Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Apr 05 2023 12:57:10 ACUS01 KWNS 051257 SWODY1 SPC AC 051255 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0755 AM CDT Wed Apr 05 2023 Valid 051300Z - 061200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF THE MID-SOUTH TO THE UPPER GREAT LAKES... ....SUMMARY... Severe thunderstorm winds, large hail and a few tornadoes are expected today from the Great Lakes to parts of east Texas and Louisiana. ....Synopsis... The dominant upper-air feature for this period will remain a trough over the Rockies and Plains States, though its influence will wane with time as the feature deamplifies. An associated/embedded low -- now apparent in moisture-channel imagery over eastern ND -- is expected to move northeastward across northwestern MN to far western parts of northwestern ON by 00Z. A positively tilted, synoptic- scale trough will extend from there southwestward across the central Plains to southern CO. By 12Z, the mid/upper cyclone will pull off to the northeast over the James Bay region, with weakening trough southwestward across WI/IA to the central Plains. As the mid/upper cyclone ejects and the trailing trough weakens, the flow to its south and southwest will remain strong and southwesterly, but become flatter/less-cyclonic, with neutral to weak isallohypsic fields from about the Ohio Valley southward and minor height falls farther north. The 11Z surface analysis showed the main/occluded cyclone -- associated with its counterpart aloft -- just north of MSP. A triple point was located down the occluded front over southwestern WI, with warm front initially drawn approximately eastward over southern Lower MI and northeastern OH. An arctic cold front extended from that triple point over central MO, southeastern OK, and north-central/northwest TX. The warm front should move northeastward across Lower MI and the Lower Great Lakes through the day, overtaken by the occluded front from northwest-southeast. The cold front should merge with/overtake a Pacific front initially drawn across portions of northeast/north-central TX southwestward to between DRT-LRD. By 00Z, the combined cold front should extend from southeastern Lower MI across southern IN, western KY, southern AR, northwestern LA, and portions of the middle TX Coast, to the lower Rio Grande Valley of deep south TX. By 12Z, the cold front should reach eastern NY, central PA, WV, southwestward over northwestern AL and central LA to the middle TX coast, where it will stall. ....Great Lakes to east TX/LA... An extensive and complex severe scenario is underway with a large corridor of severe-thunderstorm potential -- ongoing this morning from northeast TX to the Upper Great Lakes. This threat will spread eastward into a destabilizing air mass across the outlook area today, offering all severe hazards (tornado, large-hail and damaging-gust threats). The main severe concern will be with a quasi-linear convective system (QLCS) currently evident along/ahead of the arctic front and mainly along/just behind the Pacific front. These two regimes may merge over the next several hours as the fronts will, and result in a more coherent, lengthy, single QLCS belt. At least isolated severe will be possible with warm-sector convection ahead of the QLCS, strongly dependent on mode (wind with the clustered activity, all hazards from any warm-sector supercells, hail with supercells north of the warm front). Please see SPC watches numbered 121-125 and related mesoscale discussions for near-term coverage of the severe threats in their respective areas. Broadly favorable low-level theta-e will exist in the outlook corridor, with stronger deep-layer winds and large-scale support in northern areas -- closer to the ejecting mid/upper trough. Southwesterly, 50-70-kt effective-shear vectors should be common across the outlook area, while hodograph size and SRH maximize along the warm front and gradually diminish southwestward from there. Deep-shear and mean-wind vectors will be aligned only slightly to the right of the cold front, suggesting associated convection should maintain warm-sector inflow, but remain largely linear. Meanwhile, moisture will decrease northward but still be favorable, with surface dewpoints commonly in the upper 60s F from the lower Ohio Valley southwestward, and low/mid 60s from there to the warm front. The main convective band should weaken this evening into tonight over the middle/upper Ohio Valley into central NY, as it both outruns the most-favorable low-level theta-e advection and encounters a nocturnally stabilizing boundary layer. Farther south, large-scale forcing for ascent will be more displaced from the near-frontal lift with time, though steeper low/middle- level lapse rates and at least adequate shear still will support some storm organization and severe wind/hail potential. Development of thunderstorms atop the front this evening and tonight is possible, with isolated severe (mainly hail) relatively early in convective evolution, before training convection renders unsuitably clustered/messy mode. ...Edwards/Weinman.. 04/05/2023 $$ = = = 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) .