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SPC Aug 24, 2023 2000 UTC Day 1 Convective Outlook
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0255 PM CDT Thu Aug 24 2023 Valid 242000Z - 251200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN LOWER MICHIGAN INTO WESTERN PENNSYLVANIA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER NORTH DAKOTA...AND FROM LAKE MICHIGAN TO CENTRAL PENNSYLVANIA AND WESTERN NEW YORK... ...SUMMARY... A swath of severe thunderstorms appears increasingly likely to occur across parts of southern Lower Michigan through northern Ohio and northwest Pennsylvania this evening. Damaging winds with localized significant severe wind gusts in excess of 75 mph along with a few tornadoes should be the primary hazards. ...Great Lakes Region... Little change was needed for the 20Z update. A very unstable air mass will continue to develop northeastward across Lower MI, Lake Erie and southwest Ontario through this evening, as heights begin to fall ahead of a developing shortwave trough to the northwest. A leading disturbance will likely aid storm formation close to Lake MI later this afternoon. This activity is likely to grow upscale during the evening and into the night as it moves southeastward out of Lower MI. Damaging winds will be likely given the extreme instability and expected MCS mode. Swaths of significant gusts are possible given the steep midlevel lapse rates and substantial precipitable water aiding updraft/downdraft potential. A few of the stronger storms may additionally produce large hail, especially the early development from southeast WI into western Lower MI later this afternoon. For more information see MCD 2037. ...Northern Plains... Scattered severe cells producing hail appear likely this afternoon from ND into northwest MN as a cold front interacts with a destabilizing air mass and an upper trough grazes the region. Hail potential will be aided by substantial hodograph length with effective shear around 50 kt, along with steep lapse rates. See MCD 2036 for more information. ..Jewell.. 08/24/2023 .PREV DISCUSSION... /ISSUED 1130 AM CDT Thu Aug 24 2023/ ...Central to Lower Great Lakes and Upper OH Valley... In the wake of decaying elevated convection earlier this morning, substantially decreasing cloudiness is well underway across most of OH into southern Lower MI. A very moist boundary layer persists to the west of an arcing convective outflow bisecting IN that will largely mix out and advect east this afternoon. This increasing moisture coupled with rather steep mid-level lapse rates sampled in the 12Z DTX/GRB soundings, in conjunction with the surface heating recovery will yield a plume of very large MLCAPE spreading into southern Lower MI. This will result in a substantial MLCAPE gradient from south to north across the lower peninsula, with a more west to east gradient farther east downstream of the Lower Great Lakes. A low-amplitude mid-level disturbance and related speed max over eastern ON into Upper MI should progress into southeast ON, with trailing belt of weakly forced ascent aiding in a minor frontal wave over south-central WI tracking towards southwest Lower MI by early evening. The west-east corridor ahead of this wave across southern Lake MI, southern/central Lower Michigan toward the Lake Erie vicinity is where deep convection is most likely to initiate towards 00Z. Intense storm development can be expected including some initial supercells capable of large hail and possibly a tornado threat, which could somewhat focus across southeast Lower MI near the warm front/surface wave. Storms should quickly increase and organize through the evening toward the Lake Erie vicinity including northern OH/western PA, with damaging wind potential becoming more prevalent. Given the very large instability, some threat for localized gusts in excess of 75 mph will exist as an MCS matures, with the possibility of a QLCS-related tornado risk also persisting. The severe wind threat should continue through the evening into and across parts of the upper Ohio Valley and central Appalachians before convection eventually weakens. Confidence is adequate to warrant an upgrade of damaging wind probabilities for a level 3 of 5 severe risk. ...ND and northwest MN... A shortwave trough over southwest SK should track east-southeast into southeast MB through tonight. Ascent associated with this trough along with modest low-level convergence along a weak front, should encourage convection to develop late this afternoon across parts of ND. Weak to moderate buoyancy and strong deep-layer shear will support organized updrafts with a few supercells and multicell clusters expected. Scattered large hail and isolated severe wind gusts should be the main threat with these thunderstorms as they move eastward into parts of northwest MN through this evening. Confidence is adequate to warrant an upgrade of the large hail probabilities for a level 2 of 5 severe risk. ...Western SD/NE... At least isolated high-based convection should form towards late afternoon near the Black Hills and along a lee trough. While deep-layer shear should be weaker with southward extent across this area relative to ND, it may still be sufficient for loosely organized multicells posing an isolated severe wind and marginal severe hail threat through the early evening. ...Central/Southern Appalachians... A pair of remnant MCVs and related convective outflows from early-day convection should spread south within a modest mid-level northerly flow regime. Ahead of these features, continued boundary-layer heating within the west/east-oriented MLCAPE gradient should support some threat for loosely organized multicells capable of producing sporadic strong to damaging wind gusts. Read more
