Severe Storms

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

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

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

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 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 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 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 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 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 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