Severe Storms

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0253 PM CDT Thu Aug 21 2025 Valid 212000Z - 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. ...20z Update... No changes are needed to the D1 Convective Outlook. See previous discussion for more information. ..Thornton.. 08/21/2025 .PREV DISCUSSION... /ISSUED 1130 AM CDT Thu Aug 21 2025/ ...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. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0253 PM CDT Thu Aug 21 2025 Valid 212000Z - 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. ...20z Update... No changes are needed to the D1 Convective Outlook. See previous discussion for more information. ..Thornton.. 08/21/2025 .PREV DISCUSSION... /ISSUED 1130 AM CDT Thu Aug 21 2025/ ...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. Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0212 PM CDT Thu Aug 21 2025 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential currently appears low on Saturday. ...Central High Plains into Lower MI vicinity... The upper cyclone over Ontario will deepen modestly but mostly remain stationary, while an attendant shortwave trough deepens across the Midwest on Saturday. Stronger westerly flow will be in place across the Upper Midwest/Great Lakes as a surface cold front develops east/southeast across MI and much of the MS/OH Valleys and portions of the southern Plains. A seasonally moist airmass will be in place ahead of the cold front, with pockets of modest destabilization expected from the central High Plains into the Lower MI Vicinity. Generally weak midlevel lapse rates and poor frontal convergence will limit thunderstorm coverage, but a few storms could develop across Lower MI and perhaps parts of IN/OH. Gusty winds could accompany these storms, but overall severe potential appears low. Additional thunderstorms also will develop over higher terrain in parts of southeast WY into eastern CO, southward toward the Raton Mesa vicinity, and perhaps eastward into northern OK near the frontal boundary. The best chance for a strong storm or two appears to be over eastern CO in the post-frontal upslope regime where around 1000 J/kg MLCAPE will be present amid supercell wind profiles and steep lapse rates. Modest warming near 700 mb may suppress updraft intensity, especially amid weak large-scale ascent. If a stronger storm can be maintained off of the higher terrain, strong gusts and hail could occur. However, confidence in this scenario is low, precluding severe probabilities. ..Leitman.. 08/21/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0212 PM CDT Thu Aug 21 2025 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential currently appears low on Saturday. ...Central High Plains into Lower MI vicinity... The upper cyclone over Ontario will deepen modestly but mostly remain stationary, while an attendant shortwave trough deepens across the Midwest on Saturday. Stronger westerly flow will be in place across the Upper Midwest/Great Lakes as a surface cold front develops east/southeast across MI and much of the MS/OH Valleys and portions of the southern Plains. A seasonally moist airmass will be in place ahead of the cold front, with pockets of modest destabilization expected from the central High Plains into the Lower MI Vicinity. Generally weak midlevel lapse rates and poor frontal convergence will limit thunderstorm coverage, but a few storms could develop across Lower MI and perhaps parts of IN/OH. Gusty winds could accompany these storms, but overall severe potential appears low. Additional thunderstorms also will develop over higher terrain in parts of southeast WY into eastern CO, southward toward the Raton Mesa vicinity, and perhaps eastward into northern OK near the frontal boundary. The best chance for a strong storm or two appears to be over eastern CO in the post-frontal upslope regime where around 1000 J/kg MLCAPE will be present amid supercell wind profiles and steep lapse rates. Modest warming near 700 mb may suppress updraft intensity, especially amid weak large-scale ascent. If a stronger storm can be maintained off of the higher terrain, strong gusts and hail could occur. However, confidence in this scenario is low, precluding severe probabilities. ..Leitman.. 08/21/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0212 PM CDT Thu Aug 21 2025 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential currently appears low on Saturday. ...Central High Plains into Lower MI vicinity... The upper cyclone over Ontario will deepen modestly but mostly remain stationary, while an attendant shortwave trough deepens across the Midwest on Saturday. Stronger westerly flow will be in place across the Upper Midwest/Great Lakes as a surface cold front develops east/southeast across MI and much of the MS/OH Valleys and portions of the southern Plains. A seasonally moist airmass will be in place ahead of the cold front, with pockets of modest destabilization expected from the central High Plains into the Lower MI Vicinity. Generally weak midlevel lapse rates and poor frontal convergence will limit thunderstorm coverage, but a few storms could develop across Lower MI and perhaps parts of IN/OH. Gusty winds could accompany these storms, but overall severe potential appears low. Additional thunderstorms also will develop over higher terrain in parts of southeast WY into eastern CO, southward toward the Raton Mesa vicinity, and perhaps eastward into northern OK near the frontal boundary. The best chance for a strong storm or two appears to be over eastern CO in the post-frontal upslope regime where around 1000 J/kg MLCAPE will be present amid supercell wind profiles and steep lapse rates. Modest warming near 700 mb may suppress updraft intensity, especially amid weak large-scale ascent. If a stronger storm can be maintained off of the higher terrain, strong gusts and hail could occur. However, confidence in this scenario is low, precluding severe probabilities. ..Leitman.. 