern Plains or in the upper Mississippi Valley. At this range, large model spread concerning the timing of the trough and distribution of instability suggests uncertainty is substantial. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0355 AM CDT Wed Aug 21 2024 Valid 241200Z - 291200Z ...DISCUSSION... ...Saturday/Day 4 to Monday/Day 6... Heights within an upper-level ridge are forecast to rise across the central and northern U.S over the weekend, as an upper-level trough moves across the western U.S. Isolated severe-thunderstorm development will be possible across the Dakotas in the afternoon and evening both Saturday and Sunday. The best chance for severe storms would be on Sunday as large-scale ascent and deep-layer shear both increase across the northern Plains due to the approach of the trough. The severe threat is forecast to shift eastward into the upper Mississippi Valley on Monday, as the upper-level trough and its associated cold front advance eastward from the northern Plains into the upper Mississippi Valley. ...Tuesday/Day 7 and Wednesday/Day 8... On Tuesday and Wednesday, the upper-level trough is forecast to deamplify as it moves through the Great Lakes region. Another upper-level trough is forecast to move through the western U.S on Tuesday and Wednesday. The best chance for severe storm development would be on Wednesday afternoon along an instability axis, most likely in either eastern parts of the northern Plains or in the upper Mississippi Valley. At this range, large model spread concerning the timing of the trough and distribution of instability suggests uncertainty is substantial. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0355 AM CDT Wed Aug 21 2024 Valid 241200Z - 291200Z ...DISCUSSION... ...Saturday/Day 4 to Monday/Day 6... Heights within an upper-level ridge are forecast to rise across the central and northern U.S over the weekend, as an upper-level trough moves across the western U.S. Isolated severe-thunderstorm development will be possible across the Dakotas in the afternoon and evening both Saturday and Sunday. The best chance for severe storms would be on Sunday as large-scale ascent and deep-layer shear both increase across the northern Plains due to the approach of the trough. The severe threat is forecast to shift eastward into the upper Mississippi Valley on Monday, as the upper-level trough and its associated cold front advance eastward from the northern Plains into the upper Mississippi Valley. ...Tuesday/Day 7 and Wednesday/Day 8... On Tuesday and Wednesday, the upper-level trough is forecast to deamplify as it moves through the Great Lakes region. Another upper-level trough is forecast to move through the western U.S on Tuesday and Wednesday. The best chance for severe storm development would be on Wednesday afternoon along an instability axis, most likely in either eastern parts of the northern Plains or in the upper Mississippi Valley. At this range, large model spread concerning the timing of the trough and distribution of instability suggests uncertainty is substantial. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0355 AM CDT Wed Aug 21 2024 Valid 241200Z - 291200Z ...DISCUSSION... ...Saturday/Day 4 to Monday/Day 6... Heights within an upper-level ridge are forecast to rise across the central and northern U.S over the weekend, as an upper-level trough moves across the western U.S. Isolated severe-thunderstorm development will be possible across the Dakotas in the afternoon and evening both Saturday and Sunday. The best chance for severe storms would be on Sunday as large-scale ascent and deep-layer shear both increase across the northern Plains due to the approach of the trough. The severe threat is forecast to shift eastward into the upper Mississippi Valley on Monday, as the upper-level trough and its associated cold front advance eastward from the northern Plains into the upper Mississippi Valley. ...Tuesday/Day 7 and Wednesday/Day 8... On Tuesday and Wednesday, the upper-level trough is forecast to deamplify as it moves through the Great Lakes region. Another upper-level trough is forecast to move through the western U.S on Tuesday and Wednesday. The best chance for severe storm development would be on Wednesday afternoon along an instability axis, most likely in either eastern parts of the northern Plains or in the upper Mississippi Valley. At this range, large model spread concerning the timing of the trough and distribution of instability suggests uncertainty is substantial. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CDT Wed Aug 21 2024 Valid 231200Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS...AND IN PARTS OF THE INTERMOUNTAIN WEST AND CENTRAL ROCKIES... ...SUMMARY... Marginally severe storms with hail and isolated severe gusts will be possible on Friday across parts of the central and northern Plains, and in parts of the Intermountain West and central Rockies. ...Central and Northern Plains... An upper-level ridge will remain over eastern parts of the central and northern Plains on Friday. A north-to-south axis of moisture and instability is forecast across Kansas, Nebraska, South Dakota and eastern Montana, where isolated thunderstorm development will be possible during the afternoon and evening. Forecast soundings near the area of strongest instability late Friday afternoon in northern Kansas and southwest Nebraska suggest MLCAPE will peak in the 2000 to 3000 J/kg range and 0-6 km shear will be from 30 to 40 knots. This, combined with steep low to mid-level lapse rates should support an isolated severe threat. However, large-scale ascent is forecast to be absent across much of the region. For this reason, updrafts may struggle to intensify due to subsidence in the wake of the ridge, keeping any severe threat marginal. ...Eastern Utah/Western Colorado/Far Southwest Wyoming... An upper-level low is forecast to approach the coast of Oregon on Friday as southwest mid-level flow remains over much of the Intermountain West. A shortwave trough is forecast to move through the western U.S., which will likely aid the development of scattered thunderstorms in the afternoon from eastern Utah eastward into the central Rockies. The models suggest that weak instability, moderate deep-layer shear and steep low to mid-level lapse rates will be in place, which would be sufficient for marginal severe threat. Hail and isolated severe gusts will be possible mainly during the mid to late afternoon. ..Broyles.. 08/21/2024 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CDT Wed Aug 21 2024 Valid 231200Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS...AND IN PARTS OF THE INTERMOUNTAIN WEST AND CENTRAL ROCKIES... ...SUMMARY... Marginally severe storms with hail and isolated severe gusts will be possible on Friday across parts of the central and northern Plains, and in parts of the Intermountain West and central Rockies. ...Central and Northern Plains... An upper-level ridge will remain over eastern parts of the central and northern Plains on Friday. A north-to-south axis of moisture and instability is forecast across Kansas, Nebraska, South Dakota and eastern Montana, where isolated thunderstorm development will be possible during the afternoon and evening. Forecast soundings near the area of strongest instability late Friday afternoon in northern Kansas and southwest Nebraska suggest MLCAPE will peak in the 2000 to 3000 J/kg range and 0-6 km shear will be from 30 to 40 knots. This, combined with steep low to mid-level lapse rates should support an isolated severe threat. However, large-scale ascent is forecast to be absent across much of the region. For this reason, updrafts may struggle to intensify due to subsidence in the wake of the ridge, keeping any severe threat marginal. ...Eastern Utah/Western Colorado/Far Southwest Wyoming... An upper-level low is forecast to approach the coast of Oregon on Friday as southwest mid-level flow remains over much of the Intermountain West. A shortwave trough is forecast to move through the western U.S., which will likely aid the development of scattered thunderstorms in the afternoon from eastern Utah eastward into the central Rockies. The models suggest that weak instability, moderate deep-layer shear and steep low to mid-level lapse rates will be in place, which would be sufficient for marginal severe threat. Hail and isolated severe gusts will be possible mainly during the mid to late afternoon. ..Broyles.. 08/21/2024 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CDT Wed Aug 21 2024 Valid 231200Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS...AND IN PARTS OF THE INTERMOUNTAIN WEST AND CENTRAL ROCKIES... ...SUMMARY... Marginally severe storms with hail and isolated severe gusts will be possible on Friday across parts of the central and northern Plains, and in parts of the Intermountain West and central Rockies. ...Central and Northern Plains... An upper-level ridge will remain over eastern parts of the central and northern Plains on Friday. A north-to-south axis of moisture and instability is forecast across Kansas, Nebraska, South Dakota and eastern Montana, where isolated thunderstorm development will be possible during the afternoon and evening. Forecast soundings near the area of strongest instability late Friday afternoon in northern Kansas and southwest Nebraska suggest MLCAPE will peak in the 2000 to 3000 J/kg range and 0-6 km shear will be from 30 to 40 knots. This, combined with steep low to mid-level lapse rates should support an isolated severe threat. However, large-scale ascent is forecast to be absent across much of the region. For this reason, updrafts may struggle to intensify due to subsidence in the wake of the ridge, keeping any severe threat marginal. ...Eastern Utah/Western Colorado/Far Southwest Wyoming... An upper-level low is forecast to approach the coast of Oregon on Friday as southwest mid-level flow remains over much of the Intermountain West. A shortwave trough is forecast to move through the western U.S., which will likely aid the development of scattered thunderstorms in the afternoon from eastern Utah eastward into the central Rockies. The models suggest that weak instability, moderate deep-layer shear and steep low to mid-level lapse rates will be in place, which would be sufficient for marginal severe threat. Hail and isolated severe gusts will be possible mainly during the mid to late afternoon. ..Broyles.. 08/21/2024 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0225 AM CDT Wed Aug 21 2024 Valid 231200Z - 241200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS...AND IN PARTS OF THE INTERMOUNTAIN WEST AND CENTRAL ROCKIES... ...SUMMARY... Marginally severe storms with hail and isolated severe gusts will be possible on Friday across parts of the central and northern Plains, and in parts of the Intermountain West and central Rockies. ...Central and Northern Plains... An upper-level ridge will remain over eastern parts of the central and northern Plains on Friday. A north-to-south axis of moisture and instability is forecast across Kansas, Nebraska, South Dakota and eastern Montana, where isolated thunderstorm development will be possible during the afternoon and evening. Forecast soundings near the area of strongest instability late Friday afternoon in northern Kansas and southwest Nebraska suggest MLCAPE will peak in the 2000 to 3000 J/kg range and 0-6 km shear will be from 30 to 40 knots. This, combined with steep low to mid-level lapse rates should support an isolated severe threat. However, large-scale ascent is forecast to be absent across much of the region. For this reason, updrafts may struggle to intensify due to subsidence in the wake of the ridge, keeping any severe threat marginal. ...Eastern Utah/Western Colorado/Far Southwest Wyoming... An upper-level low is forecast to approach the coast of Oregon on Friday as southwest mid-level flow remains over much of the Intermountain West. A shortwave trough is forecast to move through the western U.S., which will likely aid the development of scattered thunderstorms in the afternoon from eastern Utah eastward into the central Rockies. The models suggest that weak instability, moderate deep-layer shear and steep low to mid-level lapse rates will be in place, which would be sufficient for marginal severe threat. Hail and isolated severe gusts will be possible mainly during the mid to late afternoon. ..Broyles.. 08/21/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0145 AM CDT Wed Aug 21 2024 Valid 221200Z - 231200Z ...CRITICAL FIRE WEATHER AREA FOR SOUTHWEST INTO CENTRAL NEVADA... ...Synopsis... A southward-moving shortwave trough is forecast to approach the Oregon/Washington coasts on Thursday, before moving east on Friday. This will result in an intensified height gradient across the Great Basin and a deepening surface low over Oregon that will bring widespread dry/windy conditions to portions of Oregon, Nevada, and Idaho. ...Dry/Windy... Critical fire-weather conditions are forecast across southwestern and central Nevada, where single-digit relative humidity values and winds of 25-30 MPH will overlap with ERC values exceeding the 80th-98th annual percentiles. Uncertainty exists in the eastward extent of the Critical area due to recent wetting rainfall and a tight gradient in fuel receptiveness to wildfire spread, and some areal expansion may be needed in future updates. Elevated fire-weather conditions are expected on the periphery of the Critical highlight area, as well as portions of northwestern Nevada into southeastern Oregon. Southeastern Oregon and northwestern Nevada will have slightly higher boundary-layer relative humidity values of 10-15%, and slightly slower wind speeds of 20-25 MPH. However, fuels in the region are widely receptive to wildfire spread, and if surface winds trend higher, a subsequent upgrade to Critical may be needed in this area. ..Halbert/Squitieri.. 08/21/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more