Subj : DAY1SVR: Day 1 Convective To : All From : Mike Powell Date : Wed Sep 27 2023 09:51:00 ACUS01 KWNS 271234 SWODY1 SPC AC 271233 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0733 AM CDT Wed Sep 27 2023 Valid 271300Z - 281200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS AFTERNOON INTO TONIGHT ACROSS PARTS OF SOUTHERN ILLINOIS...SOUTHERN INDIANA...WESTERN AND NORTH CENTRAL KENTUCKY... ....SUMMARY... Scattered strong thunderstorms may impact parts of the lower Ohio Valley today into tonight, and pose some risk for severe weather. ....Synopsis... A vigorous mid-level short wave trough progressing inland of the Pacific Northwest coast is forecast to continue an east-northeastward progression today through tonight, across the northern U.S. Rockies into the Saskatchewan/Montana border vicinity by 12Z Thursday. As this occurs, downstream blocking mid-level ridging, initially centered along an axis south of Hudson Bay into the St. Lawrence Valley vicinity, may undergo more notable suppression by tonight, and a modest mid-level low to its southwest may slowly accelerate eastward across southwestern portions of the Great Lakes region. In lower-levels, sprawling surface ridging, centered over Quebec, will maintain considerable influence across the U.S., from the Atlantic Seaboard into the Great Plains. However, broad weak surface troughing will continue to be supported beneath the southern periphery of the mid-level low, across the lower Missouri into Ohio Valleys. Within this troughing, westward into the surface troughing to the lee of the Front Range, one notable baroclinic zone will be maintained. A weaker front likely will linger across northern Florida and adjacent south Atlantic and Gulf coastal areas, with high precipitable water content generally confined to areas along and to its south, beneath broad troughing within a weak southern branch of westerlies. ....Lower Ohio Valley vicinity... Although generally south of the modest cold core (around or below -14 C at 500 mb) of the slow moving mid-level low, it appears that a gradual moistening of the boundary-layer may contribute to destabilization with heating, along and south of the quasi-stationary baroclinic zone. CAPE increasing to 1000-1500+ J/kg probably will initially be focused south through east of the remnants of a cluster of storms now spreading across southern Illinois into the lower Ohio Valley. While models suggest that this convection will dissipate this morning, forcing for ascent associated with a supporting mid-level jet streak (including 30-40 kt in the 700-500 mb layer) may contribute to renewed thunderstorm development across the east central Kentucky Bluegrass into Cumberland Plateau vicinity by mid afternoon. A couple of stronger cells may be accompanied by small to marginally severe hail and localized potentially damaging wind gusts, before the associated forcing for ascent spreads into a more stable environment and/or weakens. In the wake of the initial perturbation, more substantive boundary-layer destabilization (including CAPE increasing in excess of 1000 J/kg) may commence along the baroclinic zone, east-southeast of St. Louis through the Louisville vicinity from mid to late afternoon into this evening. Preceding another mid-level jet streak propagating east-southeastward out of the lower Missouri Valley, and perhaps coinciding with a zone of strengthening low-level warm advection to the east of a developing weak frontal wave, it is possible that the environment may become conducive to the evolution of a few supercell structures and/or a small organized thunderstorm cluster. ...Kerr/Bentley.. 09/27/2023 $$ --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .