Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Feb 27 2024 13:00:09 ACUS01 KWNS 271300 SWODY1 SPC AC 271258 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0658 AM CST Tue Feb 27 2024 Valid 271300Z - 281200Z ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE MIDWEST VICINITY... ....SUMMARY... Scattered strong to severe thunderstorms, associated with large hail (some 2 inches diameter), damaging gusts, and a few tornadoes will be possible from late this afternoon into the evening and overnight, from parts of the mid Mississippi Valley to the Ohio Valley and southern Great Lakes. ....Synopsis... A progressive upper trough over the western U.S. this morning is forecast to advance steadily eastward into/across the Plains this afternoon and evening, and then onward toward the Mid and Upper Mississippi Valley overnight. In tandem with the advance of this feature, a strengthening surface cold front currently stretching from the Upper Mississippi Valley to northeastern Colorado will continue plunging southeastward across the Plains through the day. A somewhat ill-defined frontal low will gradually consolidate into this evening over the northern Illinois vicinity, moving northeastward across Lower Michigan overnight. As it does, the trailing cold front will continue to surge southward/southeastward into/across the Midwest/Mid Mississippi Valley/Southern Plains overnight. By 12Z Wednesday, the front should extend from Lake Huron, south across the Middle Ohio Valley, and then southwestward across the Tennessee valley to the Texas Coastal Plain. ....The Midwest vicinity... Ahead of the advancing cold front, southerly low-level flow will continue to advect low-level moisture northward, beneath a low-level inversion/cap evident in morning RAOBs from the southern Plains into the Midwest. Evolution of this gradually moistening but capped low-level airmass will likely be a key determinant with respect to degree of convective evolution -- and the intensity thereof -- late this afternoon/and this evening. Low-level airmass concerns aside, the evolving scenario otherwise remains favorable for severe potential across the Midwest and vicinity. Steep lapse rates are evident above the low-level inversion, and increasingly strong deep-layer flow will accompany the advance of the upper system, and gradual consolidation of the surface frontal low. As such, from a broad dynamic and kinematic perspective, the pattern continues to appear favorable. Thermodynamically, there remain concerns that the boundary layer will remain somewhat cool/stable, relative to the warmer air in the roughly 900 to 800 mb layer. Further, heating/mixing will also result in mixing out, to some degree, of the shallow surface-based moisture returning northward on low-level southerly flow within the developing warm sector. With all that said, 500 to 1000 J/kg mixed-layer CAPE should characterize the boundary layer by late afternoon/early evening, as the front approaches. This will result in isolated to scattered storm development -- initially over the northern Illinois vicinity but later farther south nearer the Ohio Valley -- possibly in a somewhat bimodal manner with a relative minimum in between. Eventually, through mid to late evening, increasingly widespread storms should be expanding across the Midwest/Ohio Valley region, which will then continue eastward across the Upper Ohio Valley and toward the central Appalachians through the end of the period. Given the favorable kinematic environment, at least isolated organized/rotating storms are expected, with some upscale growth into bands possibly occurring overnight and spreading eastward with time. Along with potential for large hail -- locally near 2" in diameter, locally strong/damaging wind gusts are also expect with stronger storms/storm clusters. Additionally, a few tornadoes may also occur, though uncertainties regarding low-level moisture/instability suggest overall tornado potential should remain limited. ...Goss/Broyles.. 02/27/2024 $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .