Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Aug 17 2023 12:48:12 ACUS01 KWNS 171248 SWODY1 SPC AC 171246 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0746 AM CDT Thu Aug 17 2023 Valid 171300Z - 181200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE CENTRAL/SOUTHERN GREAT LAKES AND MID-ATLANTIC REGIONS... ....SUMMARY... Isolated strong to severe thunderstorms are possible across parts of the central/southern Great Lakes region today, and perhaps parts of the Mid-Atlantic region this evening and tonight. ....Synopsis... As a strong mid/upper-level shortwave trough digs southeastward from the Gulf of Alaska toward southwestern BC, a currently cut-off 500-mb low well offshore from central CA will pivot east- southeastward toward the coast (but remain offshore through 12Z tomorrow). As that occurs, the main mid/upper-level anticyclone -- now loosely organized and elongated from the interior Northwest to west TX -- will consolidate around a high over southern CO or northern NM. By 12Z, that high should shift southeastward to the TX Panhandle, with large-amplitude synoptic ridging moving eastward across the northern Plains. That ridge will build as a downstream cyclone and trough strengthen further. Moisture-channel imagery indicates a well-developed mid/upper cyclone centered over northwestern ON, with trough southwestward across IA. The low should move southeastward to near Georgian Bay by the end of the period, with a more neutrally tilted trough southward over WV and the Carolinas. The 11Z surface analysis showed the associated cold front across central parts of Lake Superior and the MI U.P., southwestward over southern WI, southeastern IA, central KS, and central/southeastern CO. This front should sweep across the Great Lakes and Ohio Valley through the period, reaching central/eastern NY, northern/western VA, middle TN, and the TX/OK Red River region by 12Z. ....Central/southern Great Lakes States... An ongoing, prefrontal line of elevated thunderstorms is evident across portions of northern/western Lower MI and adjoining Lake Michigan, becoming more broken to isolated in storm coverage southwestward across northern/western IL. This activity may pose a threat for isolated severe hail in the near term, while still atop a strongly stabilized boundary layer from prior/overnight cooling. With time today, either this activity, and/or frontal convection in corridor of destabilization behind it, will encounter more surface- based effective-inflow parcels, and increasing potential for damaging to severe gusts as well. However, the translational speed of the trough aloft, cold front and prefrontal convective forcing all appear to outpace optimally favorable theta-e advection across the warm-sector. The foregoing boundary layer will remain in a state of only partial recovery following the passage of a former cold front now stalled across the Gulf Coast region. A plume of low/mid 60s F surface dewpoints, limited diabatic heating between areas of thicker cloud cover, and the southeastern rim of increasing large-scale lift aloft, should contribute to the development of a narrow area of 500-1000 J/kg MLCAPE. Elevated MUCAPE of 1000-1500 J/kg will cover somewhat greater area to the east and north, thanks to strong moist/warm advection above the surface. Effective-shear magnitudes of 45-55 kt will favor organized convection, though lack of greater moisture/instability cast doubt on attaining severe potential normally expected with such a seemingly favorable mid/upper pattern. ....Mid-Atlantic region... Isolated to scattered thunderstorms are possible by late afternoon along a prefrontal surface trough in central PA, with isolated convection in the less-focused warm sector farther east toward the coast. While this activity may produce strong gusts, organization is not expected to peak until later in the evening. By then, large-scale ascent and deep-layer winds, as well as low-level moisture through mass-response-driven advective processes, all will increase ahead of the progressive/intense mid/upper-level trough. The still-prefrontal primary convective plume should move more quickly eastward across the outlook area, into a lower- elevation, destabilizing low-level environment characterized by dewpoints increasing into the mid 60s to low 70s F. These factors should weaken an antecedently strong stable layer near 600 mb enough to yield minimally inhibited MLCAPE of around 1000-1500 J/kg in northern areas, and 1500-2500 J/kg near Chesapeake Bay and the Delmarva Peninsula. The increasingly organized convection may yield strong/damaging and isolated severe gusts, and a conditional tornado threat may develop with a marginally favorable increase in boundary- layer hodograph size. ...Edwards/Jewell.. 08/17/2023 $$ = = = 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) .