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SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Sat Aug 16 2025 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT ACROSS SOUTH DAKOTA AND PERHAPS ADJACENT PORTIONS OF NORTHERN NEBRASKA...NORTHEASTERN WYOMING...SOUTHEASTERN MONTANA...AND SOUTHWESTERN NORTH DAKOTA... ...SUMMARY... Scattered strong thunderstorm development, including a couple of evolving clusters posing a risk for strong to severe wind gusts, are possible today into tonight across parts of the northern Great Plains into Midwest and Great Lakes region. ...Discussion... Stronger westerlies in the northern mid-latitudes are forecast to generally remain confined to the north of the Canadian/U.S. border. Within this regime, mid-level ridging, now building across and northeast of the Canadian and adjacent northern U.S. Rockies, is likely to undergo further amplification across and east of the Canadian Prairies later today through tonight, downstream of an initially vigorous short wave trough pivoting northeastward inland of the British Columbia coast. Models indicate that larger-scale troughing across the northeastern Pacific will be maintained, as another vigorous short wave trough digs southeast of the Gulf of Alaska. Downstream of the building ridge, large-scale eastern Canadian mid-level troughing is forecast to undergo amplification, as another notable short wave trough digs across and southeast/east of the northern Ontario/southern Hudson and James Bay vicinities. Even as this occurs, it appears that modest mid-level height rises will develop across eastern portions of the northern U.S. Great Plains through the Upper Midwest and adjacent Great Lakes region later today through tonight, downstream of mid-level troughing within weak, broadly confluent mid-level flow across the Wyoming/Colorado Rockies into the western Dakotas. The remnants of an initially notable convectively generated or enhanced perturbation may dig southeastward within the northeastern periphery of the building ridging, across the Midwest/adjacent Great Lakes vicinity into Ohio Valley. However, there is considerably greater spread evident in model output concerning this feature. ...Northern Great Plains into Great Lakes/Ohio Valley... South of the westerlies, convective potential may depend largely on sub-synoptic developments with still relatively low predictability. The NAM and Rapid Refresh, among other model output, continue to suggest a notable perturbation evolving with a consolidating cluster of storms now across parts of central South Dakota into north central Nebraska. By 12Z this morning, it appears that this may be in the process of spreading east of the mid Missouri through upper Mississippi Valleys, above a boundary-layer stabilized by preceding convective activity. A conglomerate surface outflow boundary currently extends from parts of central Illinois through central Iowa and Minnesota. It seems probable that the southern flank of this boundary will undergo at least some modification/northward return into and beyond daybreak, but the extent remains unclear. Outflow impacted air across eastern Minnesota and northeastern Iowa into Wisconsin will probably be reinforced by the approaching cluster, which probably will tend to weaken while overspreading the Upper Midwest into Great Lakes region. However, depending on how quickly the boundary-layer is able to modify on the trailing flank of the reinforced outflow, it appears possible that renewed thunderstorm development and intensification could occur, and eventually grow upscale into another organizing cluster with a tendency to propagate southeastward toward the Ohio Valley. HREF output suggests that a corridor across southern Wisconsin toward areas near and south of southern Lake Michigan may need to be considered for higher severe probabilities in later outlooks for this period. However, given uncertain boundary-layer destabilization, coupled with a tendency for warming aloft/rising mid-level heights, in the presence of generally weak ambient mean flow, there seems a reasonable possibility that the corridor of higher convective potential evident in the HREF may be displaced, if not overdone. Otherwise, there remains a signal in model output that the approaching mid-level troughing could contribute to another upscale growing cluster of storms with potential to produce strong to severe wind gusts across parts of South Dakota this evening. However, this signal is more tempered than prior days. ..Kerr/Lyons.. 08/16/2025 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Sat Aug 16 2025 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT ACROSS SOUTH DAKOTA AND PERHAPS ADJACENT PORTIONS OF NORTHERN NEBRASKA...NORTHEASTERN WYOMING...SOUTHEASTERN MONTANA...AND SOUTHWESTERN NORTH DAKOTA... ...SUMMARY... Scattered strong thunderstorm development, including a couple of evolving clusters posing a risk for strong to severe wind gusts, are possible today into tonight across parts of the northern Great Plains into Midwest and Great Lakes region. ...Discussion... Stronger westerlies in the northern mid-latitudes are forecast to generally remain confined to the north of the Canadian/U.S. border. Within this regime, mid-level ridging, now building across and northeast of the Canadian and adjacent northern U.S. Rockies, is likely to undergo further amplification across and east of the Canadian Prairies later today through tonight, downstream of an initially vigorous short wave trough pivoting northeastward inland of the British Columbia coast. Models indicate that larger-scale troughing across the northeastern Pacific will be maintained, as another vigorous short wave trough digs southeast of the Gulf of Alaska. Downstream of the building ridge, large-scale eastern Canadian mid-level troughing is forecast to undergo amplification, as another notable short wave trough digs across and southeast/east of the northern Ontario/southern Hudson and James Bay vicinities. Even as this occurs, it appears that modest mid-level height rises will develop across eastern portions of the northern U.S. Great Plains through the Upper Midwest and adjacent Great Lakes region later today through tonight, downstream of mid-level troughing within weak, broadly confluent mid-level flow across the Wyoming/Colorado Rockies into the western Dakotas. The remnants of an initially notable convectively generated or enhanced perturbation may dig southeastward within the northeastern periphery of the building ridging, across the Midwest/adjacent Great Lakes vicinity into Ohio Valley. However, there is considerably greater spread evident in model output concerning this feature. ...Northern Great Plains into Great Lakes/Ohio Valley... South of the westerlies, convective potential may depend largely on sub-synoptic developments with still relatively low predictability. The NAM and Rapid Refresh, among other model output, continue to suggest a notable perturbation evolving with a consolidating cluster of storms now across parts of central South Dakota into north central Nebraska. By 12Z this morning, it appears that this may be in the process of spreading east of the mid Missouri through upper Mississippi Valleys, above a boundary-layer stabilized by preceding convective activity. A conglomerate surface outflow boundary currently extends from parts of central Illinois through central Iowa and Minnesota. It seems probable that the southern flank of this boundary will undergo at least some modification/northward return into and beyond daybreak, but the extent remains unclear. Outflow impacted air across eastern Minnesota and northeastern Iowa into Wisconsin will probably be reinforced by the approaching cluster, which probably will tend to weaken while overspreading the Upper Midwest into Great Lakes region. However, depending on how quickly the boundary-layer is able to modify on the trailing flank of the reinforced outflow, it appears possible that renewed thunderstorm development and intensification could occur, and eventually grow upscale into another organizing cluster with a tendency to propagate southeastward toward the Ohio Valley. HREF output suggests that a corridor across southern Wisconsin toward areas near and south of southern Lake Michigan may need to be considered for higher severe probabilities in later outlooks for this period. However, given uncertain boundary-layer destabilization, coupled with a tendency for warming aloft/rising mid-level heights, in the presence of generally weak ambient mean flow, there seems a reasonable possibility that the corridor of higher convective potential evident in the HREF may be displaced, if not overdone. Otherwise, there remains a signal in model output that the approaching mid-level troughing could contribute to another upscale growing cluster of storms with potential to produce strong to severe wind gusts across parts of South Dakota this evening. However, this signal is more tempered than prior days. ..Kerr/Lyons.. 08/16/2025 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Sat Aug 16 2025 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT ACROSS SOUTH DAKOTA AND PERHAPS ADJACENT PORTIONS OF NORTHERN NEBRASKA...NORTHEASTERN WYOMING...SOUTHEASTERN MONTANA...AND SOUTHWESTERN NORTH DAKOTA... ...SUMMARY... Scattered strong thunderstorm development, including a couple of evolving clusters posing a risk for strong to severe wind gusts, are possible today into tonight across parts of the northern Great Plains into Midwest and Great Lakes region. ...Discussion... Stronger westerlies in the northern mid-latitudes are forecast to generally remain confined to the north of the Canadian/U.S. border. Within this regime, mid-level ridging, now building across and northeast of the Canadian and adjacent northern U.S. Rockies, is likely to undergo further amplification across and east of the Canadian Prairies later today through tonight, downstream of an initially vigorous short wave trough pivoting northeastward inland of the British Columbia coast. Models indicate that larger-scale troughing across the northeastern Pacific will be maintained, as another vigorous short wave trough digs southeast of the Gulf of Alaska. Downstream of the building ridge, large-scale eastern Canadian mid-level troughing is forecast to undergo amplification, as another notable short wave trough digs across and southeast/east of the northern Ontario/southern Hudson and James Bay vicinities. Even as this occurs, it appears that modest mid-level height rises will develop across eastern portions of the northern U.S. Great Plains through the Upper Midwest and adjacent Great Lakes region later today through tonight, downstream of mid-level troughing within weak, broadly confluent mid-level flow across the Wyoming/Colorado Rockies into the western Dakotas. The remnants of an initially notable convectively generated or enhanced perturbation may dig southeastward within the northeastern periphery of the building ridging, across the Midwest/adjacent Great Lakes vicinity into Ohio Valley. However, there is considerably greater spread evident in model output concerning this feature. ...Northern Great Plains into Great Lakes/Ohio Valley... South of the westerlies, convective potential may depend largely on sub-synoptic developments with still relatively low predictability. The NAM and Rapid Refresh, among other model output, continue to suggest a notable perturbation evolving with a consolidating cluster of storms now across parts of central South Dakota into north central Nebraska. By 12Z this morning, it appears that this may be in the process of spreading east of the mid Missouri through upper Mississippi Valleys, above a boundary-layer stabilized by preceding convective activity. A conglomerate surface outflow boundary currently extends from parts of central Illinois through central Iowa and Minnesota. It seems probable that the southern flank of this boundary will undergo at least some modification/northward return into and beyond daybreak, but the extent remains unclear. Outflow impacted air across eastern Minnesota and northeastern Iowa into Wisconsin will probably be reinforced by the approaching cluster, which probably will tend to weaken while overspreading the Upper Midwest into Great Lakes region. However, depending on how quickly the boundary-layer is able to modify on the trailing flank of the reinforced outflow, it appears possible that renewed thunderstorm development and intensification could occur, and eventually grow upscale into another organizing cluster with a tendency to propagate southeastward toward the Ohio Valley. HREF output suggests that a corridor across southern Wisconsin toward areas near and south of southern Lake Michigan may need to be considered for higher severe probabilities in later outlooks for this period. However, given uncertain boundary-layer destabilization, coupled with a tendency for warming aloft/rising mid-level heights, in the presence of generally weak ambient mean flow, there seems a reasonable possibility that the corridor of higher convective potential evident in the HREF may be displaced, if not overdone. Otherwise, there remains a signal in model output that the approaching mid-level troughing could contribute to another upscale growing cluster of storms with potential to produce strong to severe wind gusts across parts of South Dakota this evening. However, this signal is more tempered than prior days. ..Kerr/Lyons.. 