08/21/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0212 PM CDT Thu Aug 21 2025 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential currently appears low on Saturday. ...Central High Plains into Lower MI vicinity... The upper cyclone over Ontario will deepen modestly but mostly remain stationary, while an attendant shortwave trough deepens across the Midwest on Saturday. Stronger westerly flow will be in place across the Upper Midwest/Great Lakes as a surface cold front develops east/southeast across MI and much of the MS/OH Valleys and portions of the southern Plains. A seasonally moist airmass will be in place ahead of the cold front, with pockets of modest destabilization expected from the central High Plains into the Lower MI Vicinity. Generally weak midlevel lapse rates and poor frontal convergence will limit thunderstorm coverage, but a few storms could develop across Lower MI and perhaps parts of IN/OH. Gusty winds could accompany these storms, but overall severe potential appears low. Additional thunderstorms also will develop over higher terrain in parts of southeast WY into eastern CO, southward toward the Raton Mesa vicinity, and perhaps eastward into northern OK near the frontal boundary. The best chance for a strong storm or two appears to be over eastern CO in the post-frontal upslope regime where around 1000 J/kg MLCAPE will be present amid supercell wind profiles and steep lapse rates. Modest warming near 700 mb may suppress updraft intensity, especially amid weak large-scale ascent. If a stronger storm can be maintained off of the higher terrain, strong gusts and hail could occur. However, confidence in this scenario is low, precluding severe probabilities. ..Leitman.. 08/21/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0212 PM CDT Thu Aug 21 2025 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential currently appears low on Saturday. ...Central High Plains into Lower MI vicinity... The upper cyclone over Ontario will deepen modestly but mostly remain stationary, while an attendant shortwave trough deepens across the Midwest on Saturday. Stronger westerly flow will be in place across the Upper Midwest/Great Lakes as a surface cold front develops east/southeast across MI and much of the MS/OH Valleys and portions of the southern Plains. A seasonally moist airmass will be in place ahead of the cold front, with pockets of modest destabilization expected from the central High Plains into the Lower MI Vicinity. Generally weak midlevel lapse rates and poor frontal convergence will limit thunderstorm coverage, but a few storms could develop across Lower MI and perhaps parts of IN/OH. Gusty winds could accompany these storms, but overall severe potential appears low. Additional thunderstorms also will develop over higher terrain in parts of southeast WY into eastern CO, southward toward the Raton Mesa vicinity, and perhaps eastward into northern OK near the frontal boundary. The best chance for a strong storm or two appears to be over eastern CO in the post-frontal upslope regime where around 1000 J/kg MLCAPE will be present amid supercell wind profiles and steep lapse rates. Modest warming near 700 mb may suppress updraft intensity, especially amid weak large-scale ascent. If a stronger storm can be maintained off of the higher terrain, strong gusts and hail could occur. However, confidence in this scenario is low, precluding severe probabilities. ..Leitman.. 08/21/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0212 PM CDT Thu Aug 21 2025 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential currently appears low on Saturday. ...Central High Plains into Lower MI vicinity... The upper cyclone over Ontario will deepen modestly but mostly remain stationary, while an attendant shortwave trough deepens across the Midwest on Saturday. Stronger westerly flow will be in place across the Upper Midwest/Great Lakes as a surface cold front develops east/southeast across MI and much of the MS/OH Valleys and portions of the southern Plains. A seasonally moist airmass will be in place ahead of the cold front, with pockets of modest destabilization expected from the central High Plains into the Lower MI Vicinity. Generally weak midlevel lapse rates and poor frontal convergence will limit thunderstorm coverage, but a few storms could develop across Lower MI and perhaps parts of IN/OH. Gusty winds could accompany these storms, but overall severe potential appears low. Additional thunderstorms also will develop over higher terrain in parts of southeast WY into eastern CO, southward toward the Raton Mesa vicinity, and perhaps eastward into northern OK near the frontal boundary. The best chance for a strong storm or two appears to be over eastern CO in the post-frontal upslope regime where around 1000 J/kg MLCAPE will be present amid supercell wind profiles and steep lapse rates. Modest warming near 700 mb may suppress updraft intensity, especially amid weak large-scale ascent. If a stronger storm can be maintained off of the higher terrain, strong gusts and hail could occur. However, confidence in this scenario is low, precluding severe probabilities. ..Leitman.. 