Severe Storms

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0748 AM CDT Tue Aug 20 2024 Valid 201300Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PREDOMINANTLY OVER PORTIONS OF CENTRAL MONTANA... ...SUMMARY... Severe thunderstorm winds and large hail are possible today, mainly over parts of Montana. ...Synopsis... In mid/upper levels, a rather blocky large-scale pattern will yield very slow evolution of major features through the period. A 500-mb low that has just closed off over southern QC should move southward over central NY through the period, with associated cyclonic flow covering the full extent of the Appalachians and most of the CONUS from the mid/upper Mississippi Valley eastward. An anticyclone will remain anchored over NM, west TX and vicinity, with attached ridging moving slowly eastward over CO and the northern Plains. This will permit strengthening southwest flow aloft to spread out of the northern Rockies and across most of MT through the period, ahead of West Coast troughing. An embedded, weak shortwave trough -- evident in moisture-channel imagery over south-central WA and central OR-- should eject northeastward over the Canadian Rockies, The 11Z surface analysis showed a cold front offshore from New England and the Mid-Atlantic, just offshore from the Carolinas, then across southeastern GA, the eastern FL Panhandle, MS/AL shelf waters, and coastal LA, becoming a warm front northwestward over east and north TX to northeastern NM. The Atlantic segment should proceed farther offshore, and sag southward into portions of northern FL and the north-central Gulf, while the western parts stalls from north-central/northwest TX to northeastern NM. Warm frontogenesis over the north-central High Plains -- just east of a lee trough -- should connect with the south-central High Plains pre-existing frontal zone by late in the period. ...Northern High Plains... Widely scattered to scattered, high-based thunderstorms are expected to form first over higher terrain of southeastern and south-central MT during early/mid afternoon, then move northeastward into a rapidly destabilizing and weakly capped (at most) boundary layer over the adjoining High Plains. Supercells with large hail and isolated severe gusts, as well as small clusters with mainly severe gusts and isolated hail, are possible. Activity should cross much of central MT before becoming weaker and more isolated as it moves into nocturnally stabilizing air this evening. While the WA/OR shortwave trough and associated DCVA/UVV field are progged to pass northwest of the area, it should tighten the height gradient in mid/upper levels. This will combine with low-level southeasterlies to yield favorable deep shear for supercells. Progged effective-shear magnitudes vary highly across models and from place to place within the same model (generally 30-55 kt) depending on depth of the CAPE layer, which mostly is a function of how vigorous and deep the mixing process is. As per its bias, RAP- rooted guidance (RAP, HRRR) appear to be mixing too much over central MT, with most other HREF members and NAM showing more realistic vertical thermodynamic profiles and greater overall buoyancy. Peak MLCAPE should reach 1000-1500 J/kg from northwestern NE to east-central MT, decreasing westward to around 500-1000 J/kg over west-central MT. Higher CAPE values are possible over a narrow, north-south corridor in the western Dakotas, but amidst weaker deep-layer forcing and stronger capping near the mid/upper ridge, inhibiting sustained and especially severe convective potential. ...South-central High Plains... Strong elevation-relative heating will support preferential removal of MLCINH, followed by and related mid/late-afternoon thunderstorm development, over the higher terrain of southern CO, on either side of the San Luis Valley. Activity should move eastward to east- southeastward over deeper, well-mixed boundary layers characteristic of the valley and the High Plains, while offering isolated severe gusts and hail for a few hours before weakening in the evening. This close to the mid/upper anticyclone center, deep-later flow will be weak, keeping shear weak and severe potential isolated and disorganized. However, steep lapse rates in a well-mixed boundary layer may support severe gusts and perhaps hail from the most vigorous, sustained cells and small clusters. ..Edwards/Mosier.. 08/20/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0748 AM CDT Tue Aug 20 2024 Valid 201300Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PREDOMINANTLY OVER PORTIONS OF CENTRAL MONTANA... ...SUMMARY... Severe thunderstorm winds and large hail are possible today, mainly over parts of Montana. ...Synopsis... In mid/upper levels, a rather blocky large-scale pattern will yield very slow evolution of major features through the period. A 500-mb low that has just closed off over southern QC should move southward over central NY through the period, with associated cyclonic flow covering the full extent of the Appalachians and most of the CONUS from the mid/upper Mississippi Valley eastward. An anticyclone will remain anchored over NM, west TX and vicinity, with attached ridging moving slowly eastward over CO and the northern Plains. This will permit strengthening southwest flow aloft to spread out of the northern Rockies and across most of MT through the period, ahead of West Coast troughing. An embedded, weak shortwave trough -- evident in moisture-channel imagery over south-central WA and central OR-- should eject northeastward over the Canadian Rockies, The 11Z surface analysis showed a cold front offshore from New England and the Mid-Atlantic, just offshore from the Carolinas, then across southeastern GA, the eastern FL Panhandle, MS/AL shelf waters, and coastal LA, becoming a warm front northwestward over east and north TX to northeastern NM. The Atlantic segment should proceed farther offshore, and sag southward into portions of northern FL and the north-central Gulf, while the western parts stalls from north-central/northwest TX to northeastern NM. Warm frontogenesis over the north-central High Plains -- just east of a lee trough -- should connect with the south-central High Plains pre-existing frontal zone by late in the period. ...Northern High Plains... Widely scattered to scattered, high-based thunderstorms are expected to form first over higher terrain of southeastern and south-central MT during early/mid afternoon, then move northeastward into a rapidly destabilizing and weakly capped (at most) boundary layer over the adjoining High Plains. Supercells with large hail and isolated severe gusts, as well as small clusters with mainly severe gusts and isolated hail, are possible. Activity should cross much of central MT before becoming weaker and more isolated as it moves into nocturnally stabilizing air this evening. While the WA/OR shortwave trough and associated DCVA/UVV field are progged to pass northwest of the area, it should tighten the height gradient in mid/upper levels. This will combine with low-level southeasterlies to yield favorable deep shear for supercells. Progged effective-shear magnitudes vary highly across models and from place to place within the same model (generally 30-55 kt) depending on depth of the CAPE layer, which mostly is a function of how vigorous and deep the mixing process is. As per its bias, RAP- rooted guidance (RAP, HRRR) appear to be mixing too much over central MT, with most other HREF members and NAM showing more realistic vertical thermodynamic profiles and greater overall buoyancy. Peak MLCAPE should reach 1000-1500 J/kg from northwestern NE to east-central MT, decreasing westward to around 500-1000 J/kg over west-central MT. Higher CAPE values are possible over a narrow, north-south corridor in the western Dakotas, but amidst weaker deep-layer forcing and stronger capping near the mid/upper ridge, inhibiting sustained and especially severe convective potential. ...South-central High Plains... Strong elevation-relative heating will support preferential removal of MLCINH, followed by and related mid/late-afternoon thunderstorm development, over the higher terrain of southern CO, on either side of the San Luis Valley. Activity should move eastward to east- southeastward over deeper, well-mixed boundary layers characteristic of the valley and the High Plains, while offering isolated severe gusts and hail for a few hours before weakening in the evening. This close to the mid/upper anticyclone center, deep-later flow will be weak, keeping shear weak and severe potential isolated and disorganized. However, steep lapse rates in a well-mixed boundary layer may support severe gusts and perhaps hail from the most vigorous, sustained cells and small clusters. ..Edwards/Mosier.. 08/20/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0748 AM CDT Tue Aug 20 2024 Valid 201300Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PREDOMINANTLY OVER PORTIONS OF CENTRAL MONTANA... ...SUMMARY... Severe thunderstorm winds and large hail are possible today, mainly over parts of Montana. ...Synopsis... In mid/upper levels, a rather blocky large-scale pattern will yield very slow evolution of major features through the period. A 500-mb low that has just closed off over southern QC should move southward over central NY through the period, with associated cyclonic flow covering the full extent of the Appalachians and most of the CONUS from the mid/upper Mississippi Valley eastward. An anticyclone will remain anchored over NM, west TX and vicinity, with attached ridging moving slowly eastward over CO and the northern Plains. This will permit strengthening southwest flow aloft to spread out of the northern Rockies and across most of MT through the period, ahead of West Coast troughing. An embedded, weak shortwave trough -- evident in moisture-channel imagery over south-central WA and central OR-- should eject northeastward over the Canadian Rockies, The 11Z surface analysis showed a cold front offshore from New England and the Mid-Atlantic, just offshore from the Carolinas, then across southeastern GA, the eastern FL Panhandle, MS/AL shelf waters, and coastal LA, becoming a warm front northwestward over east and north TX to northeastern NM. The Atlantic segment should proceed farther offshore, and sag southward into portions of northern FL and the north-central Gulf, while the western parts stalls from north-central/northwest TX to northeastern NM. Warm frontogenesis over the north-central High Plains -- just east of a lee trough -- should connect with the south-central High Plains pre-existing frontal zone by late in the period. ...Northern High Plains... Widely scattered to scattered, high-based thunderstorms are expected to form first over higher terrain of southeastern and south-central MT during early/mid afternoon, then move northeastward into a rapidly destabilizing and weakly capped (at most) boundary layer over the adjoining High Plains. Supercells with large hail and isolated severe gusts, as well as small clusters with mainly severe gusts and isolated hail, are possible. Activity should cross much of central MT before becoming weaker and more isolated as it moves into nocturnally stabilizing air this evening. While the WA/OR shortwave trough and associated DCVA/UVV field are progged to pass northwest of the area, it should tighten the height gradient in mid/upper levels. This will combine with low-level southeasterlies to yield favorable deep shear for supercells. Progged effective-shear magnitudes vary highly across models and from place to place within the same model (generally 30-55 kt) depending on depth of the CAPE layer, which mostly is a function of how vigorous and deep the mixing process is. As per its bias, RAP- rooted guidance (RAP, HRRR) appear to be mixing too much over central MT, with most other HREF members and NAM showing more realistic vertical thermodynamic profiles and greater overall buoyancy. Peak MLCAPE should reach 1000-1500 J/kg from northwestern NE to east-central MT, decreasing westward to around 500-1000 J/kg over west-central MT. Higher CAPE values are possible over a narrow, north-south corridor in the western Dakotas, but amidst weaker deep-layer forcing and stronger capping near the mid/upper ridge, inhibiting sustained and especially severe convective potential. ...South-central High Plains... Strong elevation-relative heating will support preferential removal of MLCINH, followed by and related mid/late-afternoon thunderstorm development, over the higher terrain of southern CO, on either side of the San Luis Valley. Activity should move eastward to east- southeastward over deeper, well-mixed boundary layers characteristic of the valley and the High Plains, while offering isolated severe gusts and hail for a few hours before weakening in the evening. This close to the mid/upper anticyclone center, deep-later flow will be weak, keeping shear weak and severe potential isolated and disorganized. However, steep lapse rates in a well-mixed boundary layer may support severe gusts and perhaps hail from the most vigorous, sustained cells and small clusters. ..Edwards/Mosier.. 08/20/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0748 AM CDT Tue Aug 20 2024 Valid 201300Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PREDOMINANTLY OVER PORTIONS OF CENTRAL MONTANA... ...SUMMARY... Severe thunderstorm winds and large hail are possible today, mainly over parts of Montana. ...Synopsis... In mid/upper levels, a rather blocky large-scale pattern will yield very slow evolution of major features through the period. A 500-mb low that has just closed off over southern QC should move southward over central NY through the period, with associated cyclonic flow covering the full extent of the Appalachians and most of the CONUS from the mid/upper Mississippi Valley eastward. An anticyclone will remain anchored over NM, west TX and vicinity, with attached ridging moving slowly eastward over CO and the northern Plains. This will permit strengthening southwest flow aloft to spread out of the northern Rockies and across most of MT through the period, ahead of West Coast troughing. An embedded, weak shortwave trough -- evident in moisture-channel imagery over south-central WA and central OR-- should eject northeastward over the Canadian Rockies, The 11Z surface analysis showed a cold front offshore from New England and the Mid-Atlantic, just offshore from the Carolinas, then across southeastern GA, the eastern FL Panhandle, MS/AL shelf waters, and coastal LA, becoming a warm front northwestward over east and north TX to northeastern NM. The Atlantic segment should proceed farther offshore, and sag southward into portions of northern FL and the north-central Gulf, while the western parts stalls from north-central/northwest TX to northeastern NM. Warm frontogenesis over the north-central High Plains -- just east of a lee trough -- should connect with the south-central High Plains pre-existing frontal zone by late in the period. ...Northern High Plains... Widely scattered to scattered, high-based thunderstorms are expected to form first over higher terrain of southeastern and south-central MT during early/mid afternoon, then move northeastward into a rapidly destabilizing and weakly capped (at most) boundary layer over the adjoining High Plains. Supercells with large hail and isolated severe gusts, as well as small clusters with mainly severe gusts and isolated hail, are possible. Activity should cross much of central MT before becoming weaker and more isolated as it moves into nocturnally stabilizing air this evening. While the WA/OR shortwave trough and associated DCVA/UVV field are progged to pass northwest of the area, it should tighten the height gradient in mid/upper levels. This will combine with low-level southeasterlies to yield favorable deep shear for supercells. Progged effective-shear magnitudes vary highly across models and from place to place within the same model (generally 30-55 kt) depending on depth of the CAPE layer, which mostly is a function of how vigorous and deep the mixing process is. As per its bias, RAP- rooted guidance (RAP, HRRR) appear to be mixing too much over central MT, with most other HREF members and NAM showing more realistic vertical thermodynamic profiles and greater overall buoyancy. Peak MLCAPE should reach 1000-1500 J/kg from northwestern NE to east-central MT, decreasing westward to around 500-1000 J/kg over west-central MT. Higher CAPE values are possible over a narrow, north-south corridor in the western Dakotas, but amidst weaker deep-layer forcing and stronger capping near the mid/upper ridge, inhibiting sustained and especially severe convective potential. ...South-central High Plains... Strong elevation-relative heating will support preferential removal of MLCINH, followed by and related mid/late-afternoon thunderstorm development, over the higher terrain of southern CO, on either side of the San Luis Valley. Activity should move eastward to east- southeastward over deeper, well-mixed boundary layers characteristic of the valley and the High Plains, while offering isolated severe gusts and hail for a few hours before weakening in the evening. This close to the mid/upper anticyclone center, deep-later flow will be weak, keeping shear weak and severe potential isolated and disorganized. However, steep lapse rates in a well-mixed boundary layer may support severe gusts and perhaps hail from the most vigorous, sustained cells and small clusters. ..Edwards/Mosier.. 