Severe Storms

SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1130 AM CDT Thu Aug 21 2025 Valid 211630Z - 221200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF EASTERN SOUTH DAKOTA INTO NORTHWEST MINNESOTA... ...SUMMARY... Scattered severe thunderstorms are possible across portions of the northern Plains and Upper Midwest this afternoon into tonight, with severe wind gusts and large hail the primary concerns. A few strong to severe storms may also occur across parts of southern Arizona. ...Northern Plains into the Upper Midwest... Enhanced mid/upper-level westerly flow will persist today across the northern Plains/Upper Midwest, sandwiched between upper troughing over the Canadian Prairie provinces and a stout mid/upper-level anticyclone centered over the Four Corners/Southwest. Multiple low-amplitude perturbations, some associated with ongoing convection across eastern MT into ND and northern MN, will move eastward today and potentially aid in additional thunderstorm development this afternoon and evening. At the surface, the primary low associated with the upper trough will remain well north in Canada, with a trailing cold front expected to continue moving east-southeastward across the northern Plains and Upper Midwest through the period. There is still considerable uncertainty regarding potential robust convective development and subsequent evolution along/near the cold front later today. This is mainly due to the stronger large-scale ascent aloft forecast to remain in central Canada, and capping concerns with southward extent along the front in the northern Plains due to fairly warm low/mid-level temperatures. Multiple potential scenarios remain plausible, ranging from little to no convection developing this afternoon/evening, as some recent convection-allowing model guidance suggests, to multiple supercells/clusters forming in a narrow zone of favorable instability and shear. Given these considerations, confidence is lower than usual regarding severe potential across the northern Plains/Upper Midwest. Still, a narrow corridor of moderate to strong instability will likely exist late this afternoon and into the evening along/near the front from northwest MN into eastern SD, aided by steep mid-level lapse rates and diurnal heating. Modest low-level flow veering to westerly at mid/upper levels will foster sufficient deep-layer shear (around 30-40 kt) to support organized convection, including the potential for a few supercells and clusters. Scattered large hail and severe/damaging winds may occur with this activity if it develops and can be sustained. So, a Slight Risk has been included with this update to account for this potential. Farther west, a post-frontal regime will exist this afternoon/evening across the northern High Plains of northeast WY and vicinity. Low-level upslope flow against the higher terrain may promote a supercell or two to develop and spread east-southeastward through the late afternoon and evening, with mainly an isolated hail threat. Some potential for clustering is also apparent this evening/overnight across parts of SD along/near the surface front. If this occurs, then a continued threat for strong to locally severe gusts may persist. Have therefore connected the Marginal Risks across SD for this possibility. ...Arizona... Modest mid/upper-level easterly flow will persist today over southern AZ, to the south of an anticyclone aloft centered over the Four Corners. Convection that initially develops over the higher terrain of southeast/east-central AZ may gradually develop westward into lower elevations through the late afternoon and continuing into the evening. Ample daytime heating of a seasonably moist low-level airmass already in place (reference observed 12Z PHX sounding) will act to further steepen low/mid-level lapse rates. At least isolated strong to severe gusts may occur with these thunderstorms given the favorable thermodynamic/lapse rate environment. The Marginal Risk has been expanded some to account for latest short-term guidance trends. ..Gleason/Supinie.. 08/21/2025 Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1032 AM CDT Thu Aug 21 2025 Valid 211700Z - 221200Z Scattered high-based showers with isolated embedded thunderstorms are moving northeast over northern Utah, southeast Idaho, and western Wyoming this morning. Isolated to scattered mixed wet/dry remain likely, with the best chances and coverage over the central mountains in Utah through the Uintas and in northwest to north-central Wyoming. Isolated mixed wet/dry thunderstorms are possible in portions of western Colorado, but even without thunderstorm development, enough buoyancy and instability are present to support deep pyroconvection on active large fires in western Colorado. Isolated high-based showers and thunderstorms may continue overnight in portions of central Utah as well. Locally elevated winds/RH remain likely across southern Idaho into western Wyoming and across portions of the southern Great Basin onto the West Slope. Gusty northerly winds are possible late this afternoon and evening in portions of northwest Colorado, southern Wyoming, and northeast Utah associated with a cold front. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0156 AM CDT Thu Aug 21 2025/ ...Synopsis... A strong ridge of high pressure will remain in place over much of the west today and tonight. Beneath the ridge, hot conditions are expected with near record high temperatures. Additionally, monsoon moisture will move northward along the western edge of the ridge supporting shower and thunderstorm chances across portions of the West. ...Great Basin and northern Rockies... At the nose of the monsoon surge, PWAT values are likely to be between 0.5-0.8" with a dry sub-cloud layer and steep low-level lapse rates over portions of Nevada, into Idaho and Wyoming. Storm development is expected along the higher terrain and near a stalled/weakening cold front by early afternoon. Despite slower storm motions and isolated coverage, little wetting rainfall is expected from any of these storms. This should support isolated dry thunderstorm potential with dry fuels in place. Elsewhere, localized dry and breezy conditions are possible over parts of the Snake River Plain, southern Great Basin and northern Colorado this afternoon. While occasional gusts to 15-20 mph overlapping with low RH cannot be ruled out, the coverage of elevated fire-weather potential should remain low/localized. ...California... In addition to the risk for very isolated thunderstorms, hot, dry and unstable conditions are expected across much of the west and southern CA. Locally breezy winds are possible near a thermal trough with very warm temperatures expected over much of the West. Steep mid-level lapse rates and very weak buoyancy could also support some plume dominated fire growth and pyroconvection near large active fires. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1032 AM CDT Thu Aug 21 2025 Valid 211700Z - 221200Z Scattered high-based showers with isolated embedded thunderstorms are moving northeast over northern Utah, southeast Idaho, and western Wyoming this morning. Isolated to scattered mixed wet/dry remain likely, with the best chances and coverage over the central mountains in Utah through the Uintas and in northwest to north-central Wyoming. Isolated mixed wet/dry thunderstorms are possible in portions of western Colorado, but even without thunderstorm development, enough buoyancy and instability are present to support deep pyroconvection on active large fires in western Colorado. Isolated high-based showers and thunderstorms may continue overnight in portions of central Utah as well. Locally elevated winds/RH remain likely across southern Idaho into western Wyoming and across portions of the southern Great Basin onto the West Slope. Gusty northerly winds are possible late this afternoon and evening in portions of northwest Colorado, southern Wyoming, and northeast Utah associated with a cold front. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0156 AM CDT Thu Aug 21 2025/ ...Synopsis... A strong ridge of high pressure will remain in place over much of the west today and tonight. Beneath the ridge, hot conditions are expected with near record high temperatures. Additionally, monsoon moisture will move northward along the western edge of the ridge supporting shower and thunderstorm chances across portions of the West. ...Great Basin and northern Rockies... At the nose of the monsoon surge, PWAT values are likely to be between 0.5-0.8" with a dry sub-cloud layer and steep low-level lapse rates over portions of Nevada, into Idaho and Wyoming. Storm development is expected along the higher terrain and near a stalled/weakening cold front by early afternoon. Despite slower storm motions and isolated coverage, little wetting rainfall is expected from any of these storms. This should support isolated dry thunderstorm potential with dry fuels in place. Elsewhere, localized dry and breezy conditions are possible over parts of the Snake River Plain, southern Great Basin and northern Colorado this afternoon. While occasional gusts to 15-20 mph overlapping with low RH cannot be ruled out, the coverage of elevated fire-weather potential should remain low/localized. ...California... In addition to the risk for very isolated thunderstorms, hot, dry and unstable conditions are expected across much of the west and southern CA. Locally breezy winds are possible near a thermal trough with very warm temperatures expected over much of the West. Steep mid-level lapse rates and very weak buoyancy could also support some plume dominated fire growth and pyroconvection near large active fires. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1032 AM CDT Thu Aug 21 2025 Valid 211700Z - 221200Z Scattered high-based showers with isolated embedded thunderstorms are moving northeast over northern Utah, southeast Idaho, and western Wyoming this morning. Isolated to scattered mixed wet/dry remain likely, with the best chances and coverage over the central mountains in Utah through the Uintas and in northwest to north-central Wyoming. Isolated mixed wet/dry thunderstorms are possible in portions of western Colorado, but even without thunderstorm development, enough buoyancy and instability are present to support deep pyroconvection on active large fires in western Colorado. Isolated high-based showers and thunderstorms may continue overnight in portions of central Utah as well. Locally elevated winds/RH remain likely across southern Idaho into western Wyoming and across portions of the southern Great Basin onto the West Slope. Gusty northerly winds are possible late this afternoon and evening in portions of northwest Colorado, southern Wyoming, and northeast Utah associated with a cold front. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0156 AM CDT Thu Aug 21 2025/ ...Synopsis... A strong ridge of high pressure will remain in place over much of the west today and tonight. Beneath the ridge, hot conditions are expected with near record high temperatures. Additionally, monsoon moisture will move northward along the western edge of the ridge supporting shower and thunderstorm chances across portions of the West. ...Great Basin and northern Rockies... At the nose of the monsoon surge, PWAT values are likely to be between 0.5-0.8" with a dry sub-cloud layer and steep low-level lapse rates over portions of Nevada, into Idaho and Wyoming. Storm development is expected along the higher terrain and near a stalled/weakening cold front by early afternoon. Despite slower storm motions and isolated coverage, little wetting rainfall is expected from any of these storms. This should support isolated dry thunderstorm potential with dry fuels in place. Elsewhere, localized dry and breezy conditions are possible over parts of the Snake River Plain, southern Great Basin and northern Colorado this afternoon. While occasional gusts to 15-20 mph overlapping with low RH cannot be ruled out, the coverage of elevated fire-weather potential should remain low/localized. ...California... In addition to the risk for very isolated thunderstorms, hot, dry and unstable conditions are expected across much of the west and southern CA. Locally breezy winds are possible near a thermal trough with very warm temperatures expected over much of the West. Steep mid-level lapse rates and very weak buoyancy could also support some plume dominated fire growth and pyroconvection near large active fires. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1032 AM CDT Thu Aug 21 2025 Valid 211700Z - 221200Z Scattered high-based showers with isolated embedded thunderstorms are moving northeast over northern Utah, southeast Idaho, and western Wyoming this morning. Isolated to scattered mixed wet/dry remain likely, with the best chances and coverage over the central mountains in Utah through the Uintas and in northwest to north-central Wyoming. Isolated mixed wet/dry thunderstorms are possible in portions of western Colorado, but even without thunderstorm development, enough buoyancy and instability are present to support deep pyroconvection on active large fires in western Colorado. Isolated high-based showers and thunderstorms may continue overnight in portions of central Utah as well. Locally elevated winds/RH remain likely across southern Idaho into western Wyoming and across portions of the southern Great Basin onto the West Slope. Gusty northerly winds are possible late this afternoon and evening in portions of northwest Colorado, southern Wyoming, and northeast Utah associated with a cold front. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0156 AM CDT Thu Aug 21 2025/ ...Synopsis... A strong ridge of high pressure will remain in place over much of the west today and tonight. Beneath the ridge, hot conditions are expected with near record high temperatures. Additionally, monsoon moisture will move northward along the western edge of the ridge supporting shower and thunderstorm chances across portions of the West. ...Great Basin and northern Rockies... At the nose of the monsoon surge, PWAT values are likely to be between 0.5-0.8" with a dry sub-cloud layer and steep low-level lapse rates over portions of Nevada, into Idaho and Wyoming. Storm development is expected along the higher terrain and near a stalled/weakening cold front by early afternoon. Despite slower storm motions and isolated coverage, little wetting rainfall is expected from any of these storms. This should support isolated dry thunderstorm potential with dry fuels in place. Elsewhere, localized dry and breezy conditions are possible over parts of the Snake River Plain, southern Great Basin and northern Colorado this afternoon. While occasional gusts to 15-20 mph overlapping with low RH cannot be ruled out, the coverage of elevated fire-weather potential should remain low/localized. ...California... In addition to the risk for very isolated thunderstorms, hot, dry and unstable conditions are expected across much of the west and southern CA. Locally breezy winds are possible near a thermal trough with very warm temperatures expected over much of the West. Steep mid-level lapse rates and very weak buoyancy could also support some plume dominated fire growth and pyroconvection near large active fires. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1032 AM CDT Thu Aug 21 2025 Valid 211700Z - 221200Z Scattered high-based showers with isolated embedded thunderstorms are moving northeast over northern Utah, southeast Idaho, and western Wyoming this morning. Isolated to scattered mixed wet/dry remain likely, with the best chances and coverage over the central mountains in Utah through the Uintas and in northwest to north-central Wyoming. Isolated mixed wet/dry thunderstorms are possible in portions of western Colorado, but even without thunderstorm development, enough buoyancy and instability are present to support deep pyroconvection on active large fires in western Colorado. Isolated high-based showers and thunderstorms may continue overnight in portions of central Utah as well. Locally elevated winds/RH remain likely across southern Idaho into western Wyoming and across portions of the southern Great Basin onto the West Slope. Gusty northerly winds are possible late this afternoon and evening in portions of northwest Colorado, southern Wyoming, and northeast Utah associated with a cold front. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0156 AM CDT Thu Aug 21 2025/ ...Synopsis... A strong ridge of high pressure will remain in place over much of the west today and tonight. Beneath the ridge, hot conditions are expected with near record high temperatures. Additionally, monsoon moisture will move northward along the western edge of the ridge supporting shower and thunderstorm chances across portions of the West. ...Great Basin and northern Rockies... At the nose of the monsoon surge, PWAT values are likely to be between 0.5-0.8" with a dry sub-cloud layer and steep low-level lapse rates over portions of Nevada, into Idaho and Wyoming. Storm development is expected along the higher terrain and near a stalled/weakening cold front by early afternoon. Despite slower storm motions and isolated coverage, little wetting rainfall is expected from any of these storms. This should support isolated dry thunderstorm potential with dry fuels in place. Elsewhere, localized dry and breezy conditions are possible over parts of the Snake River Plain, southern Great Basin and northern Colorado this afternoon. While occasional gusts to 15-20 mph overlapping with low RH cannot be ruled out, the coverage of elevated fire-weather potential should remain low/localized. ...California... In addition to the risk for very isolated thunderstorms, hot, dry and unstable conditions are expected across much of the west and southern CA. Locally breezy winds are possible near a thermal trough with very warm temperatures expected over much of the West. Steep mid-level lapse rates and very weak buoyancy could also support some plume dominated fire growth and pyroconvection near large active fires. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1032 AM CDT Thu Aug 21 2025 Valid 211700Z - 221200Z Scattered high-based showers with isolated embedded thunderstorms are moving northeast over northern Utah, southeast Idaho, and western Wyoming this morning. Isolated to scattered mixed wet/dry remain likely, with the best chances and coverage over the central mountains in Utah through the Uintas and in northwest to north-central Wyoming. Isolated mixed wet/dry thunderstorms are possible in portions of western Colorado, but even without thunderstorm development, enough buoyancy and instability are present to support deep pyroconvection on active large fires in western Colorado. Isolated high-based showers and thunderstorms may continue overnight in portions of central Utah as well. Locally elevated winds/RH remain likely across southern Idaho into western Wyoming and across portions of the southern Great Basin onto the West Slope. Gusty northerly winds are possible late this afternoon and evening in portions of northwest Colorado, southern Wyoming, and northeast Utah associated with a cold front. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0156 AM CDT Thu Aug 21 2025/ ...Synopsis... A strong ridge of high pressure will remain in place over much of the west today and tonight. Beneath the ridge, hot conditions are expected with near record high temperatures. Additionally, monsoon moisture will move northward along the western edge of the ridge supporting shower and thunderstorm chances across portions of the West. ...Great Basin and northern Rockies... At the nose of the monsoon surge, PWAT values are likely to be between 0.5-0.8" with a dry sub-cloud layer and steep low-level lapse rates over portions of Nevada, into Idaho and Wyoming. Storm development is expected along the higher terrain and near a stalled/weakening cold front by early afternoon. Despite slower storm motions and isolated coverage, little wetting rainfall is expected from any of these storms. This should support isolated dry thunderstorm potential with dry fuels in place. Elsewhere, localized dry and breezy conditions are possible over parts of the Snake River Plain, southern Great Basin and northern Colorado this afternoon. While occasional gusts to 15-20 mph overlapping with low RH cannot be ruled out, the coverage of elevated fire-weather potential should remain low/localized. ...California... In addition to the risk for very isolated thunderstorms, hot, dry and unstable conditions are expected across much of the west and southern CA. Locally breezy winds are possible near a thermal trough with very warm temperatures expected over much of the West. Steep mid-level lapse rates and very weak buoyancy could also support some plume dominated fire growth and pyroconvection near large active fires. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1032 AM CDT Thu Aug 21 2025 Valid 211700Z - 221200Z Scattered high-based showers with isolated embedded thunderstorms are moving northeast over northern Utah, southeast Idaho, and western Wyoming this morning. Isolated to scattered mixed wet/dry remain likely, with the best chances and coverage over the central mountains in Utah through the Uintas and in northwest to north-central Wyoming. Isolated mixed wet/dry thunderstorms are possible in portions of western Colorado, but even without thunderstorm development, enough buoyancy and instability are present to support deep pyroconvection on active large fires in western Colorado. Isolated high-based showers and thunderstorms may continue overnight in portions of central Utah as well. Locally elevated winds/RH remain likely across southern Idaho into western Wyoming and across portions of the southern Great Basin onto the West Slope. Gusty northerly winds are possible late this afternoon and evening in portions of northwest Colorado, southern Wyoming, and northeast Utah associated with a cold front. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0156 AM CDT Thu Aug 21 2025/ ...Synopsis... A strong ridge of high pressure will remain in place over much of the west today and tonight. Beneath the ridge, hot conditions are expected with near record high temperatures. Additionally, monsoon moisture will move northward along the western edge of the ridge supporting shower and thunderstorm chances across portions of the West. ...Great Basin and northern Rockies... At the nose of the monsoon surge, PWAT values are likely to be between 0.5-0.8" with a dry sub-cloud layer and steep low-level lapse rates over portions of Nevada, into Idaho and Wyoming. Storm development is expected along the higher terrain and near a stalled/weakening cold front by early afternoon. Despite slower storm motions and isolated coverage, little wetting rainfall is expected from any of these storms. This should support isolated dry thunderstorm potential with dry fuels in place. Elsewhere, localized dry and breezy conditions are possible over parts of the Snake River Plain, southern Great Basin and northern Colorado this afternoon. While occasional gusts to 15-20 mph overlapping with low RH cannot be ruled out, the coverage of elevated fire-weather potential should remain low/localized. ...California... In addition to the risk for very isolated thunderstorms, hot, dry and unstable conditions are expected across much of the west and southern CA. Locally breezy winds are possible near a thermal trough with very warm temperatures expected over much of the West. Steep mid-level lapse rates and very weak buoyancy could also support some plume dominated fire growth and pyroconvection near large active fires. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Thu Aug 21 2025 Valid 211300Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN PLAINS/UPPER MIDWEST AND SOUTHERN ARIZONA... ...SUMMARY... Isolated severe thunderstorms are possible across portions of the northern Plains and Upper Midwest this afternoon and evening, with severe wind gusts and hail the primary concerns. A few strong to severe storms could also occur across southern Arizona. ...Northern Plains/Minnesota... Late-day height falls are expected regionally in relation to an amplifying shortwave trough over the Canadian prairies. While the primary large-scale forcing will be north of the international border, high-level diffluent flow is expected across the eastern Dakotas/Minnesota, coincident with the front that will be draped across the region at peak heating. Short-term models (HRRR/RRFS) are tending to limit late-afternoon/evening convective development, while most global models and most HREF constituents are a bit more aggressive, which is plausible and lends credence to the potential for at isolated severe storms within a moderately to strongly unstable environment near the front. Deep-layer should be sufficient to potentially yield a few supercells. Increasing storm coverage later into the evening/overnight will be supported by an increasing low-level jet. ...North-central High Plains including eastern Wyoming... Northeasterly low-level upslope flow evolving within the post-frontal environment, and differential heating in vicinity of higher terrain, are expected to influence widely scattered thunderstorm development by late afternoon, particularly across eastern Wyoming. While forecast buoyancy is not expected to be particularly strong, adequate deep-layer shear will prove supportive of organized updrafts that could generate hail/wind, including the possibility that a couple of eastward-moving clusters could evolve by early evening. ...Southern Arizona... The upper ridge should shift slightly northward regionally, with a modest enhancement to mid-level easterly flow late today particularly across southeast Arizona. With isolated storm development expected initially over the rim/mountains this afternoon, storms should drift west-southwestward into a moist/very hot boundary layer, with the potential for outflows/blowing dust to reach the desert floor. ..Guyer/Marsh.. 08/21/2025 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Thu Aug 21 2025 Valid 211300Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN PLAINS/UPPER MIDWEST AND SOUTHERN ARIZONA... ...SUMMARY... Isolated severe thunderstorms are possible across portions of the northern Plains and Upper Midwest this afternoon and evening, with severe wind gusts and hail the primary concerns. A few strong to severe storms could also occur across southern Arizona. ...Northern Plains/Minnesota... Late-day height falls are expected regionally in relation to an amplifying shortwave trough over the Canadian prairies. While the primary large-scale forcing will be north of the international border, high-level diffluent flow is expected across the eastern Dakotas/Minnesota, coincident with the front that will be draped across the region at peak heating. Short-term models (HRRR/RRFS) are tending to limit late-afternoon/evening convective development, while most global models and most HREF constituents are a bit more aggressive, which is plausible and lends credence to the potential for at isolated severe storms within a moderately to strongly unstable environment near the front. Deep-layer should be sufficient to potentially yield a few supercells. Increasing storm coverage later into the evening/overnight will be supported by an increasing low-level jet. ...North-central High Plains including eastern Wyoming... Northeasterly low-level upslope flow evolving within the post-frontal environment, and differential heating in vicinity of higher terrain, are expected to influence widely scattered thunderstorm development by late afternoon, particularly across eastern Wyoming. While forecast buoyancy is not expected to be particularly strong, adequate deep-layer shear will prove supportive of organized updrafts that could generate hail/wind, including the possibility that a couple of eastward-moving clusters could evolve by early evening. ...Southern Arizona... The upper ridge should shift slightly northward regionally, with a modest enhancement to mid-level easterly flow late today particularly across southeast Arizona. With isolated storm development expected initially over the rim/mountains this afternoon, storms should drift west-southwestward into a moist/very hot boundary layer, with the potential for outflows/blowing dust to reach the desert floor. ..Guyer/Marsh.. 08/21/2025 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Thu Aug 21 2025 Valid 211300Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN PLAINS/UPPER MIDWEST AND SOUTHERN ARIZONA... ...SUMMARY... Isolated severe thunderstorms are possible across portions of the northern Plains and Upper Midwest this afternoon and evening, with severe wind gusts and hail the primary concerns. A few strong to severe storms could also occur across southern Arizona. ...Northern Plains/Minnesota... Late-day height falls are expected regionally in relation to an amplifying shortwave trough over the Canadian prairies. While the primary large-scale forcing will be north of the international border, high-level diffluent flow is expected across the eastern Dakotas/Minnesota, coincident with the front that will be draped across the region at peak heating. Short-term models (HRRR/RRFS) are tending to limit late-afternoon/evening convective development, while most global models and most HREF constituents are a bit more aggressive, which is plausible and lends credence to the potential for at isolated severe storms within a moderately to strongly unstable environment near the front. Deep-layer should be sufficient to potentially yield a few supercells. Increasing storm coverage later into the evening/overnight will be supported by an increasing low-level jet. ...North-central High Plains including eastern Wyoming... Northeasterly low-level upslope flow evolving within the post-frontal environment, and differential heating in vicinity of higher terrain, are expected to influence widely scattered thunderstorm development by late afternoon, particularly across eastern Wyoming. While forecast buoyancy is not expected to be particularly strong, adequate deep-layer shear will prove supportive of organized updrafts that could generate hail/wind, including the possibility that a couple of eastward-moving clusters could evolve by early evening. ...Southern Arizona... The upper ridge should shift slightly northward regionally, with a modest enhancement to mid-level easterly flow late today particularly across southeast Arizona. With isolated storm development expected initially over the rim/mountains this afternoon, storms should drift west-southwestward into a moist/very hot boundary layer, with the potential for outflows/blowing dust to reach the desert floor. ..Guyer/Marsh.. 08/21/2025 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Thu Aug 21 2025 Valid 211300Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN PLAINS/UPPER MIDWEST AND SOUTHERN ARIZONA... ...SUMMARY... Isolated severe thunderstorms are possible across portions of the northern Plains and Upper Midwest this afternoon and evening, with severe wind gusts and hail the primary concerns. A few strong to severe storms could also occur across southern Arizona. ...Northern Plains/Minnesota... Late-day height falls are expected regionally in relation to an amplifying shortwave trough over the Canadian prairies. While the primary large-scale forcing will be north of the international border, high-level diffluent flow is expected across the eastern Dakotas/Minnesota, coincident with the front that will be draped across the region at peak heating. Short-term models (HRRR/RRFS) are tending to limit late-afternoon/evening convective development, while most global models and most HREF constituents are a bit more aggressive, which is plausible and lends credence to the potential for at isolated severe storms within a moderately to strongly unstable environment near the front. Deep-layer should be sufficient to potentially yield a few supercells. Increasing storm coverage later into the evening/overnight will be supported by an increasing low-level jet. ...North-central High Plains including eastern Wyoming... Northeasterly low-level upslope flow evolving within the post-frontal environment, and differential heating in vicinity of higher terrain, are expected to influence widely scattered thunderstorm development by late afternoon, particularly across eastern Wyoming. While forecast buoyancy is not expected to be particularly strong, adequate deep-layer shear will prove supportive of organized updrafts that could generate hail/wind, including the possibility that a couple of eastward-moving clusters could evolve by early evening. ...Southern Arizona... The upper ridge should shift slightly northward regionally, with a modest enhancement to mid-level easterly flow late today particularly across southeast Arizona. With isolated storm development expected initially over the rim/mountains this afternoon, storms should drift west-southwestward into a moist/very hot boundary layer, with the potential for outflows/blowing dust to reach the desert floor. ..Guyer/Marsh.. 08/21/2025 Read more

SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0751 AM CDT Thu Aug 21 2025 Valid 211300Z - 221200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE NORTHERN PLAINS/UPPER MIDWEST AND SOUTHERN ARIZONA... ...SUMMARY... Isolated severe thunderstorms are possible across portions of the northern Plains and Upper Midwest this afternoon and evening, with severe wind gusts and hail the primary concerns. A few strong to severe storms could also occur across southern Arizona. ...Northern Plains/Minnesota... Late-day height falls are expected regionally in relation to an amplifying shortwave trough over the Canadian prairies. While the primary large-scale forcing will be north of the international border, high-level diffluent flow is expected across the eastern Dakotas/Minnesota, coincident with the front that will be draped across the region at peak heating. Short-term models (HRRR/RRFS) are tending to limit late-afternoon/evening convective development, while most global models and most HREF constituents are a bit more aggressive, which is plausible and lends credence to the potential for at isolated severe storms within a moderately to strongly unstable environment near the front. Deep-layer should be sufficient to potentially yield a few supercells. Increasing storm coverage later into the evening/overnight will be supported by an increasing low-level jet. ...North-central High Plains including eastern Wyoming... Northeasterly low-level upslope flow evolving within the post-frontal environment, and differential heating in vicinity of higher terrain, are expected to influence widely scattered thunderstorm development by late afternoon, particularly across eastern Wyoming. While forecast buoyancy is not expected to be particularly strong, adequate deep-layer shear will prove supportive of organized updrafts that could generate hail/wind, including the possibility that a couple of eastward-moving clusters could evolve by early evening. ...Southern Arizona... The upper ridge should shift slightly northward regionally, with a modest enhancement to mid-level easterly flow late today particularly across southeast Arizona. With isolated storm development expected initially over the rim/mountains this afternoon, storms should drift west-southwestward into a moist/very hot boundary layer, with the potential for outflows/blowing dust to reach the desert floor. ..Guyer/Marsh.. 08/21/2025 Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0309 AM CDT Thu Aug 21 2025 Valid 241200Z - 291200Z ...DISCUSSION... ...D4/Sunday - D5/Monday... A cold front that moves into the eastern CONUS on Sunday may tend to slow down, as a reinforcing shortwave moves through the base of a deep mid/upper-level trough covering the region. Scattered storms will be possible from the Northeast into the central/southern Appalachians on D4/Sunday, though with only modest instability and deep-layer shear forecast to be in place, any severe potential may remain isolated. Stronger deep-layer flow/shear is generally forecast to overspread parts of the Northeast/New England on D5/Monday, though with generally weak instability expected, severe potential is uncertain. Scattered storms will also be possible on Sunday and Monday across the CO Front Range vicinity into the central High Plains, within a persistent post-frontal regime. While details are uncertain, strong to isolated severe storms cannot be ruled out, especially if any organized clustering can develop and emerge into parts of the High Plains. ...D6/Tuesday - D8/Thursday... While typical model spread is noted by Days 6-8, guidance generally depicts relatively limited severe potential into the middle of next week, as an expansive surface ridge suppresses richer low-level moisture to parts of the Gulf Coast and Texas. Some guidance shows potential for recovery by D8/Thursday across parts of the southern/central Plains, but deep-layer flow is generally forecast to remain weak to modest across the region. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0309 AM CDT Thu Aug 21 2025 Valid 241200Z - 291200Z ...DISCUSSION... ...D4/Sunday - D5/Monday... A cold front that moves into the eastern CONUS on Sunday may tend to slow down, as a reinforcing shortwave moves through the base of a deep mid/upper-level trough covering the region. Scattered storms will be possible from the Northeast into the central/southern Appalachians on D4/Sunday, though with only modest instability and deep-layer shear forecast to be in place, any severe potential may remain isolated. Stronger deep-layer flow/shear is generally forecast to overspread parts of the Northeast/New England on D5/Monday, though with generally weak instability expected, severe potential is uncertain. Scattered storms will also be possible on Sunday and Monday across the CO Front Range vicinity into the central High Plains, within a persistent post-frontal regime. While details are uncertain, strong to isolated severe storms cannot be ruled out, especially if any organized clustering can develop and emerge into parts of the High Plains. ...D6/Tuesday - D8/Thursday... While typical model spread is noted by Days 6-8, guidance generally depicts relatively limited severe potential into the middle of next week, as an expansive surface ridge suppresses richer low-level moisture to parts of the Gulf Coast and Texas. Some guidance shows potential for recovery by D8/Thursday across parts of the southern/central Plains, but deep-layer flow is generally forecast to remain weak to modest across the region. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0309 AM CDT Thu Aug 21 2025 Valid 241200Z - 291200Z ...DISCUSSION... ...D4/Sunday - D5/Monday... A cold front that moves into the eastern CONUS on Sunday may tend to slow down, as a reinforcing shortwave moves through the base of a deep mid/upper-level trough covering the region. Scattered storms will be possible from the Northeast into the central/southern Appalachians on D4/Sunday, though with only modest instability and deep-layer shear forecast to be in place, any severe potential may remain isolated. Stronger deep-layer flow/shear is generally forecast to overspread parts of the Northeast/New England on D5/Monday, though with generally weak instability expected, severe potential is uncertain. Scattered storms will also be possible on Sunday and Monday across the CO Front Range vicinity into the central High Plains, within a persistent post-frontal regime. While details are uncertain, strong to isolated severe storms cannot be ruled out, especially if any organized clustering can develop and emerge into parts of the High Plains. ...D6/Tuesday - D8/Thursday... While typical model spread is noted by Days 6-8, guidance generally depicts relatively limited severe potential into the middle of next week, as an expansive surface ridge suppresses richer low-level moisture to parts of the Gulf Coast and Texas. Some guidance shows potential for recovery by D8/Thursday across parts of the southern/central Plains, but deep-layer flow is generally forecast to remain weak to modest across the region. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0309 AM CDT Thu Aug 21 2025 Valid 241200Z - 291200Z ...DISCUSSION... ...D4/Sunday - D5/Monday... A cold front that moves into the eastern CONUS on Sunday may tend to slow down, as a reinforcing shortwave moves through the base of a deep mid/upper-level trough covering the region. Scattered storms will be possible from the Northeast into the central/southern Appalachians on D4/Sunday, though with only modest instability and deep-layer shear forecast to be in place, any severe potential may remain isolated. Stronger deep-layer flow/shear is generally forecast to overspread parts of the Northeast/New England on D5/Monday, though with generally weak instability expected, severe potential is uncertain. Scattered storms will also be possible on Sunday and Monday across the CO Front Range vicinity into the central High Plains, within a persistent post-frontal regime. While details are uncertain, strong to isolated severe storms cannot be ruled out, especially if any organized clustering can develop and emerge into parts of the High Plains. ...D6/Tuesday - D8/Thursday... While typical model spread is noted by Days 6-8, guidance generally depicts relatively limited severe potential into the middle of next week, as an expansive surface ridge suppresses richer low-level moisture to parts of the Gulf Coast and Texas. Some guidance shows potential for recovery by D8/Thursday across parts of the southern/central Plains, but deep-layer flow is generally forecast to remain weak to modest across the region. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0309 AM CDT Thu Aug 21 2025 Valid 241200Z - 291200Z ...DISCUSSION... ...D4/Sunday - D5/Monday... A cold front that moves into the eastern CONUS on Sunday may tend to slow down, as a reinforcing shortwave moves through the base of a deep mid/upper-level trough covering the region. Scattered storms will be possible from the Northeast into the central/southern Appalachians on D4/Sunday, though with only modest instability and deep-layer shear forecast to be in place, any severe potential may remain isolated. Stronger deep-layer flow/shear is generally forecast to overspread parts of the Northeast/New England on D5/Monday, though with generally weak instability expected, severe potential is uncertain. Scattered storms will also be possible on Sunday and Monday across the CO Front Range vicinity into the central High Plains, within a persistent post-frontal regime. While details are uncertain, strong to isolated severe storms cannot be ruled out, especially if any organized clustering can develop and emerge into parts of the High Plains. ...D6/Tuesday - D8/Thursday... While typical model spread is noted by Days 6-8, guidance generally depicts relatively limited severe potential into the middle of next week, as an expansive surface ridge suppresses richer low-level moisture to parts of the Gulf Coast and Texas. Some guidance shows potential for recovery by D8/Thursday across parts of the southern/central Plains, but deep-layer flow is generally forecast to remain weak to modest across the region. Read more

Day 4-8 Outlook
Day 4-8 Convective Outlook NWS Storm Prediction Center Norman OK 0309 AM CDT Thu Aug 21 2025 Valid 241200Z - 291200Z ...DISCUSSION... ...D4/Sunday - D5/Monday... A cold front that moves into the eastern CONUS on Sunday may tend to slow down, as a reinforcing shortwave moves through the base of a deep mid/upper-level trough covering the region. Scattered storms will be possible from the Northeast into the central/southern Appalachians on D4/Sunday, though with only modest instability and deep-layer shear forecast to be in place, any severe potential may remain isolated. Stronger deep-layer flow/shear is generally forecast to overspread parts of the Northeast/New England on D5/Monday, though with generally weak instability expected, severe potential is uncertain. Scattered storms will also be possible on Sunday and Monday across the CO Front Range vicinity into the central High Plains, within a persistent post-frontal regime. While details are uncertain, strong to isolated severe storms cannot be ruled out, especially if any organized clustering can develop and emerge into parts of the High Plains. ...D6/Tuesday - D8/Thursday... While typical model spread is noted by Days 6-8, guidance generally depicts relatively limited severe potential into the middle of next week, as an expansive surface ridge suppresses richer low-level moisture to parts of the Gulf Coast and Texas. Some guidance shows potential for recovery by D8/Thursday across parts of the southern/central Plains, but deep-layer flow is generally forecast to remain weak to modest across the region. Read more

SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 AM CDT Thu Aug 21 2025 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential currently appears low on Saturday. ...Parts of the Midwest/Lower Great Lakes into the south-central Plains... A mid/upper-level trough is forecast to gradually amplify across the north-central and eastern CONUS Saturday. A cold front will continue moving southeastward across parts of the Great Lakes/Midwest into the south-central Plains. Midlevel lapse rates along/ahead of the front will generally be weak, but low-level moisture will be sufficient for moderate buoyancy by afternoon. The strongest deep-layer flow/shear will located across parts of the central Great Lakes, but the convective signal in most guidance is rather sparse across this area, likely due to limited frontal convergence and very dry air aloft. The 00Z NAM is a notable outlier, depicting both a much slower front, and more substantial development along/ahead of the front during the afternoon and evening. Severe probabilities may eventually be needed if trends end up supporting more robust convection along/ahead of the front across the Midwest and Great Lakes. Farther southwest, isolated to widely scattered storms will be possible across parts of the Ozarks and south-central Plains. While a strong storm or two will be possible in this area, relatively weak deep-layer flow/shear and generally modest instability may tend to limit organized severe potential. ...CO Front Range and adjacent parts of the High Plains... Scattered thunderstorms will again be possible across parts of the CO Front Range and adjacent High Plains Saturday. While wind profiles will remain favorable for organized convection, with modestly elongated hodographs within the post-frontal regime, guidance generally depicts weaker midlevel lapse rates compared to previous days, especially across the High Plains. There may be a tendency for storms to remain confined to the higher terrain for much of the period, with uncertain severe potential. However, a marginal supercell or two with hail potential cannot be ruled out, and severe probabilities may eventually be needed for some part of this region, if trends support sufficient destabilization. ..Dean.. 08/21/2025 Read more