Severe Storms

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Thu Sep 04 2025 Valid 042000Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF NEW YORK...TO THE MID ATLANTIC...SOUTHERN APPALACHIANS AND MID MISSOURI VALLEY... ...SUMMARY... Isolated damaging gusts remain possible across parts of New York to the Mid-Atlantic and Southern Appalachians through early this evening. Isolated severe gusts are also possible across parts of the mid Missouri Valley late this afternoon and early evening. ...20z Update Mid Atlantic and southern Appalachians... Several clusters of strong to severe thunderstorms have matured and are expected to continue through early this evening along and ahead of the slow-moving cold front from the Mid Atlantic southward. Despite poor mid-level lapse rates, heating of the modestly moist air mass is supporting around 500-1000 J/kg of MLCAPE, sufficient for a few stronger updrafts. As convection gradually increases in coverage through the remainder of this afternoon, clustering and 30-40 kt of mid-level flow will continue to support isolated damaging gust potential into early this evening. Some hail remains possible with the more cellular elements, especially father southwest over the eastern TN Valley where storm coverage should remain more isolated. The primary change was to align the western edge of the MRGL and severe probabilities with current frontal position, and shift them slightly east for ongoing storms on the border of NC and southern VA. ...New York... As the line of showers and weak thunderstorms continues eastward along the front, occasional damaging gusts remain possible owing to mixing of stronger mid-level flow downward this afternoon. Some heating, but marginal surface moisture should keep buoyancy and the resulting updrafts weak. With MLCAPE generally less than 500 J/kg, showers and storms should steadily weaken with the loss of diurnal heating. The MRGL risk area has been trimmed behind the ongoing line. Otherwise, the prior outlook remains unchanged, see the previous discussion. ..Lyons.. 09/04/2025 .PREV DISCUSSION... /ISSUED 1124 AM CDT Thu Sep 04 2025/ ...New York into the Mid-Atlantic and Tennessee Valley... A closed mid/upper-level low will remain centered over Ontario today. Multiple mid-level perturbations will rotate around this feature through the period, including a shortwave trough forecast to advance generally east-northeastward across parts of the central Appalachians/Mid-Atlantic into the Northeast. Showers and thunderstorms are ongoing mainly ahead of a surface cold front from parts of western NY southward to the TN Valley in a low/mid-level moisture plume. Generally clear skies ahead of this activity should allow for ample daytime heating of a modestly moistened low-level airmass. Even so, 12Z observed soundings from BUF, IAD, and RNK/GSO show rather poor mid-level lapse rates, which will likely hinder updraft strength even as weak instability develops this afternoon with continued diurnal heating. Modestly enhanced southwesterly low/mid-level flow should still aid in some thunderstorm organization even with the apparent thermodynamic limitations, with multicells the dominant convective mode. Wherever low-level lapse rates can become steepened, a risk for at least isolated damaging winds remains apparent. Some hail may also occur with the strongest cores across parts of the TN Valley/southern Appalachians where locally greater instability should be present this afternoon. The Marginal Risk has been adjusted for ongoing trends, but the potential for a more focused corridor of scattered severe/damaging winds remains unclear. ...Mid Missouri Valley... A mid-level shortwave trough and attendant strong speed maximum will move quickly southeastward today from central Canada and the northern Plains towards the mid MO Valley and vicinity. Pronounced ascent associated with this jet should encourage convection to develop by late this afternoon across parts of eastern SD and vicinity. While low-level moisture and MLCAPE are both expected to remain very limited, enhanced low/mid-level northwesterly flow may still support some risk for severe gusts with any low-topped convection that can develop and spread quickly southeastward before weakening this evening with the loss of daytime heating. ...Kansas... A sharp cold front will sweep southward across the central Plains tonight. Elevated convection should form to the cool side of this boundary late tonight through early Friday morning given sufficient MUCAPE. Locally strong surface gusts and small hail may accompany this activity amid robust low-level northerlies, but the overall severe potential should remain fairly low given the tendency for convection to be mostly elevated. ...Arizona/Lower Colorado River Valley... Thunderstorms should develop again today across parts of central/southern AZ and the lower CO River Valley, beneath weak mid-level flow and on the periphery of increasing mid-level moisture associated with Tropical Storm Lorena. Weak shear should keep thunderstorms mostly disorganized, but occasional strong/gusty winds may occur where low-level lapse rates can become steepened. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Thu Sep 04 2025 Valid 042000Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF NEW YORK...TO THE MID ATLANTIC...SOUTHERN APPALACHIANS AND MID MISSOURI VALLEY... ...SUMMARY... Isolated damaging gusts remain possible across parts of New York to the Mid-Atlantic and Southern Appalachians through early this evening. Isolated severe gusts are also possible across parts of the mid Missouri Valley late this afternoon and early evening. ...20z Update Mid Atlantic and southern Appalachians... Several clusters of strong to severe thunderstorms have matured and are expected to continue through early this evening along and ahead of the slow-moving cold front from the Mid Atlantic southward. Despite poor mid-level lapse rates, heating of the modestly moist air mass is supporting around 500-1000 J/kg of MLCAPE, sufficient for a few stronger updrafts. As convection gradually increases in coverage through the remainder of this afternoon, clustering and 30-40 kt of mid-level flow will continue to support isolated damaging gust potential into early this evening. Some hail remains possible with the more cellular elements, especially father southwest over the eastern TN Valley where storm coverage should remain more isolated. The primary change was to align the western edge of the MRGL and severe probabilities with current frontal position, and shift them slightly east for ongoing storms on the border of NC and southern VA. ...New York... As the line of showers and weak thunderstorms continues eastward along the front, occasional damaging gusts remain possible owing to mixing of stronger mid-level flow downward this afternoon. Some heating, but marginal surface moisture should keep buoyancy and the resulting updrafts weak. With MLCAPE generally less than 500 J/kg, showers and storms should steadily weaken with the loss of diurnal heating. The MRGL risk area has been trimmed behind the ongoing line. Otherwise, the prior outlook remains unchanged, see the previous discussion. ..Lyons.. 09/04/2025 .PREV DISCUSSION... /ISSUED 1124 AM CDT Thu Sep 04 2025/ ...New York into the Mid-Atlantic and Tennessee Valley... A closed mid/upper-level low will remain centered over Ontario today. Multiple mid-level perturbations will rotate around this feature through the period, including a shortwave trough forecast to advance generally east-northeastward across parts of the central Appalachians/Mid-Atlantic into the Northeast. Showers and thunderstorms are ongoing mainly ahead of a surface cold front from parts of western NY southward to the TN Valley in a low/mid-level moisture plume. Generally clear skies ahead of this activity should allow for ample daytime heating of a modestly moistened low-level airmass. Even so, 12Z observed soundings from BUF, IAD, and RNK/GSO show rather poor mid-level lapse rates, which will likely hinder updraft strength even as weak instability develops this afternoon with continued diurnal heating. Modestly enhanced southwesterly low/mid-level flow should still aid in some thunderstorm organization even with the apparent thermodynamic limitations, with multicells the dominant convective mode. Wherever low-level lapse rates can become steepened, a risk for at least isolated damaging winds remains apparent. Some hail may also occur with the strongest cores across parts of the TN Valley/southern Appalachians where locally greater instability should be present this afternoon. The Marginal Risk has been adjusted for ongoing trends, but the potential for a more focused corridor of scattered severe/damaging winds remains unclear. ...Mid Missouri Valley... A mid-level shortwave trough and attendant strong speed maximum will move quickly southeastward today from central Canada and the northern Plains towards the mid MO Valley and vicinity. Pronounced ascent associated with this jet should encourage convection to develop by late this afternoon across parts of eastern SD and vicinity. While low-level moisture and MLCAPE are both expected to remain very limited, enhanced low/mid-level northwesterly flow may still support some risk for severe gusts with any low-topped convection that can develop and spread quickly southeastward before weakening this evening with the loss of daytime heating. ...Kansas... A sharp cold front will sweep southward across the central Plains tonight. Elevated convection should form to the cool side of this boundary late tonight through early Friday morning given sufficient MUCAPE. Locally strong surface gusts and small hail may accompany this activity amid robust low-level northerlies, but the overall severe potential should remain fairly low given the tendency for convection to be mostly elevated. ...Arizona/Lower Colorado River Valley... Thunderstorms should develop again today across parts of central/southern AZ and the lower CO River Valley, beneath weak mid-level flow and on the periphery of increasing mid-level moisture associated with Tropical Storm Lorena. Weak shear should keep thunderstorms mostly disorganized, but occasional strong/gusty winds may occur where low-level lapse rates can become steepened. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Thu Sep 04 2025 Valid 042000Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF NEW YORK...TO THE MID ATLANTIC...SOUTHERN APPALACHIANS AND MID MISSOURI VALLEY... ...SUMMARY... Isolated damaging gusts remain possible across parts of New York to the Mid-Atlantic and Southern Appalachians through early this evening. Isolated severe gusts are also possible across parts of the mid Missouri Valley late this afternoon and early evening. ...20z Update Mid Atlantic and southern Appalachians... Several clusters of strong to severe thunderstorms have matured and are expected to continue through early this evening along and ahead of the slow-moving cold front from the Mid Atlantic southward. Despite poor mid-level lapse rates, heating of the modestly moist air mass is supporting around 500-1000 J/kg of MLCAPE, sufficient for a few stronger updrafts. As convection gradually increases in coverage through the remainder of this afternoon, clustering and 30-40 kt of mid-level flow will continue to support isolated damaging gust potential into early this evening. Some hail remains possible with the more cellular elements, especially father southwest over the eastern TN Valley where storm coverage should remain more isolated. The primary change was to align the western edge of the MRGL and severe probabilities with current frontal position, and shift them slightly east for ongoing storms on the border of NC and southern VA. ...New York... As the line of showers and weak thunderstorms continues eastward along the front, occasional damaging gusts remain possible owing to mixing of stronger mid-level flow downward this afternoon. Some heating, but marginal surface moisture should keep buoyancy and the resulting updrafts weak. With MLCAPE generally less than 500 J/kg, showers and storms should steadily weaken with the loss of diurnal heating. The MRGL risk area has been trimmed behind the ongoing line. Otherwise, the prior outlook remains unchanged, see the previous discussion. ..Lyons.. 09/04/2025 .PREV DISCUSSION... /ISSUED 1124 AM CDT Thu Sep 04 2025/ ...New York into the Mid-Atlantic and Tennessee Valley... A closed mid/upper-level low will remain centered over Ontario today. Multiple mid-level perturbations will rotate around this feature through the period, including a shortwave trough forecast to advance generally east-northeastward across parts of the central Appalachians/Mid-Atlantic into the Northeast. Showers and thunderstorms are ongoing mainly ahead of a surface cold front from parts of western NY southward to the TN Valley in a low/mid-level moisture plume. Generally clear skies ahead of this activity should allow for ample daytime heating of a modestly moistened low-level airmass. Even so, 12Z observed soundings from BUF, IAD, and RNK/GSO show rather poor mid-level lapse rates, which will likely hinder updraft strength even as weak instability develops this afternoon with continued diurnal heating. Modestly enhanced southwesterly low/mid-level flow should still aid in some thunderstorm organization even with the apparent thermodynamic limitations, with multicells the dominant convective mode. Wherever low-level lapse rates can become steepened, a risk for at least isolated damaging winds remains apparent. Some hail may also occur with the strongest cores across parts of the TN Valley/southern Appalachians where locally greater instability should be present this afternoon. The Marginal Risk has been adjusted for ongoing trends, but the potential for a more focused corridor of scattered severe/damaging winds remains unclear. ...Mid Missouri Valley... A mid-level shortwave trough and attendant strong speed maximum will move quickly southeastward today from central Canada and the northern Plains towards the mid MO Valley and vicinity. Pronounced ascent associated with this jet should encourage convection to develop by late this afternoon across parts of eastern SD and vicinity. While low-level moisture and MLCAPE are both expected to remain very limited, enhanced low/mid-level northwesterly flow may still support some risk for severe gusts with any low-topped convection that can develop and spread quickly southeastward before weakening this evening with the loss of daytime heating. ...Kansas... A sharp cold front will sweep southward across the central Plains tonight. Elevated convection should form to the cool side of this boundary late tonight through early Friday morning given sufficient MUCAPE. Locally strong surface gusts and small hail may accompany this activity amid robust low-level northerlies, but the overall severe potential should remain fairly low given the tendency for convection to be mostly elevated. ...Arizona/Lower Colorado River Valley... Thunderstorms should develop again today across parts of central/southern AZ and the lower CO River Valley, beneath weak mid-level flow and on the periphery of increasing mid-level moisture associated with Tropical Storm Lorena. Weak shear should keep thunderstorms mostly disorganized, but occasional strong/gusty winds may occur where low-level lapse rates can become steepened. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Thu Sep 04 2025 Valid 042000Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF NEW YORK...TO THE MID ATLANTIC...SOUTHERN APPALACHIANS AND MID MISSOURI VALLEY... ...SUMMARY... Isolated damaging gusts remain possible across parts of New York to the Mid-Atlantic and Southern Appalachians through early this evening. Isolated severe gusts are also possible across parts of the mid Missouri Valley late this afternoon and early evening. ...20z Update Mid Atlantic and southern Appalachians... Several clusters of strong to severe thunderstorms have matured and are expected to continue through early this evening along and ahead of the slow-moving cold front from the Mid Atlantic southward. Despite poor mid-level lapse rates, heating of the modestly moist air mass is supporting around 500-1000 J/kg of MLCAPE, sufficient for a few stronger updrafts. As convection gradually increases in coverage through the remainder of this afternoon, clustering and 30-40 kt of mid-level flow will continue to support isolated damaging gust potential into early this evening. Some hail remains possible with the more cellular elements, especially father southwest over the eastern TN Valley where storm coverage should remain more isolated. The primary change was to align the western edge of the MRGL and severe probabilities with current frontal position, and shift them slightly east for ongoing storms on the border of NC and southern VA. ...New York... As the line of showers and weak thunderstorms continues eastward along the front, occasional damaging gusts remain possible owing to mixing of stronger mid-level flow downward this afternoon. Some heating, but marginal surface moisture should keep buoyancy and the resulting updrafts weak. With MLCAPE generally less than 500 J/kg, showers and storms should steadily weaken with the loss of diurnal heating. The MRGL risk area has been trimmed behind the ongoing line. Otherwise, the prior outlook remains unchanged, see the previous discussion. ..Lyons.. 09/04/2025 .PREV DISCUSSION... /ISSUED 1124 AM CDT Thu Sep 04 2025/ ...New York into the Mid-Atlantic and Tennessee Valley... A closed mid/upper-level low will remain centered over Ontario today. Multiple mid-level perturbations will rotate around this feature through the period, including a shortwave trough forecast to advance generally east-northeastward across parts of the central Appalachians/Mid-Atlantic into the Northeast. Showers and thunderstorms are ongoing mainly ahead of a surface cold front from parts of western NY southward to the TN Valley in a low/mid-level moisture plume. Generally clear skies ahead of this activity should allow for ample daytime heating of a modestly moistened low-level airmass. Even so, 12Z observed soundings from BUF, IAD, and RNK/GSO show rather poor mid-level lapse rates, which will likely hinder updraft strength even as weak instability develops this afternoon with continued diurnal heating. Modestly enhanced southwesterly low/mid-level flow should still aid in some thunderstorm organization even with the apparent thermodynamic limitations, with multicells the dominant convective mode. Wherever low-level lapse rates can become steepened, a risk for at least isolated damaging winds remains apparent. Some hail may also occur with the strongest cores across parts of the TN Valley/southern Appalachians where locally greater instability should be present this afternoon. The Marginal Risk has been adjusted for ongoing trends, but the potential for a more focused corridor of scattered severe/damaging winds remains unclear. ...Mid Missouri Valley... A mid-level shortwave trough and attendant strong speed maximum will move quickly southeastward today from central Canada and the northern Plains towards the mid MO Valley and vicinity. Pronounced ascent associated with this jet should encourage convection to develop by late this afternoon across parts of eastern SD and vicinity. While low-level moisture and MLCAPE are both expected to remain very limited, enhanced low/mid-level northwesterly flow may still support some risk for severe gusts with any low-topped convection that can develop and spread quickly southeastward before weakening this evening with the loss of daytime heating. ...Kansas... A sharp cold front will sweep southward across the central Plains tonight. Elevated convection should form to the cool side of this boundary late tonight through early Friday morning given sufficient MUCAPE. Locally strong surface gusts and small hail may accompany this activity amid robust low-level northerlies, but the overall severe potential should remain fairly low given the tendency for convection to be mostly elevated. ...Arizona/Lower Colorado River Valley... Thunderstorms should develop again today across parts of central/southern AZ and the lower CO River Valley, beneath weak mid-level flow and on the periphery of increasing mid-level moisture associated with Tropical Storm Lorena. Weak shear should keep thunderstorms mostly disorganized, but occasional strong/gusty winds may occur where low-level lapse rates can become steepened. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Thu Sep 04 2025 Valid 042000Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF NEW YORK...TO THE MID ATLANTIC...SOUTHERN APPALACHIANS AND MID MISSOURI VALLEY... ...SUMMARY... Isolated damaging gusts remain possible across parts of New York to the Mid-Atlantic and Southern Appalachians through early this evening. Isolated severe gusts are also possible across parts of the mid Missouri Valley late this afternoon and early evening. ...20z Update Mid Atlantic and southern Appalachians... Several clusters of strong to severe thunderstorms have matured and are expected to continue through early this evening along and ahead of the slow-moving cold front from the Mid Atlantic southward. Despite poor mid-level lapse rates, heating of the modestly moist air mass is supporting around 500-1000 J/kg of MLCAPE, sufficient for a few stronger updrafts. As convection gradually increases in coverage through the remainder of this afternoon, clustering and 30-40 kt of mid-level flow will continue to support isolated damaging gust potential into early this evening. Some hail remains possible with the more cellular elements, especially father southwest over the eastern TN Valley where storm coverage should remain more isolated. The primary change was to align the western edge of the MRGL and severe probabilities with current frontal position, and shift them slightly east for ongoing storms on the border of NC and southern VA. ...New York... As the line of showers and weak thunderstorms continues eastward along the front, occasional damaging gusts remain possible owing to mixing of stronger mid-level flow downward this afternoon. Some heating, but marginal surface moisture should keep buoyancy and the resulting updrafts weak. With MLCAPE generally less than 500 J/kg, showers and storms should steadily weaken with the loss of diurnal heating. The MRGL risk area has been trimmed behind the ongoing line. Otherwise, the prior outlook remains unchanged, see the previous discussion. ..Lyons.. 09/04/2025 .PREV DISCUSSION... /ISSUED 1124 AM CDT Thu Sep 04 2025/ ...New York into the Mid-Atlantic and Tennessee Valley... A closed mid/upper-level low will remain centered over Ontario today. Multiple mid-level perturbations will rotate around this feature through the period, including a shortwave trough forecast to advance generally east-northeastward across parts of the central Appalachians/Mid-Atlantic into the Northeast. Showers and thunderstorms are ongoing mainly ahead of a surface cold front from parts of western NY southward to the TN Valley in a low/mid-level moisture plume. Generally clear skies ahead of this activity should allow for ample daytime heating of a modestly moistened low-level airmass. Even so, 12Z observed soundings from BUF, IAD, and RNK/GSO show rather poor mid-level lapse rates, which will likely hinder updraft strength even as weak instability develops this afternoon with continued diurnal heating. Modestly enhanced southwesterly low/mid-level flow should still aid in some thunderstorm organization even with the apparent thermodynamic limitations, with multicells the dominant convective mode. Wherever low-level lapse rates can become steepened, a risk for at least isolated damaging winds remains apparent. Some hail may also occur with the strongest cores across parts of the TN Valley/southern Appalachians where locally greater instability should be present this afternoon. The Marginal Risk has been adjusted for ongoing trends, but the potential for a more focused corridor of scattered severe/damaging winds remains unclear. ...Mid Missouri Valley... A mid-level shortwave trough and attendant strong speed maximum will move quickly southeastward today from central Canada and the northern Plains towards the mid MO Valley and vicinity. Pronounced ascent associated with this jet should encourage convection to develop by late this afternoon across parts of eastern SD and vicinity. While low-level moisture and MLCAPE are both expected to remain very limited, enhanced low/mid-level northwesterly flow may still support some risk for severe gusts with any low-topped convection that can develop and spread quickly southeastward before weakening this evening with the loss of daytime heating. ...Kansas... A sharp cold front will sweep southward across the central Plains tonight. Elevated convection should form to the cool side of this boundary late tonight through early Friday morning given sufficient MUCAPE. Locally strong surface gusts and small hail may accompany this activity amid robust low-level northerlies, but the overall severe potential should remain fairly low given the tendency for convection to be mostly elevated. ...Arizona/Lower Colorado River Valley... Thunderstorms should develop again today across parts of central/southern AZ and the lower CO River Valley, beneath weak mid-level flow and on the periphery of increasing mid-level moisture associated with Tropical Storm Lorena. Weak shear should keep thunderstorms mostly disorganized, but occasional strong/gusty winds may occur where low-level lapse rates can become steepened. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Thu Sep 04 2025 Valid 042000Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF NEW YORK...TO THE MID ATLANTIC...SOUTHERN APPALACHIANS AND MID MISSOURI VALLEY... ...SUMMARY... Isolated damaging gusts remain possible across parts of New York to the Mid-Atlantic and Southern Appalachians through early this evening. Isolated severe gusts are also possible across parts of the mid Missouri Valley late this afternoon and early evening. ...20z Update Mid Atlantic and southern Appalachians... Several clusters of strong to severe thunderstorms have matured and are expected to continue through early this evening along and ahead of the slow-moving cold front from the Mid Atlantic southward. Despite poor mid-level lapse rates, heating of the modestly moist air mass is supporting around 500-1000 J/kg of MLCAPE, sufficient for a few stronger updrafts. As convection gradually increases in coverage through the remainder of this afternoon, clustering and 30-40 kt of mid-level flow will continue to support isolated damaging gust potential into early this evening. Some hail remains possible with the more cellular elements, especially father southwest over the eastern TN Valley where storm coverage should remain more isolated. The primary change was to align the western edge of the MRGL and severe probabilities with current frontal position, and shift them slightly east for ongoing storms on the border of NC and southern VA. ...New York... As the line of showers and weak thunderstorms continues eastward along the front, occasional damaging gusts remain possible owing to mixing of stronger mid-level flow downward this afternoon. Some heating, but marginal surface moisture should keep buoyancy and the resulting updrafts weak. With MLCAPE generally less than 500 J/kg, showers and storms should steadily weaken with the loss of diurnal heating. The MRGL risk area has been trimmed behind the ongoing line. Otherwise, the prior outlook remains unchanged, see the previous discussion. ..Lyons.. 09/04/2025 .PREV DISCUSSION... /ISSUED 1124 AM CDT Thu Sep 04 2025/ ...New York into the Mid-Atlantic and Tennessee Valley... A closed mid/upper-level low will remain centered over Ontario today. Multiple mid-level perturbations will rotate around this feature through the period, including a shortwave trough forecast to advance generally east-northeastward across parts of the central Appalachians/Mid-Atlantic into the Northeast. Showers and thunderstorms are ongoing mainly ahead of a surface cold front from parts of western NY southward to the TN Valley in a low/mid-level moisture plume. Generally clear skies ahead of this activity should allow for ample daytime heating of a modestly moistened low-level airmass. Even so, 12Z observed soundings from BUF, IAD, and RNK/GSO show rather poor mid-level lapse rates, which will likely hinder updraft strength even as weak instability develops this afternoon with continued diurnal heating. Modestly enhanced southwesterly low/mid-level flow should still aid in some thunderstorm organization even with the apparent thermodynamic limitations, with multicells the dominant convective mode. Wherever low-level lapse rates can become steepened, a risk for at least isolated damaging winds remains apparent. Some hail may also occur with the strongest cores across parts of the TN Valley/southern Appalachians where locally greater instability should be present this afternoon. The Marginal Risk has been adjusted for ongoing trends, but the potential for a more focused corridor of scattered severe/damaging winds remains unclear. ...Mid Missouri Valley... A mid-level shortwave trough and attendant strong speed maximum will move quickly southeastward today from central Canada and the northern Plains towards the mid MO Valley and vicinity. Pronounced ascent associated with this jet should encourage convection to develop by late this afternoon across parts of eastern SD and vicinity. While low-level moisture and MLCAPE are both expected to remain very limited, enhanced low/mid-level northwesterly flow may still support some risk for severe gusts with any low-topped convection that can develop and spread quickly southeastward before weakening this evening with the loss of daytime heating. ...Kansas... A sharp cold front will sweep southward across the central Plains tonight. Elevated convection should form to the cool side of this boundary late tonight through early Friday morning given sufficient MUCAPE. Locally strong surface gusts and small hail may accompany this activity amid robust low-level northerlies, but the overall severe potential should remain fairly low given the tendency for convection to be mostly elevated. ...Arizona/Lower Colorado River Valley... Thunderstorms should develop again today across parts of central/southern AZ and the lower CO River Valley, beneath weak mid-level flow and on the periphery of increasing mid-level moisture associated with Tropical Storm Lorena. Weak shear should keep thunderstorms mostly disorganized, but occasional strong/gusty winds may occur where low-level lapse rates can become steepened. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0259 PM CDT Thu Sep 04 2025 Valid 042000Z - 051200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF NEW YORK...TO THE MID ATLANTIC...SOUTHERN APPALACHIANS AND MID MISSOURI VALLEY... ...SUMMARY... Isolated damaging gusts remain possible across parts of New York to the Mid-Atlantic and Southern Appalachians through early this evening. Isolated severe gusts are also possible across parts of the mid Missouri Valley late this afternoon and early evening. ...20z Update Mid Atlantic and southern Appalachians... Several clusters of strong to severe thunderstorms have matured and are expected to continue through early this evening along and ahead of the slow-moving cold front from the Mid Atlantic southward. Despite poor mid-level lapse rates, heating of the modestly moist air mass is supporting around 500-1000 J/kg of MLCAPE, sufficient for a few stronger updrafts. As convection gradually increases in coverage through the remainder of this afternoon, clustering and 30-40 kt of mid-level flow will continue to support isolated damaging gust potential into early this evening. Some hail remains possible with the more cellular elements, especially father southwest over the eastern TN Valley where storm coverage should remain more isolated. The primary change was to align the western edge of the MRGL and severe probabilities with current frontal position, and shift them slightly east for ongoing storms on the border of NC and southern VA. ...New York... As the line of showers and weak thunderstorms continues eastward along the front, occasional damaging gusts remain possible owing to mixing of stronger mid-level flow downward this afternoon. Some heating, but marginal surface moisture should keep buoyancy and the resulting updrafts weak. With MLCAPE generally less than 500 J/kg, showers and storms should steadily weaken with the loss of diurnal heating. The MRGL risk area has been trimmed behind the ongoing line. Otherwise, the prior outlook remains unchanged, see the previous discussion. ..Lyons.. 09/04/2025 .PREV DISCUSSION... /ISSUED 1124 AM CDT Thu Sep 04 2025/ ...New York into the Mid-Atlantic and Tennessee Valley... A closed mid/upper-level low will remain centered over Ontario today. Multiple mid-level perturbations will rotate around this feature through the period, including a shortwave trough forecast to advance generally east-northeastward across parts of the central Appalachians/Mid-Atlantic into the Northeast. Showers and thunderstorms are ongoing mainly ahead of a surface cold front from parts of western NY southward to the TN Valley in a low/mid-level moisture plume. Generally clear skies ahead of this activity should allow for ample daytime heating of a modestly moistened low-level airmass. Even so, 12Z observed soundings from BUF, IAD, and RNK/GSO show rather poor mid-level lapse rates, which will likely hinder updraft strength even as weak instability develops this afternoon with continued diurnal heating. Modestly enhanced southwesterly low/mid-level flow should still aid in some thunderstorm organization even with the apparent thermodynamic limitations, with multicells the dominant convective mode. Wherever low-level lapse rates can become steepened, a risk for at least isolated damaging winds remains apparent. Some hail may also occur with the strongest cores across parts of the TN Valley/southern Appalachians where locally greater instability should be present this afternoon. The Marginal Risk has been adjusted for ongoing trends, but the potential for a more focused corridor of scattered severe/damaging winds remains unclear. ...Mid Missouri Valley... A mid-level shortwave trough and attendant strong speed maximum will move quickly southeastward today from central Canada and the northern Plains towards the mid MO Valley and vicinity. Pronounced ascent associated with this jet should encourage convection to develop by late this afternoon across parts of eastern SD and vicinity. While low-level moisture and MLCAPE are both expected to remain very limited, enhanced low/mid-level northwesterly flow may still support some risk for severe gusts with any low-topped convection that can develop and spread quickly southeastward before weakening this evening with the loss of daytime heating. ...Kansas... A sharp cold front will sweep southward across the central Plains tonight. Elevated convection should form to the cool side of this boundary late tonight through early Friday morning given sufficient MUCAPE. Locally strong surface gusts and small hail may accompany this activity amid robust low-level northerlies, but the overall severe potential should remain fairly low given the tendency for convection to be mostly elevated. ...Arizona/Lower Colorado River Valley... Thunderstorms should develop again today across parts of central/southern AZ and the lower CO River Valley, beneath weak mid-level flow and on the periphery of increasing mid-level moisture associated with Tropical Storm Lorena. Weak shear should keep thunderstorms mostly disorganized, but occasional strong/gusty winds may occur where low-level lapse rates can become steepened. Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook NWS Storm Prediction Center Norman OK 0229 PM CDT Thu Sep 04 2025 Valid 061200Z - 071200Z ...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM THE MID-ATLANTIC INTO THE NORTHEAST... ...SUMMARY... Widely scattered thunderstorms will pose a risk of damaging wind gusts across parts of the Mid-Atlantic into the Northeast on Saturday. ...Synopsis... A broad/amplified mid/upper-level trough encompassing much of the eastern CONUS will shift slightly eastward through the forecast period, while an accompanying strong upper-level jet advances northeastward across Quebec. In the low-levels, a related north-south-oriented cold front will move eastward across the Northeast and Mid-Atlantic region through the afternoon. ...Northeast into the Mid-Atlantic... Ahead of the eastward-moving cold front, diurnal heating/ destabilization of a moist boundary layer (middle/upper 60s to lower 70s dewpoints) will contribute to a corridor of moderate surface-based buoyancy (1000-2000 J/kg MLCAPE) from the Mid-Atlantic into the Northeast -- despite poor midlevel lapse rates. Diurnal heating and related buoyancy may be limited with northward extent owing to increased cloud coverage near the right-entrance region of the upper-level jet. As the front intercepts the destabilizing/uncapped pre-convective air mass, widely scattered thunderstorms should develop along/immediately ahead of the front during the afternoon. Around 35-45 kt of front-parallel effective shear will support a mix of loosely organized convective bands and clusters. Given the enhanced deep-layer unidirectional flow and steepening low-level lapse rates, damaging wind gusts will be possible with the stronger storms into the evening. Depending on the degree of destabilization over parts of the Mid-Atlantic into the Northeast, an eventual upgrade may be warranted. ..Weinman.. 09/04/2025 Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0208 PM CDT Thu Sep 04 2025 Valid 051200Z - 061200Z A rather expansive IsoDryT area was added as scattered to widespread mixed wet/dry thunderstorms are expected across central Oregon/vicinity tomorrow with more isolated coverage into western Oregon and western/central Washington. Late evening and nocturnal thunderstorms are possible in portions of central/eastern/northwest Oregon and western Washington. While wetting rain is likely in portions of central/eastern Oregon, the amount of lightning and dry to very dry fuels as evident by new ignitions and active to extreme fire behavior on large fires in the region support the introduction of an IsoDryT area. Storms will track generally northward at 10-20 knots likely producing abundant lightning, including outside of the cores, with drier air moving into portions of southern/central Oregon behind them. Precipitable water values will range from 0.7-1.3" in the IsoDryT area and training of storms with some of those higher PWAT values will lead to wetting rain in areas. The onshore flow/marine layer is also precluding including more of coastal Oregon in the IsoDryT area as it looks to deepen tomorrow, but thunderstorms may go up the Coast Ranges late tomorrow. Deep pyroconvection remains possible on very active large wildfires in the Northwest, north Idaho, and California. A complicating factor in this forecast is the quantity of smoke that will be in the region from existing fires and being transported southward from Canada. ..Nauslar.. 09/04/2025 .PREV DISCUSSION... /ISSUED 1249 AM CDT Thu Sep 04 2025/ ...Synopsis... A secondary mid-level wave will traverse the Pacific Northwest on D2/Friday. This wave will bring much cooler temperatures, higher relative humidity, and potential for more widespread thunderstorm activity. While lightning efficiency may increase, increase coverage of thunderstorms and better organization with increasing shear should promote heavier cores and wetting rainfall potential. As such, no isolated thunderstorm areas were included at this time. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0208 PM CDT Thu Sep 04 2025 Valid 051200Z - 061200Z A rather expansive IsoDryT area was added as scattered to widespread mixed wet/dry thunderstorms are expected across central Oregon/vicinity tomorrow with more isolated coverage into western Oregon and western/central Washington. Late evening and nocturnal thunderstorms are possible in portions of central/eastern/northwest Oregon and western Washington. While wetting rain is likely in portions of central/eastern Oregon, the amount of lightning and dry to very dry fuels as evident by new ignitions and active to extreme fire behavior on large fires in the region support the introduction of an IsoDryT area. Storms will track generally northward at 10-20 knots likely producing abundant lightning, including outside of the cores, with drier air moving into portions of southern/central Oregon behind them. Precipitable water values will range from 0.7-1.3" in the IsoDryT area and training of storms with some of those higher PWAT values will lead to wetting rain in areas. The onshore flow/marine layer is also precluding including more of coastal Oregon in the IsoDryT area as it looks to deepen tomorrow, but thunderstorms may go up the Coast Ranges late tomorrow. Deep pyroconvection remains possible on very active large wildfires in the Northwest, north Idaho, and California. A complicating factor in this forecast is the quantity of smoke that will be in the region from existing fires and being transported southward from Canada. ..Nauslar.. 09/04/2025 .PREV DISCUSSION... /ISSUED 1249 AM CDT Thu Sep 04 2025/ ...Synopsis... A secondary mid-level wave will traverse the Pacific Northwest on D2/Friday. This wave will bring much cooler temperatures, higher relative humidity, and potential for more widespread thunderstorm activity. While lightning efficiency may increase, increase coverage of thunderstorms and better organization with increasing shear should promote heavier cores and wetting rainfall potential. As such, no isolated thunderstorm areas were included at this time. ...Please see www.spc.noaa.gov/fire for graphic product... Read more