08/20/2024 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0748 AM CDT Tue Aug 20 2024 Valid 201300Z - 211200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PREDOMINANTLY OVER PORTIONS OF CENTRAL MONTANA... ...SUMMARY... Severe thunderstorm winds and large hail are possible today, mainly over parts of Montana. ...Synopsis... In mid/upper levels, a rather blocky large-scale pattern will yield very slow evolution of major features through the period. A 500-mb low that has just closed off over southern QC should move southward over central NY through the period, with associated cyclonic flow covering the full extent of the Appalachians and most of the CONUS from the mid/upper Mississippi Valley eastward. An anticyclone will remain anchored over NM, west TX and vicinity, with attached ridging moving slowly eastward over CO and the northern Plains. This will permit strengthening southwest flow aloft to spread out of the northern Rockies and across most of MT through the period, ahead of West Coast troughing. An embedded, weak shortwave trough -- evident in moisture-channel imagery over south-central WA and central OR-- should eject northeastward over the Canadian Rockies, The 11Z surface analysis showed a cold front offshore from New England and the Mid-Atlantic, just offshore from the Carolinas, then across southeastern GA, the eastern FL Panhandle, MS/AL shelf waters, and coastal LA, becoming a warm front northwestward over east and north TX to northeastern NM. The Atlantic segment should proceed farther offshore, and sag southward into portions of northern FL and the north-central Gulf, while the western parts stalls from north-central/northwest TX to northeastern NM. Warm frontogenesis over the north-central High Plains -- just east of a lee trough -- should connect with the south-central High Plains pre-existing frontal zone by late in the period. ...Northern High Plains... Widely scattered to scattered, high-based thunderstorms are expected to form first over higher terrain of southeastern and south-central MT during early/mid afternoon, then move northeastward into a rapidly destabilizing and weakly capped (at most) boundary layer over the adjoining High Plains. Supercells with large hail and isolated severe gusts, as well as small clusters with mainly severe gusts and isolated hail, are possible. Activity should cross much of central MT before becoming weaker and more isolated as it moves into nocturnally stabilizing air this evening. While the WA/OR shortwave trough and associated DCVA/UVV field are progged to pass northwest of the area, it should tighten the height gradient in mid/upper levels. This will combine with low-level southeasterlies to yield favorable deep shear for supercells. Progged effective-shear magnitudes vary highly across models and from place to place within the same model (generally 30-55 kt) depending on depth of the CAPE layer, which mostly is a function of how vigorous and deep the mixing process is. As per its bias, RAP- rooted guidance (RAP, HRRR) appear to be mixing too much over central MT, with most other HREF members and NAM showing more realistic vertical thermodynamic profiles and greater overall buoyancy. Peak MLCAPE should reach 1000-1500 J/kg from northwestern NE to east-central MT, decreasing westward to around 500-1000 J/kg over west-central MT. Higher CAPE values are possible over a narrow, north-south corridor in the western Dakotas, but amidst weaker deep-layer forcing and stronger capping near the mid/upper ridge, inhibiting sustained and especially severe convective potential. ...South-central High Plains... Strong elevation-relative heating will support preferential removal of MLCINH, followed by and related mid/late-afternoon thunderstorm development, over the higher terrain of southern CO, on either side of the San Luis Valley. Activity should move eastward to east- southeastward over deeper, well-mixed boundary layers characteristic of the valley and the High Plains, while offering isolated severe gusts and hail for a few hours before weakening in the evening. This close to the mid/upper anticyclone center, deep-later flow will be weak, keeping shear weak and severe potential isolated and disorganized. However, steep lapse rates in a well-mixed boundary layer may support severe gusts and perhaps hail from the most vigorous, sustained cells and small clusters. ..Edwards/Mosier.. 08/20/2024 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0338 AM CDT Tue Aug 20 2024 Valid 231200Z - 281200Z ...DISCUSSION... ...Friday/Day 4 to Sunday/Day 6... Heights within the persistent central U.S. upper-level ridge are forecast to rise from Friday to Sunday, as a mid-level trough moves through the western U.S. An axis of maximized low-level moisture and instability is forecast to remain over the central and northern Plains extending south-southeastward into the mid Missouri Valley. Thunderstorm development, with a potential severe threat, will be possible across parts of this unstable airmass each afternoon and evening. Subsidence associated with the upper-level ridge will be a negative factor, which is expected to keep the severe threat isolated and marginal through the weekend. ...Monday/Day 7 and Tuesday/Day 8... The medium-range models are finally in agreement concerning the timing of an upper-level trough, which is forecast to move through the northern Plains on Monday. Ahead of this trough, a moist and unstable airmass is forecast from the mid Missouri Valley northeastward into the western Great Lakes. Thunderstorms are expected to develop ahead of the trough over parts of the Minnesota and Wisconsin, with more isolated convection southward into Iowa. Strong instability and moderate deep-layer shear should be favorable for a severe threat, with the most likely area in the upper Mississippi Valley Monday afternoon and evening. However, there is still uncertainty concerning the timing of the trough, and location of the instability axis on Monday. In addition, part of the airmass could remain capped. At this point, will not outlook a threat area. The potential severe threat is forecast to shift eastward into the central Great Lakes region on Tuesday, but could be isolated due to the presence of a northeastern U.S. upper-level ridge. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0338 AM CDT Tue Aug 20 2024 Valid 231200Z - 281200Z ...DISCUSSION... ...Friday/Day 4 to Sunday/Day 6... Heights within the persistent central U.S. upper-level ridge are forecast to rise from Friday to Sunday, as a mid-level trough moves through the western U.S. An axis of maximized low-level moisture and instability is forecast to remain over the central and northern Plains extending south-southeastward into the mid Missouri Valley. Thunderstorm development, with a potential severe threat, will be possible across parts of this unstable airmass each afternoon and evening. Subsidence associated with the upper-level ridge will be a negative factor, which is expected to keep the severe threat isolated and marginal through the weekend. ...Monday/Day 7 and Tuesday/Day 8... The medium-range models are finally in agreement concerning the timing of an upper-level trough, which is forecast to move through the northern Plains on Monday. Ahead of this trough, a moist and unstable airmass is forecast from the mid Missouri Valley northeastward into the western Great Lakes. Thunderstorms are expected to develop ahead of the trough over parts of the Minnesota and Wisconsin, with more isolated convection southward into Iowa. Strong instability and moderate deep-layer shear should be favorable for a severe threat, with the most likely area in the upper Mississippi Valley Monday afternoon and evening. However, there is still uncertainty concerning the timing of the trough, and location of the instability axis on Monday. In addition, part of the airmass could remain capped. At this point, will not outlook a threat area. The potential severe threat is forecast to shift eastward into the central Great Lakes region on Tuesday, but could be isolated due to the presence of a northeastern U.S. upper-level ridge. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0338 AM CDT Tue Aug 20 2024 Valid 231200Z - 281200Z ...DISCUSSION... ...Friday/Day 4 to Sunday/Day 6... Heights within the persistent central U.S. upper-level ridge are forecast to rise from Friday to Sunday, as a mid-level trough moves through the western U.S. An axis of maximized low-level moisture and instability is forecast to remain over the central and northern Plains extending south-southeastward into the mid Missouri Valley. Thunderstorm development, with a potential severe threat, will be possible across parts of this unstable airmass each afternoon and evening. Subsidence associated with the upper-level ridge will be a negative factor, which is expected to keep the severe threat isolated and marginal through the weekend. ...Monday/Day 7 and Tuesday/Day 8... The medium-range models are finally in agreement concerning the timing of an upper-level trough, which is forecast to move through the northern Plains on Monday. Ahead of this trough, a moist and unstable airmass is forecast from the mid Missouri Valley northeastward into the western Great Lakes. Thunderstorms are expected to develop ahead of the trough over parts of the Minnesota and Wisconsin, with more isolated convection southward into Iowa. Strong instability and moderate deep-layer shear should be favorable for a severe threat, with the most likely area in the upper Mississippi Valley Monday afternoon and evening. However, there is still uncertainty concerning the timing of the trough, and location of the instability axis on Monday. In addition, part of the airmass could remain capped. At this point, will not outlook a threat area. The potential severe threat is forecast to shift eastward into the central Great Lakes region on Tuesday, but could be isolated due to the presence of a northeastern U.S. upper-level ridge. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0338 AM CDT Tue Aug 20 2024 Valid 231200Z - 281200Z ...DISCUSSION... ...Friday/Day 4 to Sunday/Day 6... Heights within the persistent central U.S. upper-level ridge are forecast to rise from Friday to Sunday, as a mid-level trough moves through the western U.S. An axis of maximized low-level moisture and instability is forecast to remain over the central and northern Plains extending south-southeastward into the mid Missouri Valley. Thunderstorm development, with a potential severe threat, will be possible across parts of this unstable airmass each afternoon and evening. Subsidence associated with the upper-level ridge will be a negative factor, which is expected to keep the severe threat isolated and marginal through the weekend. ...Monday/Day 7 and Tuesday/Day 8... The medium-range models are finally in agreement concerning the timing of an upper-level trough, which is forecast to move through the northern Plains on Monday. Ahead of this trough, a moist and unstable airmass is forecast from the mid Missouri Valley northeastward into the western Great Lakes. Thunderstorms are expected to develop ahead of the trough over parts of the Minnesota and Wisconsin, with more isolated convection southward into Iowa. Strong instability and moderate deep-layer shear should be favorable for a severe threat, with the most likely area in the upper Mississippi Valley Monday afternoon and evening. However, there is still uncertainty concerning the timing of the trough, and location of the instability axis on Monday. In addition, part of the airmass could remain capped. At this point, will not outlook a threat area. The potential severe threat is forecast to shift eastward into the central Great Lakes region on Tuesday, but could be isolated due to the presence of a northeastern U.S. upper-level ridge. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0338 AM CDT Tue Aug 20 2024 Valid 231200Z - 281200Z ...DISCUSSION... ...Friday/Day 4 to Sunday/Day 6... Heights within the persistent central U.S. upper-level ridge are forecast to rise from Friday to Sunday, as a mid-level trough moves through the western U.S. An axis of maximized low-level moisture and instability is forecast to remain over the central and northern Plains extending south-southeastward into the mid Missouri Valley. Thunderstorm development, with a potential severe threat, will be possible across parts of this unstable airmass each afternoon and evening. Subsidence associated with the upper-level ridge will be a negative factor, which is expected to keep the severe threat isolated and marginal through the weekend. ...Monday/Day 7 and Tuesday/Day 8... The medium-range models are finally in agreement concerning the timing of an upper-level trough, which is forecast to move through the northern Plains on Monday. Ahead of this trough, a moist and unstable airmass is forecast from the mid Missouri Valley northeastward into the western Great Lakes. Thunderstorms are expected to develop ahead of the trough over parts of the Minnesota and Wisconsin, with more isolated convection southward into Iowa. Strong instability and moderate deep-layer shear should be favorable for a severe threat, with the most likely area in the upper Mississippi Valley Monday afternoon and evening. However, there is still uncertainty concerning the timing of the trough, and location of the instability axis on Monday. In addition, part of the airmass could remain capped. At this point, will not outlook a threat area. The potential severe threat is forecast to shift eastward into the central Great Lakes region on Tuesday, but could be isolated due to the presence of a northeastern U.S. upper-level ridge. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0338 AM CDT Tue Aug 20 2024 Valid 231200Z - 281200Z ...DISCUSSION... ...Friday/Day 4 to Sunday/Day 6... Heights within the persistent central U.S. upper-level ridge are forecast to rise from Friday to Sunday, as a mid-level trough moves through the western U.S. An axis of maximized low-level moisture and instability is forecast to remain over the central and northern Plains extending south-southeastward into the mid Missouri Valley. Thunderstorm development, with a potential severe threat, will be possible across parts of this unstable airmass each afternoon and evening. Subsidence associated with the upper-level ridge will be a negative factor, which is expected to keep the severe threat isolated and marginal through the weekend. ...Monday/Day 7 and Tuesday/Day 8... The medium-range models are finally in agreement concerning the timing of an upper-level trough, which is forecast to move through the northern Plains on Monday. Ahead of this trough, a moist and unstable airmass is forecast from the mid Missouri Valley northeastward into the western Great Lakes. Thunderstorms are expected to develop ahead of the trough over parts of the Minnesota and Wisconsin, with more isolated convection southward into Iowa. Strong instability and moderate deep-layer shear should be favorable for a severe threat, with the most likely area in the upper Mississippi Valley Monday afternoon and evening. However, there is still uncertainty concerning the timing of the trough, and location of the instability axis on Monday. In addition, part of the airmass could remain capped. At this point, will not outlook a threat area. The potential severe threat is forecast to shift eastward into the central Great Lakes region on Tuesday, but could be isolated due to the presence of a northeastern U.S. upper-level ridge. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0218 AM CDT Tue Aug 20 2024 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS... ...SUMMARY... Thunderstorms with hail and a few marginally severe gusts will be possible on Thursday across parts of the central and northern Plains. ...Central and Northern Plains... An upper-level ridge is forecast to move eastward across the central and northern Plains on Thursday. To the west of the ridge, an axis of instability is forecast to be in place from western Kansas northward into east-central North Dakota. Near this axis, surface dewpoints in the mid to upper 60s F will contribute to the development of moderate instability by afternoon. In addition to the instability, 0-6 km shear is forecast to be in the 25 to 35 knot range along much of this corridor, which should be sufficient for an isolated severe threat. As surface temperatures warm during the day, any cell that can initiate near the instability axis could have potential for hail and severe gusts. There is some uncertainty concerning Thursday's forecast. First, the models vary considerably on the distribution and magnitude of instability. Second, the models differ significantly on convective coverage. The current thinking is that storm coverage will remain relatively isolated due to subsidence in the wake of the ridge, and that convection may tend to develop further to the east away from the instability axis. For this reason, a marginal risk should be sufficient for this forecast. ..Broyles.. 08/20/2024 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0218 AM CDT Tue Aug 20 2024 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS... ...SUMMARY... Thunderstorms with hail and a few marginally severe gusts will be possible on Thursday across parts of the central and northern Plains. ...Central and Northern Plains... An upper-level ridge is forecast to move eastward across the central and northern Plains on Thursday. To the west of the ridge, an axis of instability is forecast to be in place from western Kansas northward into east-central North Dakota. Near this axis, surface dewpoints in the mid to upper 60s F will contribute to the development of moderate instability by afternoon. In addition to the instability, 0-6 km shear is forecast to be in the 25 to 35 knot range along much of this corridor, which should be sufficient for an isolated severe threat. As surface temperatures warm during the day, any cell that can initiate near the instability axis could have potential for hail and severe gusts. There is some uncertainty concerning Thursday's forecast. First, the models vary considerably on the distribution and magnitude of instability. Second, the models differ significantly on convective coverage. The current thinking is that storm coverage will remain relatively isolated due to subsidence in the wake of the ridge, and that convection may tend to develop further to the east away from the instability axis. For this reason, a marginal risk should be sufficient for this forecast. ..Broyles.. 08/20/2024 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0218 AM CDT Tue Aug 20 2024 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS... ...SUMMARY... Thunderstorms with hail and a few marginally severe gusts will be possible on Thursday across parts of the central and northern Plains. ...Central and Northern Plains... An upper-level ridge is forecast to move eastward across the central and northern Plains on Thursday. To the west of the ridge, an axis of instability is forecast to be in place from western Kansas northward into east-central North Dakota. Near this axis, surface dewpoints in the mid to upper 60s F will contribute to the development of moderate instability by afternoon. In addition to the instability, 0-6 km shear is forecast to be in the 25 to 35 knot range along much of this corridor, which should be sufficient for an isolated severe threat. As surface temperatures warm during the day, any cell that can initiate near the instability axis could have potential for hail and severe gusts. There is some uncertainty concerning Thursday's forecast. First, the models vary considerably on the distribution and magnitude of instability. Second, the models differ significantly on convective coverage. The current thinking is that storm coverage will remain relatively isolated due to subsidence in the wake of the ridge, and that convection may tend to develop further to the east away from the instability axis. For this reason, a marginal risk should be sufficient for this forecast. ..Broyles.. 08/20/2024 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0218 AM CDT Tue Aug 20 2024 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS... ...SUMMARY... Thunderstorms with hail and a few marginally severe gusts will be possible on Thursday across parts of the central and northern Plains. ...Central and Northern Plains... An upper-level ridge is forecast to move eastward across the central and northern Plains on Thursday. To the west of the ridge, an axis of instability is forecast to be in place from western Kansas northward into east-central North Dakota. Near this axis, surface dewpoints in the mid to upper 60s F will contribute to the development of moderate instability by afternoon. In addition to the instability, 0-6 km shear is forecast to be in the 25 to 35 knot range along much of this corridor, which should be sufficient for an isolated severe threat. As surface temperatures warm during the day, any cell that can initiate near the instability axis could have potential for hail and severe gusts. There is some uncertainty concerning Thursday's forecast. First, the models vary considerably on the distribution and magnitude of instability. Second, the models differ significantly on convective coverage. The current thinking is that storm coverage will remain relatively isolated due to subsidence in the wake of the ridge, and that convection may tend to develop further to the east away from the instability axis. For this reason, a marginal risk should be sufficient for this forecast. ..Broyles.. 08/20/2024 Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0218 AM CDT Tue Aug 20 2024 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL AND NORTHERN PLAINS... ...SUMMARY... Thunderstorms with hail and a few marginally severe gusts will be possible on Thursday across parts of the central and northern Plains. ...Central and Northern Plains... An upper-level ridge is forecast to move eastward across the central and northern Plains on Thursday. To the west of the ridge, an axis of instability is forecast to be in place from western Kansas northward into east-central North Dakota. Near this axis, surface dewpoints in the mid to upper 60s F will contribute to the development of moderate instability by afternoon. In addition to the instability, 0-6 km shear is forecast to be in the 25 to 35 knot range along much of this corridor, which should be sufficient for an isolated severe threat. As surface temperatures warm during the day, any cell that can initiate near the instability axis could have potential for hail and severe gusts. There is some uncertainty concerning Thursday's forecast. First, the models vary considerably on the distribution and magnitude of instability. Second, the models differ significantly on convective coverage. The current thinking is that storm coverage will remain relatively isolated due to subsidence in the wake of the ridge, and that convection may tend to develop further to the east away from the instability axis. For this reason, a marginal risk should be sufficient for this forecast. ..Broyles.. 