08/21/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0212 PM CDT Thu Aug 21 2025 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential currently appears low on Saturday. ...Central High Plains into Lower MI vicinity... The upper cyclone over Ontario will deepen modestly but mostly remain stationary, while an attendant shortwave trough deepens across the Midwest on Saturday. Stronger westerly flow will be in place across the Upper Midwest/Great Lakes as a surface cold front develops east/southeast across MI and much of the MS/OH Valleys and portions of the southern Plains. A seasonally moist airmass will be in place ahead of the cold front, with pockets of modest destabilization expected from the central High Plains into the Lower MI Vicinity. Generally weak midlevel lapse rates and poor frontal convergence will limit thunderstorm coverage, but a few storms could develop across Lower MI and perhaps parts of IN/OH. Gusty winds could accompany these storms, but overall severe potential appears low. Additional thunderstorms also will develop over higher terrain in parts of southeast WY into eastern CO, southward toward the Raton Mesa vicinity, and perhaps eastward into northern OK near the frontal boundary. The best chance for a strong storm or two appears to be over eastern CO in the post-frontal upslope regime where around 1000 J/kg MLCAPE will be present amid supercell wind profiles and steep lapse rates. Modest warming near 700 mb may suppress updraft intensity, especially amid weak large-scale ascent. If a stronger storm can be maintained off of the higher terrain, strong gusts and hail could occur. However, confidence in this scenario is low, precluding severe probabilities. ..Leitman.. 08/21/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0212 PM CDT Thu Aug 21 2025 Valid 231200Z - 241200Z ...NO SEVERE THUNDERSTORM AREAS FORECAST... ...SUMMARY... Severe thunderstorm potential currently appears low on Saturday. ...Central High Plains into Lower MI vicinity... The upper cyclone over Ontario will deepen modestly but mostly remain stationary, while an attendant shortwave trough deepens across the Midwest on Saturday. Stronger westerly flow will be in place across the Upper Midwest/Great Lakes as a surface cold front develops east/southeast across MI and much of the MS/OH Valleys and portions of the southern Plains. A seasonally moist airmass will be in place ahead of the cold front, with pockets of modest destabilization expected from the central High Plains into the Lower MI Vicinity. Generally weak midlevel lapse rates and poor frontal convergence will limit thunderstorm coverage, but a few storms could develop across Lower MI and perhaps parts of IN/OH. Gusty winds could accompany these storms, but overall severe potential appears low. Additional thunderstorms also will develop over higher terrain in parts of southeast WY into eastern CO, southward toward the Raton Mesa vicinity, and perhaps eastward into northern OK near the frontal boundary. The best chance for a strong storm or two appears to be over eastern CO in the post-frontal upslope regime where around 1000 J/kg MLCAPE will be present amid supercell wind profiles and steep lapse rates. Modest warming near 700 mb may suppress updraft intensity, especially amid weak large-scale ascent. If a stronger storm can be maintained off of the higher terrain, strong gusts and hail could occur. However, confidence in this scenario is low, precluding severe probabilities. ..Leitman.. 08/21/2025 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0144 PM CDT Thu Aug 21 2025 Valid 221200Z - 231200Z The IsoDryT areas were merged and expanded. Scattered mixed wet/dry thunderstorms are likely across much of Utah and western Colorado, with PWAT values of 0.7-0.9" and storm motions of 10-20 knots. Wetting rain is likely in some areas due to the increasing monsoonal moisture and training of storms. However, due to the very/record dry fuels, potential for deep pyroconvection on active large fires, and anticipated locally elevated conditions, the IsoDryT was expanded. Isolated mixed wet/dry thunderstorms are possible in portions of the Peninsular Ranges of southern California and into the Mojave, and isolated high-based showers with embedded thunderstorms are also possible in southern California overnight. An Elevated area was introduced for portions of eastern New England. Dry/breezy northerly winds are likely as Hurricane Erin passes offshore and fuels are receptive, especially in Maine, where fire activity has increased recently. Hot/dry/unstable/breezy conditions are expected along the thermal trough extending from southern California into the Northwest. Higher probabilities of the Hot, Dry, Windy Index exceeding the 95th percentile and locally elevated winds/RH are forecast in portions of California, Oregon, and Washington near the thermal trough. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 21 2025/ ...Synopsis... As the upper ridge persist over the West, several subtropical perturbations will arrive from the south, ushering in another surge of monsoon moisture. Isolated thunderstorms are likely across the southern Sierra and into parts of the Great Basin Friday. With very warm surface temperatures and dry sub-cloud layers, little wetting rainfall is expected. This should allow for isolated dry lightning atop receptive fuel mainly over portions of California and Nevada where fuels are most receptive. Some localized dry and breezy winds may also occur outside of the thunderstorms over the central great Basin Friday. Over the southern Great Basin and Southwest, higher PWATs near 1 inch are expected. Isolated to widely scattered thunderstorms are likely through the afternoon. However, a wetter storm mode is more probable across northern Arizona, southern Utah and western Colorado, where fuels are also less receptive. ...California... Isolated thunderstorms are likely in portions of southern California mountains and over the Mojave. A wetter mode is expected with max PWATs near 1.2 to 1.3 inches and little in the way of steering flow. However, cloud bases are likely to be over 3-km with a hot/dry sub-cloud layer limiting some precipitation efficiency. Sporadic dry strikes re possible given the degree of extreme heat and dry fuels but coverage is not expected to reach 10% or greater. Additionally, very hot, dry and unstable conditions may support plume dominated fire behavior with existing large fires. ...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 0144 PM CDT Thu Aug 21 2025 Valid 221200Z - 231200Z The IsoDryT areas were merged and expanded. Scattered mixed wet/dry thunderstorms are likely across much of Utah and western Colorado, with PWAT values of 0.7-0.9" and storm motions of 10-20 knots. Wetting rain is likely in some areas due to the increasing monsoonal moisture and training of storms. However, due to the very/record dry fuels, potential for deep pyroconvection on active large fires, and anticipated locally elevated conditions, the IsoDryT was expanded. Isolated mixed wet/dry thunderstorms are possible in portions of the Peninsular Ranges of southern California and into the Mojave, and isolated high-based showers with embedded thunderstorms are also possible in southern California overnight. An Elevated area was introduced for portions of eastern New England. Dry/breezy northerly winds are likely as Hurricane Erin passes offshore and fuels are receptive, especially in Maine, where fire activity has increased recently. Hot/dry/unstable/breezy conditions are expected along the thermal trough extending from southern California into the Northwest. Higher probabilities of the Hot, Dry, Windy Index exceeding the 95th percentile and locally elevated winds/RH are forecast in portions of California, Oregon, and Washington near the thermal trough. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 21 2025/ ...Synopsis... As the upper ridge persist over the West, several subtropical perturbations will arrive from the south, ushering in another surge of monsoon moisture. Isolated thunderstorms are likely across the southern Sierra and into parts of the Great Basin Friday. With very warm surface temperatures and dry sub-cloud layers, little wetting rainfall is expected. This should allow for isolated dry lightning atop receptive fuel mainly over portions of California and Nevada where fuels are most receptive. Some localized dry and breezy winds may also occur outside of the thunderstorms over the central great Basin Friday. Over the southern Great Basin and Southwest, higher PWATs near 1 inch are expected. Isolated to widely scattered thunderstorms are likely through the afternoon. However, a wetter storm mode is more probable across northern Arizona, southern Utah and western Colorado, where fuels are also less receptive. ...California... Isolated thunderstorms are likely in portions of southern California mountains and over the Mojave. A wetter mode is expected with max PWATs near 1.2 to 1.3 inches and little in the way of steering flow. However, cloud bases are likely to be over 3-km with a hot/dry sub-cloud layer limiting some precipitation efficiency. Sporadic dry strikes re possible given the degree of extreme heat and dry fuels but coverage is not expected to reach 10% or greater. Additionally, very hot, dry and unstable conditions may support plume dominated fire behavior with existing large fires. ...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 0144 PM CDT Thu Aug 21 2025 Valid 221200Z - 231200Z The IsoDryT areas were merged and expanded. Scattered mixed wet/dry thunderstorms are likely across much of Utah and western Colorado, with PWAT values of 0.7-0.9" and storm motions of 10-20 knots. Wetting rain is likely in some areas due to the increasing monsoonal moisture and training of storms. However, due to the very/record dry fuels, potential for deep pyroconvection on active large fires, and anticipated locally elevated conditions, the IsoDryT was expanded. Isolated mixed wet/dry thunderstorms are possible in portions of the Peninsular Ranges of southern California and into the Mojave, and isolated high-based showers with embedded thunderstorms are also possible in southern California overnight. An Elevated area was introduced for portions of eastern New England. Dry/breezy northerly winds are likely as Hurricane Erin passes offshore and fuels are receptive, especially in Maine, where fire activity has increased recently. Hot/dry/unstable/breezy conditions are expected along the thermal trough extending from southern California into the Northwest. Higher probabilities of the Hot, Dry, Windy Index exceeding the 95th percentile and locally elevated winds/RH are forecast in portions of California, Oregon, and Washington near the thermal trough. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 21 2025/ ...Synopsis... As the upper ridge persist over the West, several subtropical perturbations will arrive from the south, ushering in another surge of monsoon moisture. Isolated thunderstorms are likely across the southern Sierra and into parts of the Great Basin Friday. With very warm surface temperatures and dry sub-cloud layers, little wetting rainfall is expected. This should allow for isolated dry lightning atop receptive fuel mainly over portions of California and Nevada where fuels are most receptive. Some localized dry and breezy winds may also occur outside of the thunderstorms over the central great Basin Friday. Over the southern Great Basin and Southwest, higher PWATs near 1 inch are expected. Isolated to widely scattered thunderstorms are likely through the afternoon. However, a wetter storm mode is more probable across northern Arizona, southern Utah and western Colorado, where fuels are also less receptive. ...California... Isolated thunderstorms are likely in portions of southern California mountains and over the Mojave. A wetter mode is expected with max PWATs near 1.2 to 1.3 inches and little in the way of steering flow. However, cloud bases are likely to be over 3-km with a hot/dry sub-cloud layer limiting some precipitation efficiency. Sporadic dry strikes re possible given the degree of extreme heat and dry fuels but coverage is not expected to reach 10% or greater. Additionally, very hot, dry and unstable conditions may support plume dominated fire behavior with existing large fires. ...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 0144 PM CDT Thu Aug 21 2025 Valid 221200Z - 231200Z The IsoDryT areas were merged and expanded. Scattered mixed wet/dry thunderstorms are likely across much of Utah and western Colorado, with PWAT values of 0.7-0.9" and storm motions of 10-20 knots. Wetting rain is likely in some areas due to the increasing monsoonal moisture and training of storms. However, due to the very/record dry fuels, potential for deep pyroconvection on active large fires, and anticipated locally elevated conditions, the IsoDryT was expanded. Isolated mixed wet/dry thunderstorms are possible in portions of the Peninsular Ranges of southern California and into the Mojave, and isolated high-based showers with embedded thunderstorms are also possible in southern California overnight. An Elevated area was introduced for portions of eastern New England. Dry/breezy northerly winds are likely as Hurricane Erin passes offshore and fuels are receptive, especially in Maine, where fire activity has increased recently. Hot/dry/unstable/breezy conditions are expected along the thermal trough extending from southern California into the Northwest. Higher probabilities of the Hot, Dry, Windy Index exceeding the 95th percentile and locally elevated winds/RH are forecast in portions of California, Oregon, and Washington near the thermal trough. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 21 2025/ ...Synopsis... As the upper ridge persist over the West, several subtropical perturbations will arrive from the south, ushering in another surge of monsoon moisture. Isolated thunderstorms are likely across the southern Sierra and into parts of the Great Basin Friday. With very warm surface temperatures and dry sub-cloud layers, little wetting rainfall is expected. This should allow for isolated dry lightning atop receptive fuel mainly over portions of California and Nevada where fuels are most receptive. Some localized dry and breezy winds may also occur outside of the thunderstorms over the central great Basin Friday. Over the southern Great Basin and Southwest, higher PWATs near 1 inch are expected. Isolated to widely scattered thunderstorms are likely through the afternoon. However, a wetter storm mode is more probable across northern Arizona, southern Utah and western Colorado, where fuels are also less receptive. ...California... Isolated thunderstorms are likely in portions of southern California mountains and over the Mojave. A wetter mode is expected with max PWATs near 1.2 to 1.3 inches and little in the way of steering flow. However, cloud bases are likely to be over 3-km with a hot/dry sub-cloud layer limiting some precipitation efficiency. Sporadic dry strikes re possible given the degree of extreme heat and dry fuels but coverage is not expected to reach 10% or greater. Additionally, very hot, dry and unstable conditions may support plume dominated fire behavior with existing large fires. ...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 0144 PM CDT Thu Aug 21 2025 Valid 221200Z - 231200Z The IsoDryT areas were merged and expanded. Scattered mixed wet/dry thunderstorms are likely across much of Utah and western Colorado, with PWAT values of 0.7-0.9" and storm motions of 10-20 knots. Wetting rain is likely in some areas due to the increasing monsoonal moisture and training of storms. However, due to the very/record dry fuels, potential for deep pyroconvection on active large fires, and anticipated locally elevated conditions, the IsoDryT was expanded. Isolated mixed wet/dry thunderstorms are possible in portions of the Peninsular Ranges of southern California and into the Mojave, and isolated high-based showers with embedded thunderstorms are also possible in southern California overnight. An Elevated area was introduced for portions of eastern New England. Dry/breezy northerly winds are likely as Hurricane Erin passes offshore and fuels are receptive, especially in Maine, where fire activity has increased recently. Hot/dry/unstable/breezy conditions are expected along the thermal trough extending from southern California into the Northwest. Higher probabilities of the Hot, Dry, Windy Index exceeding the 95th percentile and locally elevated winds/RH are forecast in portions of California, Oregon, and Washington near the thermal trough. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 21 2025/ ...Synopsis... As the upper ridge persist over the West, several subtropical perturbations will arrive from the south, ushering in another surge of monsoon moisture. Isolated thunderstorms are likely across the southern Sierra and into parts of the Great Basin Friday. With very warm surface temperatures and dry sub-cloud layers, little wetting rainfall is expected. This should allow for isolated dry lightning atop receptive fuel mainly over portions of California and Nevada where fuels are most receptive. Some localized dry and breezy winds may also occur outside of the thunderstorms over the central great Basin Friday. Over the southern Great Basin and Southwest, higher PWATs near 1 inch are expected. Isolated to widely scattered thunderstorms are likely through the afternoon. However, a wetter storm mode is more probable across northern Arizona, southern Utah and western Colorado, where fuels are also less receptive. ...California... Isolated thunderstorms are likely in portions of southern California mountains and over the Mojave. A wetter mode is expected with max PWATs near 1.2 to 1.3 inches and little in the way of steering flow. However, cloud bases are likely to be over 3-km with a hot/dry sub-cloud layer limiting some precipitation efficiency. Sporadic dry strikes re possible given the degree of extreme heat and dry fuels but coverage is not expected to reach 10% or greater. Additionally, very hot, dry and unstable conditions may support plume dominated fire behavior with existing large fires. ...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 0144 PM CDT Thu Aug 21 2025 Valid 221200Z - 231200Z The IsoDryT areas were merged and expanded. Scattered mixed wet/dry thunderstorms are likely across much of Utah and western Colorado, with PWAT values of 0.7-0.9" and storm motions of 10-20 knots. Wetting rain is likely in some areas due to the increasing monsoonal moisture and training of storms. However, due to the very/record dry fuels, potential for deep pyroconvection on active large fires, and anticipated locally elevated conditions, the IsoDryT was expanded. Isolated mixed wet/dry thunderstorms are possible in portions of the Peninsular Ranges of southern California and into the Mojave, and isolated high-based showers with embedded thunderstorms are also possible in southern California overnight. An Elevated area was introduced for portions of eastern New England. Dry/breezy northerly winds are likely as Hurricane Erin passes offshore and fuels are receptive, especially in Maine, where fire activity has increased recently. Hot/dry/unstable/breezy conditions are expected along the thermal trough extending from southern California into the Northwest. Higher probabilities of the Hot, Dry, Windy Index exceeding the 95th percentile and locally elevated winds/RH are forecast in portions of California, Oregon, and Washington near the thermal trough. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 21 2025/ ...Synopsis... As the upper ridge persist over the West, several subtropical perturbations will arrive from the south, ushering in another surge of monsoon moisture. Isolated thunderstorms are likely across the southern Sierra and into parts of the Great Basin Friday. With very warm surface temperatures and dry sub-cloud layers, little wetting rainfall is expected. This should allow for isolated dry lightning atop receptive fuel mainly over portions of California and Nevada where fuels are most receptive. Some localized dry and breezy winds may also occur outside of the thunderstorms over the central great Basin Friday. Over the southern Great Basin and Southwest, higher PWATs near 1 inch are expected. Isolated to widely scattered thunderstorms are likely through the afternoon. However, a wetter storm mode is more probable across northern Arizona, southern Utah and western Colorado, where fuels are also less receptive. ...California... Isolated thunderstorms are likely in portions of southern California mountains and over the Mojave. A wetter mode is expected with max PWATs near 1.2 to 1.3 inches and little in the way of steering flow. However, cloud bases are likely to be over 3-km with a hot/dry sub-cloud layer limiting some precipitation efficiency. Sporadic dry strikes re possible given the degree of extreme heat and dry fuels but coverage is not expected to reach 10% or greater. Additionally, very hot, dry and unstable conditions may support plume dominated fire behavior with existing large fires. ...