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0255 PM CDT Thu Aug 24 2023 Valid 242000Z - 251200Z ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM SOUTHERN LOWER MICHIGAN INTO WESTERN PENNSYLVANIA... ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER NORTH DAKOTA...AND FROM LAKE MICHIGAN TO CENTRAL PENNSYLVANIA AND WESTERN NEW YORK... ...SUMMARY... A swath of severe thunderstorms appears increasingly likely to occur across parts of southern Lower Michigan through northern Ohio and northwest Pennsylvania this evening. Damaging winds with localized significant severe wind gusts in excess of 75 mph along with a few tornadoes should be the primary hazards. ...Great Lakes Region... Little change was needed for the 20Z update. A very unstable air mass will continue to develop northeastward across Lower MI, Lake Erie and southwest Ontario through this evening, as heights begin to fall ahead of a developing shortwave trough to the northwest. A leading disturbance will likely aid storm formation close to Lake MI later this afternoon. This activity is likely to grow upscale during the evening and into the night as it moves southeastward out of Lower MI. Damaging winds will be likely given the extreme instability and expected MCS mode. Swaths of significant gusts are possible given the steep midlevel lapse rates and substantial precipitable water aiding updraft/downdraft potential. A few of the stronger storms may additionally produce large hail, especially the early development from southeast WI into western Lower MI later this afternoon. For more information see MCD 2037. ...Northern Plains... Scattered severe cells producing hail appear likely this afternoon from ND into northwest MN as a cold front interacts with a destabilizing air mass and an upper trough grazes the region. Hail potential will be aided by substantial hodograph length with effective shear around 50 kt, along with steep lapse rates. See MCD 2036 for more information. ..Jewell.. 08/24/2023 .PREV DISCUSSION... /ISSUED 1130 AM CDT Thu Aug 24 2023/ ...Central to Lower Great Lakes and Upper OH Valley... In the wake of decaying elevated convection earlier this morning, substantially decreasing cloudiness is well underway across most of OH into southern Lower MI. A very moist boundary layer persists to the west of an arcing convective outflow bisecting IN that will largely mix out and advect east this afternoon. This increasing moisture coupled with rather steep mid-level lapse rates sampled in the 12Z DTX/GRB soundings, in conjunction with the surface heating recovery will yield a plume of very large MLCAPE spreading into southern Lower MI. This will result in a substantial MLCAPE gradient from south to north across the lower peninsula, with a more west to east gradient farther east downstream of the Lower Great Lakes. A low-amplitude mid-level disturbance and related speed max over eastern ON into Upper MI should progress into southeast ON, with trailing belt of weakly forced ascent aiding in a minor frontal wave over south-central WI tracking towards southwest Lower MI by early evening. The west-east corridor ahead of this wave across southern Lake MI, southern/central Lower Michigan toward the Lake Erie vicinity is where deep convection is most likely to initiate towards 00Z. Intense storm development can be expected including some initial supercells capable of large hail and possibly a tornado threat, which could somewhat focus across southeast Lower MI near the warm front/surface wave. Storms should quickly increase and organize through the evening toward the Lake Erie vicinity including northern OH/western PA, with damaging wind potential becoming more prevalent. Given the very large instability, some threat for localized gusts in excess of 75 mph will exist as an MCS matures, with the possibility of a QLCS-related tornado risk also persisting. The severe wind threat should continue through the evening into and across parts of the upper Ohio Valley and central Appalachians before convection eventually weakens. Confidence is adequate to warrant an upgrade of damaging wind probabilities for a level 3 of 5 severe risk. ...ND and northwest MN... A shortwave trough over southwest SK should track east-southeast into southeast MB through tonight. Ascent associated with this trough along with modest low-level convergence along a weak front, should encourage convection to develop late this afternoon across parts of ND. Weak to moderate buoyancy and strong deep-layer shear will support organized updrafts with a few supercells and multicell clusters expected. Scattered large hail and isolated severe wind gusts should be the main threat with these thunderstorms as they move eastward into parts of northwest MN through this evening. Confidence is adequate to warrant an upgrade of the large hail probabilities for a level 2 of 5 severe risk. ...Western SD/NE... At least isolated high-based convection should form towards late afternoon near the Black Hills and along a lee trough. While deep-layer shear should be weaker with southward extent across this area relative to ND, it may still be sufficient for loosely organized multicells posing an isolated severe wind and marginal severe hail threat through the early evening. ...Central/Southern Appalachians... A pair of remnant MCVs and related convective outflows from early-day convection should spread south within a modest mid-level northerly flow regime. Ahead of these features, continued boundary-layer heating within the west/east-oriented MLCAPE gradient should support some threat for loosely organized multicells capable of producing sporadic strong to damaging wind gusts. Read more