08/16/2025 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Sat Aug 16 2025 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT ACROSS SOUTH DAKOTA AND PERHAPS ADJACENT PORTIONS OF NORTHERN NEBRASKA...NORTHEASTERN WYOMING...SOUTHEASTERN MONTANA...AND SOUTHWESTERN NORTH DAKOTA... ...SUMMARY... Scattered strong thunderstorm development, including a couple of evolving clusters posing a risk for strong to severe wind gusts, are possible today into tonight across parts of the northern Great Plains into Midwest and Great Lakes region. ...Discussion... Stronger westerlies in the northern mid-latitudes are forecast to generally remain confined to the north of the Canadian/U.S. border. Within this regime, mid-level ridging, now building across and northeast of the Canadian and adjacent northern U.S. Rockies, is likely to undergo further amplification across and east of the Canadian Prairies later today through tonight, downstream of an initially vigorous short wave trough pivoting northeastward inland of the British Columbia coast. Models indicate that larger-scale troughing across the northeastern Pacific will be maintained, as another vigorous short wave trough digs southeast of the Gulf of Alaska. Downstream of the building ridge, large-scale eastern Canadian mid-level troughing is forecast to undergo amplification, as another notable short wave trough digs across and southeast/east of the northern Ontario/southern Hudson and James Bay vicinities. Even as this occurs, it appears that modest mid-level height rises will develop across eastern portions of the northern U.S. Great Plains through the Upper Midwest and adjacent Great Lakes region later today through tonight, downstream of mid-level troughing within weak, broadly confluent mid-level flow across the Wyoming/Colorado Rockies into the western Dakotas. The remnants of an initially notable convectively generated or enhanced perturbation may dig southeastward within the northeastern periphery of the building ridging, across the Midwest/adjacent Great Lakes vicinity into Ohio Valley. However, there is considerably greater spread evident in model output concerning this feature. ...Northern Great Plains into Great Lakes/Ohio Valley... South of the westerlies, convective potential may depend largely on sub-synoptic developments with still relatively low predictability. The NAM and Rapid Refresh, among other model output, continue to suggest a notable perturbation evolving with a consolidating cluster of storms now across parts of central South Dakota into north central Nebraska. By 12Z this morning, it appears that this may be in the process of spreading east of the mid Missouri through upper Mississippi Valleys, above a boundary-layer stabilized by preceding convective activity. A conglomerate surface outflow boundary currently extends from parts of central Illinois through central Iowa and Minnesota. It seems probable that the southern flank of this boundary will undergo at least some modification/northward return into and beyond daybreak, but the extent remains unclear. Outflow impacted air across eastern Minnesota and northeastern Iowa into Wisconsin will probably be reinforced by the approaching cluster, which probably will tend to weaken while overspreading the Upper Midwest into Great Lakes region. However, depending on how quickly the boundary-layer is able to modify on the trailing flank of the reinforced outflow, it appears possible that renewed thunderstorm development and intensification could occur, and eventually grow upscale into another organizing cluster with a tendency to propagate southeastward toward the Ohio Valley. HREF output suggests that a corridor across southern Wisconsin toward areas near and south of southern Lake Michigan may need to be considered for higher severe probabilities in later outlooks for this period. However, given uncertain boundary-layer destabilization, coupled with a tendency for warming aloft/rising mid-level heights, in the presence of generally weak ambient mean flow, there seems a reasonable possibility that the corridor of higher convective potential evident in the HREF may be displaced, if not overdone. Otherwise, there remains a signal in model output that the approaching mid-level troughing could contribute to another upscale growing cluster of storms with potential to produce strong to severe wind gusts across parts of South Dakota this evening. However, this signal is more tempered than prior days. ..Kerr/Lyons.. 08/16/2025 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Sat Aug 16 2025 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT ACROSS SOUTH DAKOTA AND PERHAPS ADJACENT PORTIONS OF NORTHERN NEBRASKA...NORTHEASTERN WYOMING...SOUTHEASTERN MONTANA...AND SOUTHWESTERN NORTH DAKOTA... ...SUMMARY... Scattered strong thunderstorm development, including a couple of evolving clusters posing a risk for strong to severe wind gusts, are possible today into tonight across parts of the northern Great Plains into Midwest and Great Lakes region. ...Discussion... Stronger westerlies in the northern mid-latitudes are forecast to generally remain confined to the north of the Canadian/U.S. border. Within this regime, mid-level ridging, now building across and northeast of the Canadian and adjacent northern U.S. Rockies, is likely to undergo further amplification across and east of the Canadian Prairies later today through tonight, downstream of an initially vigorous short wave trough pivoting northeastward inland of the British Columbia coast. Models indicate that larger-scale troughing across the northeastern Pacific will be maintained, as another vigorous short wave trough digs southeast of the Gulf of Alaska. Downstream of the building ridge, large-scale eastern Canadian mid-level troughing is forecast to undergo amplification, as another notable short wave trough digs across and southeast/east of the northern Ontario/southern Hudson and James Bay vicinities. Even as this occurs, it appears that modest mid-level height rises will develop across eastern portions of the northern U.S. Great Plains through the Upper Midwest and adjacent Great Lakes region later today through tonight, downstream of mid-level troughing within weak, broadly confluent mid-level flow across the Wyoming/Colorado Rockies into the western Dakotas. The remnants of an initially notable convectively generated or enhanced perturbation may dig southeastward within the northeastern periphery of the building ridging, across the Midwest/adjacent Great Lakes vicinity into Ohio Valley. However, there is considerably greater spread evident in model output concerning this feature. ...Northern Great Plains into Great Lakes/Ohio Valley... South of the westerlies, convective