08/20/2024 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0143 AM CDT Tue Aug 20 2024 Valid 211200Z - 221200Z ...Synopsis... Broad southwesterly mid-level flow, and a progressive shortwave trough moving through the northern Great Basin/Northwest U.S., will bring sustained dry/windy conditions to portions of Nevada, Utah, and Idaho on Wednesday. ...Dry/Windy... Deep boundary-layer mixing beneath broad southwesterly mid-level flow, and a progressive shortwave trough moving from northern Nevada/southern Oregon into Idaho and Montana, will be responsible for elevated fire-weather conditions across the Great Basin on Wednesday. High-resolution ensemble guidance suggests there may be a narrow corridor of critical fire-weather conditions across Nevada, where relative humidity values will drop into the single digits and winds could get as high as 20-25 MPH. This area currently overlaps with fuels that are not expected to be receptive to wildfire spread, with ERC values around the 60th-65th annual percentiles. However, with dry/windy conditions expected the preceding day, some additional curing of fuels can be expected, and critical highlights could be needed in subsequent updates. ...Dry Thunderstorms... A mix of wet and dry thunderstorms will be possible across southwestern Montana, with additional dry thunderstorm development likely across southern Colorado and northern New Mexico. However, current fuels guidance suggests that both of these regions are unlikely to be receptive to new ignitions and wildfire spread, with ERC values below the 60th annual percentile for both regions. ..Halbert/Squitieri.. 08/20/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0143 AM CDT Tue Aug 20 2024 Valid 211200Z - 221200Z ...Synopsis... Broad southwesterly mid-level flow, and a progressive shortwave trough moving through the northern Great Basin/Northwest U.S., will bring sustained dry/windy conditions to portions of Nevada, Utah, and Idaho on Wednesday. ...Dry/Windy... Deep boundary-layer mixing beneath broad southwesterly mid-level flow, and a progressive shortwave trough moving from northern Nevada/southern Oregon into Idaho and Montana, will be responsible for elevated fire-weather conditions across the Great Basin on Wednesday. High-resolution ensemble guidance suggests there may be a narrow corridor of critical fire-weather conditions across Nevada, where relative humidity values will drop into the single digits and winds could get as high as 20-25 MPH. This area currently overlaps with fuels that are not expected to be receptive to wildfire spread, with ERC values around the 60th-65th annual percentiles. However, with dry/windy conditions expected the preceding day, some additional curing of fuels can be expected, and critical highlights could be needed in subsequent updates. ...Dry Thunderstorms... A mix of wet and dry thunderstorms will be possible across southwestern Montana, with additional dry thunderstorm development likely across southern Colorado and northern New Mexico. However, current fuels guidance suggests that both of these regions are unlikely to be receptive to new ignitions and wildfire spread, with ERC values below the 60th annual percentile for both regions. ..Halbert/Squitieri.. 08/20/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0143 AM CDT Tue Aug 20 2024 Valid 211200Z - 221200Z ...Synopsis... Broad southwesterly mid-level flow, and a progressive shortwave trough moving through the northern Great Basin/Northwest U.S., will bring sustained dry/windy conditions to portions of Nevada, Utah, and Idaho on Wednesday. ...Dry/Windy... Deep boundary-layer mixing beneath broad southwesterly mid-level flow, and a progressive shortwave trough moving from northern Nevada/southern Oregon into Idaho and Montana, will be responsible for elevated fire-weather conditions across the Great Basin on Wednesday. High-resolution ensemble guidance suggests there may be a narrow corridor of critical fire-weather conditions across Nevada, where relative humidity values will drop into the single digits and winds could get as high as 20-25 MPH. This area currently overlaps with fuels that are not expected to be receptive to wildfire spread, with ERC values around the 60th-65th annual percentiles. However, with dry/windy conditions expected the preceding day, some additional curing of fuels can be expected, and critical highlights could be needed in subsequent updates. ...Dry Thunderstorms... A mix of wet and dry thunderstorms will be possible across southwestern Montana, with additional dry thunderstorm development likely across southern Colorado and northern New Mexico. However, current fuels guidance suggests that both of these regions are unlikely to be receptive to new ignitions and wildfire spread, with ERC values below the 60th annual percentile for both regions. ..Halbert/Squitieri.. 08/20/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0143 AM CDT Tue Aug 20 2024 Valid 211200Z - 221200Z ...Synopsis... Broad southwesterly mid-level flow, and a progressive shortwave trough moving through the northern Great Basin/Northwest U.S., will bring sustained dry/windy conditions to portions of Nevada, Utah, and Idaho on Wednesday. ...Dry/Windy... Deep boundary-layer mixing beneath broad southwesterly mid-level flow, and a progressive shortwave trough moving from northern Nevada/southern Oregon into Idaho and Montana, will be responsible for elevated fire-weather conditions across the Great Basin on Wednesday. High-resolution ensemble guidance suggests there may be a narrow corridor of critical fire-weather conditions across Nevada, where relative humidity values will drop into the single digits and winds could get as high as 20-25 MPH. This area currently overlaps with fuels that are not expected to be receptive to wildfire spread, with ERC values around the 60th-65th annual percentiles. However, with dry/windy conditions expected the preceding day, some additional curing of fuels can be expected, and critical highlights could be needed in subsequent updates. ...Dry Thunderstorms... A mix of wet and dry thunderstorms will be possible across southwestern Montana, with additional dry thunderstorm development likely across southern Colorado and northern New Mexico. However, current fuels guidance suggests that both of these regions are unlikely to be receptive to new ignitions and wildfire spread, with ERC values below the 60th annual percentile for both regions. ..Halbert/Squitieri.. 08/20/2024 ...Please see www.spc.noaa.gov/fire for graphic product... Read more