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 0144 PM CDT Thu Aug 21 2025 Valid 221200Z - 231200Z The IsoDryT areas were merged and expanded. Scattered mixed wet/dry thunderstorms are likely across much of Utah and western Colorado, with PWAT values of 0.7-0.9" and storm motions of 10-20 knots. Wetting rain is likely in some areas due to the increasing monsoonal moisture and training of storms. However, due to the very/record dry fuels, potential for deep pyroconvection on active large fires, and anticipated locally elevated conditions, the IsoDryT was expanded. Isolated mixed wet/dry thunderstorms are possible in portions of the Peninsular Ranges of southern California and into the Mojave, and isolated high-based showers with embedded thunderstorms are also possible in southern California overnight. An Elevated area was introduced for portions of eastern New England. Dry/breezy northerly winds are likely as Hurricane Erin passes offshore and fuels are receptive, especially in Maine, where fire activity has increased recently. Hot/dry/unstable/breezy conditions are expected along the thermal trough extending from southern California into the Northwest. Higher probabilities of the Hot, Dry, Windy Index exceeding the 95th percentile and locally elevated winds/RH are forecast in portions of California, Oregon, and Washington near the thermal trough. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 21 2025/ ...Synopsis... As the upper ridge persist over the West, several subtropical perturbations will arrive from the south, ushering in another surge of monsoon moisture. Isolated thunderstorms are likely across the southern Sierra and into parts of the Great Basin Friday. With very warm surface temperatures and dry sub-cloud layers, little wetting rainfall is expected. This should allow for isolated dry lightning atop receptive fuel mainly over portions of California and Nevada where fuels are most receptive. Some localized dry and breezy winds may also occur outside of the thunderstorms over the central great Basin Friday. Over the southern Great Basin and Southwest, higher PWATs near 1 inch are expected. Isolated to widely scattered thunderstorms are likely through the afternoon. However, a wetter storm mode is more probable across northern Arizona, southern Utah and western Colorado, where fuels are also less receptive. ...California... Isolated thunderstorms are likely in portions of southern California mountains and over the Mojave. A wetter mode is expected with max PWATs near 1.2 to 1.3 inches and little in the way of steering flow. However, cloud bases are likely to be over 3-km with a hot/dry sub-cloud layer limiting some precipitation efficiency. Sporadic dry strikes re possible given the degree of extreme heat and dry fuels but coverage is not expected to reach 10% or greater. Additionally, very hot, dry and unstable conditions may support plume dominated fire behavior with existing large fires. ...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 0144 PM CDT Thu Aug 21 2025 Valid 221200Z - 231200Z The IsoDryT areas were merged and expanded. Scattered mixed wet/dry thunderstorms are likely across much of Utah and western Colorado, with PWAT values of 0.7-0.9" and storm motions of 10-20 knots. Wetting rain is likely in some areas due to the increasing monsoonal moisture and training of storms. However, due to the very/record dry fuels, potential for deep pyroconvection on active large fires, and anticipated locally elevated conditions, the IsoDryT was expanded. Isolated mixed wet/dry thunderstorms are possible in portions of the Peninsular Ranges of southern California and into the Mojave, and isolated high-based showers with embedded thunderstorms are also possible in southern California overnight. An Elevated area was introduced for portions of eastern New England. Dry/breezy northerly winds are likely as Hurricane Erin passes offshore and fuels are receptive, especially in Maine, where fire activity has increased recently. Hot/dry/unstable/breezy conditions are expected along the thermal trough extending from southern California into the Northwest. Higher probabilities of the Hot, Dry, Windy Index exceeding the 95th percentile and locally elevated winds/RH are forecast in portions of California, Oregon, and Washington near the thermal trough. ..Nauslar.. 08/21/2025 .PREV DISCUSSION... /ISSUED 0157 AM CDT Thu Aug 21 2025/ ...Synopsis... As the upper ridge persist over the West, several subtropical perturbations will arrive from the south, ushering in another surge of monsoon moisture. Isolated thunderstorms are likely across the southern Sierra and into parts of the Great Basin Friday. With very warm surface temperatures and dry sub-cloud layers, little wetting rainfall is expected. This should allow for isolated dry lightning atop receptive fuel mainly over portions of California and Nevada where fuels are most receptive. Some localized dry and breezy winds may also occur outside of the thunderstorms over the central great Basin Friday. Over the southern Great Basin and Southwest, higher PWATs near 1 inch are expected. Isolated to widely scattered thunderstorms are likely through the afternoon. However, a wetter storm mode is more probable across northern Arizona, southern Utah and western Colorado, where fuels are also less receptive. ...California... Isolated thunderstorms are likely in portions of southern California mountains and over the Mojave. A wetter mode is expected with max PWATs near 1.2 to 1.3 inches and little in the way of steering flow. However, cloud bases are likely to be over 3-km with a hot/dry sub-cloud layer limiting some precipitation efficiency. Sporadic dry strikes re possible given the degree of extreme heat and dry fuels but coverage is not expected to reach 10% or greater. Additionally, very hot, dry and unstable conditions may support plume dominated fire behavior with existing large fires. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1209 PM CDT Thu Aug 21 2025 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTHERN/CENTRAL HIGH PLAINS TO THE UPPER MIDWEST...AND OVER SOUTHWEST AZ AND FAR SOUTHEAST CA... ...SUMMARY... Strong to locally severe thunderstorms are possible Friday from parts of the central and northern High Plains into the Upper Midwest, and across southwest Arizona into far southeast California. ...Northern/Central High Plains to Upper Midwest... An upper cyclone centered over Manitoba Friday morning and its attendant shortwave trough extending into the northern Plains will develop southeast into Ontario and Upper Midwest through early Saturday. At the surface, a trailing cold front will spread east/southeast across the region, extending from northeast MN into southwest NE/northeast CO by 00z, before continuing on to portions of the U.P. of MI to southwest KS/southeast CO by Saturday morning. Ahead of the front, seasonal boundary layer moisture will be in place, and pockets of weak to moderate destabilization are forecast. However, lapse rates are generally expected to remain modest across the Upper Midwest, which may limit updraft intensity somewhat. Additionally, remnant convection from the Day 1/Thu period may be ongoing across parts of MN at the beginning of the period. The extent of this activity and associated cloud cover may temper stronger heating/destabilization as well. Nevertheless, as large-scale ascent increasing with the approach of the upper trough and along the surface cold front, isolated strong to severe storms may develop during the afternoon and evening, posing a risk for strong gusts and marginal hail. Further southwest into the High Plains, the post-frontal upslope flow regime will likely result in isolated thunderstorm development across parts of western WY/CO, with convection spreading into parts of SD/NE. Steeper lapse rates and a deeper, mixed boundary layer may support strong/severe gusts and isolated hail. ...Southwest AZ into far southeast CA... A surge of monsoonal moisture is expected over the region on Friday amid steep lapse rates and hot boundary layer conditions. This should support modest destabilization, with strong DCAPE near 1500 J/kg noted in forecast soundings. Around 20-35 kt east/northeast mid/upper flow atop weak westerly low-level winds will foster around 30-40 kt effective shear magnitudes. Initial thunderstorm activity is expected to develop over higher terrain. Most CAMs guidance and HREF calibrated/ML guidance suggest sufficient clustering and surging outflow will move east/southeast across southwest AZ/far southeast CA. Given the deeply mixed boundary layer/steep lapse rates, have introduced a Marginal risk (level 1 of 5) for severe wind gust potential across the lower deserts/Lower CO Valley vicinity. ..Leitman.. 08/21/2025 Read more

SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1209 PM CDT Thu Aug 21 2025 Valid 221200Z - 231200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF THE NORTHERN/CENTRAL HIGH PLAINS TO THE UPPER MIDWEST...AND OVER SOUTHWEST AZ AND FAR SOUTHEAST CA... ...SUMMARY... Strong to locally severe thunderstorms are possible Friday from parts of the central and northern High Plains into the Upper Midwest, and across southwest Arizona into far southeast California. ...Northern/Central High Plains to Upper Midwest... An upper cyclone centered over Manitoba Friday morning and its attendant shortwave trough extending into the northern Plains will develop southeast into Ontario and Upper Midwest through early Saturday. At the surface, a trailing cold front will spread east/southeast across the region, extending from northeast MN into southwest NE/northeast CO by 00z, before continuing on to portions of the U.P. of MI to southwest KS/southeast CO by Saturday morning. Ahead of the front, seasonal boundary layer moisture will be in place, and pockets of weak to moderate destabilization are forecast. However, lapse rates are generally expected to remain modest across the Upper Midwest, which may limit updraft intensity somewhat. Additionally, remnant convection from the Day 1/Thu period may be ongoing across parts of MN at the beginning of the period. The extent of this activity and associated cloud cover may temper stronger heating/destabilization as well. Nevertheless, as large-scale ascent increasing with the approach of the upper trough and along the surface cold front, isolated strong to severe storms may develop during the afternoon and evening, posing a risk for strong gusts and marginal hail. Further southwest into the High Plains, the post-frontal upslope flow regime will likely result in isolated thunderstorm development across parts of western WY/CO, with convection spreading into parts of SD/NE. Steeper lapse rates and a deeper, mixed boundary layer may support strong/severe gusts and isolated hail. ...Southwest AZ into far southeast CA... A surge of monsoonal moisture is expected over the region on Friday amid steep lapse rates and hot boundary layer conditions. This should support modest destabilization, with strong DCAPE near 1500 J/kg noted in forecast soundings. Around 20-35 kt east/northeast mid/upper flow atop weak westerly low-level winds will foster around 30-40 kt effective shear magnitudes. Initial thunderstorm activity is expected to develop over higher terrain. Most CAMs guidance and HREF calibrated/ML guidance suggest sufficient clustering and surging outflow will move east/southeast across southwest AZ/far southeast CA. Given the deeply mixed boundary layer/steep lapse rates, have introduced a Marginal risk (level 1 of 5) for severe wind gust potential across the lower deserts/Lower CO Valley vicinity. ..Leitman.. 08/21/2025 Read more