potential may depend largely on sub-synoptic developments with still relatively low predictability. The NAM and Rapid Refresh, among other model output, continue to suggest a notable perturbation evolving with a consolidating cluster of storms now across parts of central South Dakota into north central Nebraska. By 12Z this morning, it appears that this may be in the process of spreading east of the mid Missouri through upper Mississippi Valleys, above a boundary-layer stabilized by preceding convective activity. A conglomerate surface outflow boundary currently extends from parts of central Illinois through central Iowa and Minnesota. It seems probable that the southern flank of this boundary will undergo at least some modification/northward return into and beyond daybreak, but the extent remains unclear. Outflow impacted air across eastern Minnesota and northeastern Iowa into Wisconsin will probably be reinforced by the approaching cluster, which probably will tend to weaken while overspreading the Upper Midwest into Great Lakes region. However, depending on how quickly the boundary-layer is able to modify on the trailing flank of the reinforced outflow, it appears possible that renewed thunderstorm development and intensification could occur, and eventually grow upscale into another organizing cluster with a tendency to propagate southeastward toward the Ohio Valley. HREF output suggests that a corridor across southern Wisconsin toward areas near and south of southern Lake Michigan may need to be considered for higher severe probabilities in later outlooks for this period. However, given uncertain boundary-layer destabilization, coupled with a tendency for warming aloft/rising mid-level heights, in the presence of generally weak ambient mean flow, there seems a reasonable possibility that the corridor of higher convective potential evident in the HREF may be displaced, if not overdone. Otherwise, there remains a signal in model output that the approaching mid-level troughing could contribute to another upscale growing cluster of storms with potential to produce strong to severe wind gusts across parts of South Dakota this evening. However, this signal is more tempered than prior days. ..Kerr/Lyons.. 08/16/2025 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Sat Aug 16 2025 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT ACROSS SOUTH DAKOTA AND PERHAPS ADJACENT PORTIONS OF NORTHERN NEBRASKA...NORTHEASTERN WYOMING...SOUTHEASTERN MONTANA...AND SOUTHWESTERN NORTH DAKOTA... ...SUMMARY... Scattered strong thunderstorm development, including a couple of evolving clusters posing a risk for strong to severe wind gusts, are possible today into tonight across parts of the northern Great Plains into Midwest and Great Lakes region. ...Discussion... Stronger westerlies in the northern mid-latitudes are forecast to generally remain confined to the north of the Canadian/U.S. border. Within this regime, mid-level ridging, now building across and northeast of the Canadian and adjacent northern U.S. Rockies, is likely to undergo further amplification across and east of the Canadian Prairies later today through tonight, downstream of an initially vigorous short wave trough pivoting northeastward inland of the British Columbia coast. Models indicate that larger-scale troughing across the northeastern Pacific will be maintained, as another vigorous short wave trough digs southeast of the Gulf of Alaska. Downstream of the building ridge, large-scale eastern Canadian mid-level troughing is forecast to undergo amplification, as another notable short wave trough digs across and southeast/east of the northern Ontario/southern Hudson and James Bay vicinities. Even as this occurs, it appears that modest mid-level height rises will develop across eastern portions of the northern U.S. Great Plains through the Upper Midwest and adjacent Great Lakes region later today through tonight, downstream of mid-level troughing within weak, broadly confluent mid-level flow across the Wyoming/Colorado Rockies into the western Dakotas. The remnants of an initially notable convectively generated or enhanced perturbation may dig southeastward within the northeastern periphery of the building ridging, across the Midwest/adjacent Great Lakes vicinity into Ohio Valley. However, there is considerably greater spread evident in model output concerning this feature. ...Northern Great Plains into Great Lakes/Ohio Valley... South of the westerlies, convective potential may depend largely on sub-synoptic developments with still relatively low predictability. The NAM and Rapid Refresh, among other model output, continue to suggest a notable perturbation evolving with a consolidating cluster of storms now across parts of central South Dakota into north central Nebraska. By 12Z this morning, it appears that this may be in the process of spreading east of the mid Missouri through upper Mississippi Valleys, above a boundary-layer stabilized by preceding convective activity. A conglomerate surface outflow boundary currently extends from parts of central Illinois through central Iowa and Minnesota. It seems probable that the southern flank of this boundary will undergo at least some modification/northward return into and beyond daybreak, but the extent remains unclear. Outflow impacted air across eastern Minnesota and northeastern Iowa into Wisconsin will probably be reinforced by the approaching cluster, which probably will tend to weaken while overspreading the Upper Midwest into Great Lakes region. However, depending on how quickly the boundary-layer is able to modify on the trailing flank of the reinforced outflow, it appears possible that renewed thunderstorm development and intensification could occur, and eventually grow upscale into another organizing cluster with a tendency to propagate southeastward toward the Ohio Valley. HREF output suggests that a corridor across southern Wisconsin toward areas near and south of southern Lake Michigan may need to be considered for higher severe probabilities in later outlooks for this period. However, given uncertain boundary-layer destabilization, coupled with a tendency for warming aloft/rising mid-level heights, in the presence of generally weak ambient mean flow, there seems a reasonable possibility that the corridor of higher convective potential evident in the HREF may be displaced, if not overdone. Otherwise, there remains a signal in model output that the approaching mid-level troughing could contribute to another upscale growing cluster of storms with potential to produce strong to severe wind gusts across parts of South Dakota this evening. However, this signal is more tempered than prior days. ..Kerr/Lyons.. 08/16/2025 Read more

SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0100 AM CDT Sat Aug 16 2025 Valid 161200Z - 171200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT ACROSS SOUTH DAKOTA AND PERHAPS ADJACENT PORTIONS OF NORTHERN NEBRASKA...NORTHEASTERN WYOMING...SOUTHEASTERN MONTANA...AND SOUTHWESTERN NORTH DAKOTA... ...SUMMARY... Scattered strong thunderstorm development, including a couple of evolving clusters posing a risk for strong to severe wind gusts, are possible today into tonight across parts of the northern Great Plains into Midwest and Great Lakes region. ...Discussion... Stronger westerlies in the northern mid-latitudes are forecast to generally remain confined to the north of the Canadian/U.S. border. Within this regime, mid-level ridging, now building across and northeast of the Canadian and adjacent northern U.S. Rockies, is likely to undergo further amplification across and east of the Canadian Prairies later today through tonight, downstream of an initially vigorous short wave trough pivoting northeastward inland of the British Columbia coast. Models indicate that larger-scale troughing across the northeastern Pacific will be maintained, as another vigorous short wave trough digs southeast of the Gulf of Alaska. Downstream of the building ridge, large-scale eastern Canadian mid-level troughing is forecast to undergo amplification, as another notable short wave trough digs across and southeast/east of the northern Ontario/southern Hudson and James Bay vicinities. Even as this occurs, it appears that modest mid-level height rises will develop across eastern portions of the northern U.S. Great Plains through the Upper Midwest and adjacent Great Lakes region later today through tonight, downstream of mid-level troughing within weak, broadly confluent mid-level flow across the Wyoming/Colorado Rockies into the western Dakotas. The remnants of an initially notable convectively generated or enhanced perturbation may dig southeastward within the northeastern periphery of the building ridging, across the Midwest/adjacent Great Lakes vicinity into Ohio Valley. However, there is considerably greater spread evident in model output concerning this feature. ...Northern Great Plains into Great Lakes/Ohio Valley... South of the westerlies, convective potential may depend largely on sub-synoptic developments with still relatively low predictability. The NAM and Rapid Refresh, among other model output, continue to suggest a notable perturbation evolving with a consolidating cluster of storms now across parts of central South Dakota into north central Nebraska. By 12Z this morning, it appears that this may be in the process of spreading east of the mid Missouri through upper Mississippi Valleys, above a boundary-layer stabilized by preceding convective activity. A conglomerate surface outflow boundary currently extends from parts of central Illinois through central Iowa and Minnesota. It seems probable that the southern flank of this boundary will undergo at least some modification/northward return into and beyond daybreak, but the extent remains unclear. Outflow impacted air across eastern Minnesota and northeastern Iowa into Wisconsin will probably be reinforced by the approaching cluster, which probably will tend to weaken while overspreading the Upper Midwest into Great Lakes region. However, depending on how quickly the boundary-layer is able to modify on the trailing flank of the reinforced outflow, it appears possible that renewed thunderstorm development and intensification could occur, and eventually grow upscale into another organizing cluster with a tendency to propagate southeastward toward the Ohio Valley. HREF output suggests that a corridor across southern Wisconsin toward areas near and south of southern Lake Michigan may need to be considered for higher severe probabilities in later outlooks for this period. However, given uncertain boundary-layer destabilization, coupled with a tendency for warming aloft/rising mid-level heights, in the presence of generally weak ambient mean flow, there seems a reasonable possibility that the corridor of higher convective potential evident in the HREF may be displaced, if not overdone. Otherwise, there remains a signal in model output that the approaching mid-level troughing could contribute to another upscale growing cluster of storms with potential to produce strong to severe wind gusts across parts of South Dakota this evening. However, this signal is more tempered than prior days. ..Kerr/Lyons.. 08/16/2025 Read more

253
ABPZ20 KNHC 160502
TWOEP

Tropical Weather Outlook
NWS National Hurricane Center Miami FL
1100 PM PDT Fri Aug 15 2025

For the eastern and central North Pacific east of 180 longitude:

Tropical cyclone formation is not expected during the next 7 days.

$$
Forecaster Gibbs

MD 1960 CONCERNING SEVERE THUNDERSTORM WATCH 593... FOR SOUTHERN SOUTH DAKOTA AND NORTHERN NEBRASKA
Mesoscale Discussion 1960 NWS Storm Prediction Center Norman OK 1120 PM CDT Fri Aug 15 2025 Areas affected...southern South Dakota and northern Nebraska Concerning...Severe Thunderstorm Watch 593... Valid 160420Z - 160545Z The severe weather threat for Severe Thunderstorm Watch 593 continues. SUMMARY...Damaging thunderstorm wind potential will persist into the overnight hours. A downstream severe thunderstorm watch will likely be needed. DISCUSSION...Thunderstorms continue to slowly move east this evening across Severe Thunderstorm Watch 593. The strongest of these storms have a history of producing winds up to 70 mph. The large-scale environment remains favorable for scattered severe wind reports into the overnight hour. MUCAPE ahead of the storms remains in excess of 5000 J/kg, effective-layer shear is around 25 knots across far northern Nebraska to around 50 knots across central South Dakota, and at least modest large-scale ascent remains atop the area ahead of a subtle short-wave trough riding along the periphery of the southern Plains ridge. Current thinking is that there severe potential -- most likely wind -- will remain at least for the next couple of hours as the thunderstorms move east. At their current speeds, thunderstorms will approach the eastern edge of the ongoing severe thunderstorm watch before the watch expires at 3 AM CT. As such, an additional downstream watch will likely be needed perhaps as soon as within the hour. ..Marsh.. 08/16/2025 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...FSD...ABR...LBF...UNR...CYS... LAT...LON 42070275 42980279 42990300 43590301 43830268 43860400 44160408 44140345 44250346 44250358 44600354 44590297 45020299 45020204 45450199 45470037 44910042 44899967 44229966 43959932 43699942 43509930 43489952 42989955 42960018 42060017 42070275 MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN Read more

WW 0594 Status Updates
STATUS FOR WATCH 0594 HAS NOT BEEN ISSUED YET Read more

WW 0594 Status Updates
STATUS FOR WATCH 0594 HAS NOT BEEN ISSUED YET Read more

WW 0593 Status Updates
STATUS REPORT ON WW 593 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 15 NNE AIA TO 50 NE RAP. ..MARSH..08/16/25 ATTN...WFO...LBF...UNR...ABR... STATUS REPORT FOR WS 593 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS NEC031-161-160540- NE . NEBRASKA COUNTIES INCLUDED ARE CHERRY SHERIDAN SDC007-041-055-065-071-075-085-093-095-102-117-119-121-123-137- 160540- SD . SOUTH DAKOTA COUNTIES INCLUDED ARE BENNETT DEWEY HAAKON HUGHES JACKSON JONES LYMAN MEADE MELLETTE OGLALA LAKOTA STANLEY SULLY TODD TRIPP ZIEBACH THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

WW 0593 Status Updates
STATUS REPORT ON WW 593 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 15 NNE AIA TO 50 NE RAP. ..MARSH..08/16/25 ATTN...WFO...LBF...UNR...ABR... STATUS REPORT FOR WS 593 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS NEC031-161-160540- NE . NEBRASKA COUNTIES INCLUDED ARE CHERRY SHERIDAN SDC007-041-055-065-071-075-085-093-095-102-117-119-121-123-137- 160540- SD . SOUTH DAKOTA COUNTIES INCLUDED ARE BENNETT DEWEY HAAKON HUGHES JACKSON JONES LYMAN MEADE MELLETTE OGLALA LAKOTA STANLEY SULLY TODD TRIPP ZIEBACH THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

MD 1959 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PORTIONS OF ARIZONA
Mesoscale Discussion 1959 NWS Storm Prediction Center Norman OK 0859 PM CDT Fri Aug 15 2025 Areas affected...portions of Arizona Concerning...Severe potential...Watch unlikely Valid 160159Z - 160400Z Probability of Watch Issuance...5 percent SUMMARY...Isolated strong, potentially damaging, thunderstorm winds will be possible this afternoon into the evening. The disorganized nature of the threat should preclude the need for a watch. DISCUSSION...Thunderstorms have developed this afternoon across the higher terrain of Arizona. These storms have developed within an area being glanced by large-scale ascent associated with a short-wave trough lifting north from California into Nevada. Strong diurnal heating and modest low-level moisture have contributed to a strongly unstable environment with MUCAPE up to 3000 J/kg. Although deep-layer shear is quite meager (at or below 20 knots), precipitable water values in excess of 1.25 inches and steep low-to-mid-level lapse rates have contributed to DCAPE in excess of 1000 J/kg, and approaching 2000 J/kg in some locations. The lack of even modest cloud-layer winds will contribute to extremely slow storm motions and water-loading of updrafts. When this is combined with the magnitude of MUCAPE and DCAPE, isolated damaging downbursts are possible. However, given the disorganized nature of this potential a watch will likely not be needed. ..Marsh/Guyer.. 08/16/2025 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...TWC...FGZ...PSR...VEF... LAT...LON 30910959 30821076 32111257 34061433 34991423 35061309 34151205 32921098 32090996 31510936 31080925 30910959 MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH Read more

MD 1957 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR SOUTHERN SOUTH DAKOTA AND NORTHERN NEBRASKA
Mesoscale Discussion 1957 NWS Storm Prediction Center Norman OK 0721 PM CDT Fri Aug 15 2025 Areas affected...southern South Dakota and northern Nebraska Concerning...Severe potential...Watch possible Valid 160021Z - 160215Z Probability of Watch Issuance...60 percent SUMMARY...As thunderstorms move into the higher instability airmass, the potential for large to significant hail and damaging winds may increase. The area will be monitored through the evening for a potential severe thunderstorm watch. DISCUSSION...Thunderstorms continue to develop/increase in number across northern Nebraska and western South Dakota along the northern periphery of a southern Plains mid-level ridge. The strongest of these thunderstorms have a history of producing severe caliber winds and large hail. In particular, a severe storm moving through Sioux County Nebraska produce a measured 68 mph wind gust at the Montrose mesonet site. The number of storms in the area should continue to increase this evening as the region begins to experience increasing large-scale ascent associated with a mid-level trough rotating along the periphery of the southern Plains ridge. As the storms move east into the most unstable airmass, the degree of instability (MUCAPE > 5000 J/kg), will support large to significant sized hail and damaging wind gusts with any isolated updraft/thunderstorm. Additionally, with time, as the number of storms increases, a consolidation of cold pools may support an increased damaging wind threat. Trends will be monitored through the evening for an increase in intense thunderstorm coverage, or imminent signs of congealing cold pools. In the event that either are identified, a severe thunderstorm watch may be needed across portions of the area. ..Marsh/Guyer.. 08/16/2025 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...FSD...ABR...LBF...UNR...CYS... LAT...LON 42520354 42950383 43860327 44340210 44619978 44439857 43909817 43109849 42560019 42400216 42520354 MOST PROBABLE PEAK WIND GUST...65-80 MPH MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN Read more

WW 0593 Status Updates
STATUS FOR WATCH 0593 HAS NOT BEEN ISSUED YET Read more

WW 0593 Status Updates
STATUS FOR WATCH 0593 HAS NOT BEEN ISSUED YET Read more

MD 1958 CONCERNING SEVERE THUNDERSTORM WATCH 591... FOR PORTIONS OF EASTERN MINNESOTA AND WESTERN WISCONSIN
Mesoscale Discussion 1958 NWS Storm Prediction Center Norman OK 0724 PM CDT Fri Aug 15 2025 Areas affected...portions of eastern Minnesota and western Wisconsin Concerning...Severe Thunderstorm Watch 591... Valid 160024Z - 160200Z The severe weather threat for Severe Thunderstorm Watch 591 continues. SUMMARY...Ongoing storms have begun to cluster this evening. This trend is expected to continue, transitioning the primary threat towards damaging gusts and sporadic hail. DISCUSSION...Across WW 591, scattered strong to severe thunderstorms are ongoing and expected to continue. The initially more cellular storms have gradually coalesced into a more cluster/multicellular mode over the last 2 hours. With that transition, damaging gusts appear to be the primary threat as outflow continues to coalesce along and south of the stalled frontal boundary through eastern MN and western WI. While strong outflow should be the primary risk through the remainder of the evening, moderate deep-layer shear and buoyancy could still support sporadic hail potential with stronger but more transient updrafts. Observational and CAM trends suggest these storm will gradually move east/southeast with some severe risk through this evening. The southern extent and duration of the severe risk is somewhat uncertain as a remnant cold pool from a prior cluster is present near the IA/MN/WI border region. However, the environment should remain broadly favorable for damaging gusts and occasional hail focused on the eastern portions of WW591 for a couple more hours. ..Lyons.. 08/16/2025 ...Please see www.spc.noaa.gov for graphic product... ATTN...WFO...GRB...ARX...MPX... LAT...LON 45209374 45389289 45069100 44609038 44129020 43759050 43799130 43919205 44169294 44449338 44719369 45209374 MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 95 MPH MOST PROBABLE PEAK WIND GUST...55-70 MPH MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN Read more

WW 0591 Status Updates
STATUS REPORT ON WW 591 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 ENE MKT TO 40 NNW EAU. ..LYONS..08/16/25 ATTN...WFO...MPX...ARX... STATUS REPORT FOR WS 591 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS MNC049-131-157-160240- MN . MINNESOTA COUNTIES INCLUDED ARE GOODHUE RICE WABASHA WIC011-017-019-033-035-053-091-093-109-121-160240- WI . WISCONSIN COUNTIES INCLUDED ARE BUFFALO CHIPPEWA CLARK DUNN EAU CLAIRE JACKSON PEPIN PIERCE ST. CROIX TREMPEALEAU THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more

WW 0591 Status Updates
STATUS REPORT ON WW 591 SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 25 ENE MKT TO 40 NNW EAU. ..LYONS..08/16/25 ATTN...WFO...MPX...ARX... STATUS REPORT FOR WS 591 SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS MNC049-131-157-160240- MN . MINNESOTA COUNTIES INCLUDED ARE GOODHUE RICE WABASHA WIC011-017-019-033-035-053-091-093-109-121-160240- WI . WISCONSIN COUNTIES INCLUDED ARE BUFFALO CHIPPEWA CLARK DUNN EAU CLAIRE JACKSON PEPIN PIERCE ST. CROIX TREMPEALEAU THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES. Read more