Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Dec 30 2022 12:58:40 ACUS01 KWNS 301258 SWODY1 SPC AC 301257 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0657 AM CST Fri Dec 30 2022 Valid 301300Z - 311200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS NEAR THE CENTRAL GULF COAST... ....SUMMARY... Isolated damaging gusts and a brief tornado or two are possible into this afternoon near the central Gulf Coast. ....Synopsis... In mid/upper levels, a high-amplitude, progressive synoptic trough is apparent from the northern High Plains southward to the central/ southern High Plains and over northern and central MX. A series of shortwave troughs will move through the associated cyclonic flow at various latitudes, keeping the greater trough progressive such that it reaches the eastern Dakotas, eastern parts of NE/KS/OK, and northeast TX to Coahuila by the end of the period. A leading shortwave trough -- evident in moisture-channel imagery over eastern OK, the Arklatex region and the Sabine Valley region, will eject northeastward across parts of the Mid-South, Ozarks and lower Ohio Valley through the period. Upstream, another perturbation was apparent over central/southern NM and northern Chihuahua. This feature should amplify by 00Z as it moves through the synoptic trough over west-central TX and Coahuila, then pivot east-northeastward to LA by 12Z. At the surface, 11Z analysis depicted a cold front from eastern Lake Superior across northern IL, southeastern MO, northern AR, and east TX, where prior convective processes and postconvective pressure falls have diffused the front temporarily. The front was better- defined again just off the lower/middle TX Coast. The cold front will proceed eastward over the lower Ohio and mid/lower Mississippi Valleys through the period. However, the cold front will play little direct role in the severe threat, with organized convection remaining ahead of it. The synoptic warm front was drawn across the northeastern Gulf, just southwest of MOB, and near JAN, moving only slowly northward and being overtaken by convection northwest of JAN. This process will continue through the period, shunting the north vertex of a roughly triangular-shaped, partially modified, inland warm sector southward (seaward) with time. ....Central Gulf Coast... Isolated, marginally severe gusts and/or a brief tornado are possible with a band of thunderstorms forecast to move eastward across the outlook area today into this evening, before the convection outpaces the geographic extent of favorable destabilization and weakens over the lower Chattahoochee/ Apalachicola River Valley region tonight. Gust potential will be greatest in bowing segments and embedded mesocirculations, the latter also offering the marginal tornado threat. The main adjustment to the outlook area for this cycle was to trim the western rim behind the ongoing MCS. The strongest parameter space for supercells/tornadoes, by far, will be over the open Gulf south of a pool of relatively cold sea-surface temperatures (SSTs) near the coast. There, favorable low-level and deep shear will overlap return flow trajectories that have been well-modified into maritime/tropical form. Farther north, deep- tropospheric flow over inland areas will bear a substantial southerly/line-parallel component, helping to maintain quasi-linear convective structure. Still, sufficient speed shear and slight veering with height will be present in the warm sector, such that 35-45-kt effective-shear vectors will be common (locally/briefly higher). A relative local max in vertical shear by most measures will exist along the warm front as well, though buoyancy will be weakest this northeastern edge of the warm sector compared to areas nearer the coast. Due to abundant/persistent clouds and precip, the air mass inland will struggle to destabilize, especially in term of lapse rates in the lowest 1 or 2 km. Nonetheless, marginally sufficient low-level warm/moist advection and vertical mixing should occur to support surface-based effective-inflow parcels, over and past an area of very shallow, relatively stable air related to the cool SSTs. However, forecast soundings suggest that inland surface temperatures and dewpoints in the mid/upper 60s F can offset modest midlevel lapse rates enough for MLCAPE around 1000 J/kg near and south of I-10, and 200-500 J/kg MLCAPE farther inland in the shrinking warm sector. ...Edwards/Broyles.. 12/30/2022 $$ = = = 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) .