Severe Storms

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Mon Jun 23 2025 Valid 241200Z - 251200Z ...Southern Great Basin/Four Corners region... Stronger mid-level flow ahead of an upper-level trough will remain over the greater Four Corners region. Efficient daytime boundary later mixing will continue to promote a corridor of breezy southwest winds amid afternoon relative humidity of 10-15 percent to promote Elevated fire weather conditions from northern Arizona, southeastern Arizona into southern Wyoming. ...Northern Nevada... Some convection aided by higher terrain is expected across northern Nevada Tuesday afternoon. Limited instability/moisture profiles along with marginal fuel dryness (ERC values in the 80-85 percentile range) should limit ignition efficiency of slow moving isolated showers and thunderstorms across the area. ..Williams.. 06/23/2025 .PREV DISCUSSION... /ISSUED 0111 AM CDT Mon Jun 23 2025/ ...Synopsis... Another day of elevated fire weather conditions is expected for parts of the intermountain West on Tuesday. An upper trough currently settling into the southern Great Basin/lower CO River Valley is expected to stall and slowly de-amplify over the next 48 hours. This will maintain a belt of modest mid-level flow over parts of the eastern Great Basin/western Four Corners region. Although pressure gradient winds will generally be in the mid/upper teens, diurnal heating and deep mixing of a dry air mass will promote frequent gusts between 20-35 mph across the region - especially from northern AZ into eastern UT and southern WY under a belt of somewhat stronger 700-500 mb flow. Afternoon RH minimums in the low to mid teens are expected, and coupled with dry fuels, will help support another day of elevated fire weather conditions (though transient periods of critical conditions are anticipated where stronger gusts can occur). ...Dry Thunderstorms... Isolated thunderstorms appear possible Tuesday afternoon across portions of northeastern Nevada under the upper-level low. Cold temperatures aloft combined with modest mid-level moisture and strong low-level heating will support thermodynamic profiles adequate for weak convection, but perhaps limited precipitation. Given dry fuels across the region, some dry-thunderstorm risk is expected. The primary limiting factor to a more substantial dry-thunderstorm concern is slow storm motions (less than 10 knots), which should increase the probability of wetting rainfall under the convective cores. ...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 0258 PM CDT Mon Jun 23 2025 Valid 241200Z - 251200Z ...Southern Great Basin/Four Corners region... Stronger mid-level flow ahead of an upper-level trough will remain over the greater Four Corners region. Efficient daytime boundary later mixing will continue to promote a corridor of breezy southwest winds amid afternoon relative humidity of 10-15 percent to promote Elevated fire weather conditions from northern Arizona, southeastern Arizona into southern Wyoming. ...Northern Nevada... Some convection aided by higher terrain is expected across northern Nevada Tuesday afternoon. Limited instability/moisture profiles along with marginal fuel dryness (ERC values in the 80-85 percentile range) should limit ignition efficiency of slow moving isolated showers and thunderstorms across the area. ..Williams.. 06/23/2025 .PREV DISCUSSION... /ISSUED 0111 AM CDT Mon Jun 23 2025/ ...Synopsis... Another day of elevated fire weather conditions is expected for parts of the intermountain West on Tuesday. An upper trough currently settling into the southern Great Basin/lower CO River Valley is expected to stall and slowly de-amplify over the next 48 hours. This will maintain a belt of modest mid-level flow over parts of the eastern Great Basin/western Four Corners region. Although pressure gradient winds will generally be in the mid/upper teens, diurnal heating and deep mixing of a dry air mass will promote frequent gusts between 20-35 mph across the region - especially from northern AZ into eastern UT and southern WY under a belt of somewhat stronger 700-500 mb flow. Afternoon RH minimums in the low to mid teens are expected, and coupled with dry fuels, will help support another day of elevated fire weather conditions (though transient periods of critical conditions are anticipated where stronger gusts can occur). ...Dry Thunderstorms... Isolated thunderstorms appear possible Tuesday afternoon across portions of northeastern Nevada under the upper-level low. Cold temperatures aloft combined with modest mid-level moisture and strong low-level heating will support thermodynamic profiles adequate for weak convection, but perhaps limited precipitation. Given dry fuels across the region, some dry-thunderstorm risk is expected. The primary limiting factor to a more substantial dry-thunderstorm concern is slow storm motions (less than 10 knots), which should increase the probability of wetting rainfall under the convective cores. ...Please see www.spc.noaa.gov/fire for graphic product... Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more

SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0254 PM CDT Mon Jun 23 2025 Valid 232000Z - 241200Z ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES... ...SUMMARY... Storms with occasional damaging outflow gusts and marginally severe hail will be possible today from the southern and central Plains northeastward into the Great Lakes. ...20z Update... Marginal hail and tornado probabilities were introduced across western Maine with this update. CAM guidance suggests supercells moving out of southern Quebec may track into western Maine. The moist and unstable environment across this region would be supportive of hail, wind, and perhaps a tornado as 850 mb flow increases through the evening. Otherwise, the forecast remains on track with no updates needed. See previous discussion for more information. ..Thornton.. 06/23/2025 .PREV DISCUSSION... /ISSUED 1122 AM CDT Mon Jun 23 2025/ ...Upper Great Lakes to the Plains this afternoon/evening... A surface cold front will make slow southeastward progress from WI to IA and KS, in the wake of a primary shortwave trough moving over western ON. Surface heating is ongoing ahead of the front, where boundary-layer dewpoints range from the upper 60s to lower 70s beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of 2000-3000 J/kg. Convective inhibition will likewise weaken by early-mid afternoon, when thunderstorm development is likely along the front and differential heating zone in the SLGT risk corridor. Deep-layer flow will be a little stronger toward WI in closer proximity to the main belt of westerlies, where a mix clusters/line segments and transient supercell structures will be possible. The primary severe threat will be damaging outflow winds (60-70 mph) from roughly 20z-03z, though isolated large hail of 1-1.5 inches in diameter may also occur with the strongest storms. More loosely organized storm clusters are expected this afternoon through this evening into the southern High Plains, where thermodynamic profiles will favor isolated severe downbursts. ...Northern Maine later this evening... Around the northern periphery of a closed midlevel high over the Appalachians, a series of embedded speed maxima will move over ON/QC through tonight. Boundary-layer dewpoints in the 60s beneath midlevel lapse rates near 7 C/km, in combination with daytime heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective inhibition by late afternoon. Thunderstorm development is expected upstream across QC in association with an embedded speed max/surface wave, and this convection will approach northern ME by late evening/early tonight. Though buoyancy will slowly weaken with the loss of daytime heating, low-level hodograph curvature and deep-layer westerly shear should be sufficient for an organized storm cluster to reach ME before weakening overnight. Isolated damaging winds will be the main threat with these storms. Read more