Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Nov 20 2023 06:02:38 ACUS01 KWNS 200602 SWODY1 SPC AC 200600 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1200 AM CST Mon Nov 20 2023 Valid 201200Z - 211200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF FAR EAST TEXAS...CENTRAL LOUISIANA AND SOUTHWEST MISSISSIPPI... ....SUMMARY... Severe thunderstorms are likely this afternoon into tonight from east Texas, into parts of the Lower-Mississippi Valley, and Southeast States. Damaging winds and several tornadoes, a few of which may be strong, will be the primary hazards. Though damaging winds and some large hail are also possible. ....Synopsis... A broad positively tilted mid-level trough and jet streak over the southern Rockies is forecast to consolidate and strengthen rapidly into an upper low moving over the Southern Plains and the lower Mississippi Valley by late tonight. Several more neutral to negatively tilted shortwave perturbations embedded within the 80-90 kt jet streak will round the base of the trough and eject over the ArkLaTex and Southeast ahead of the main trough this afternoon. Broad diffluence and strong forcing for ascent will aid a surface low over OK as it moves northeastward toward the Mississippi River tonight. Strong low-level mass response ahead of the trough and the surface low should draw a warm front with rich low-level moisture (dewpoints in the 60s F) as far north as the MS/TN border. While mid-level lapse rates are modest, strong differential thermal advection and ascent should allow for the development of weak to moderate buoyancy sufficient for scattered severe storms over parts of the ArklaTex and Southeast states this afternoon into tonight. ....East TX into the lower Mississippi Valley... A complex convective evolution is expected today with widespread showers and thunderstorms likely to be ongoing north and east of the surface warm front across eastern OK, AR and parts of northeast TX at the start of the period. Isentropic ascent should remain strong through the morning hours with weak showers and broken to overcast skies likely throughout the warm sector. While this will likely inhibit surface heating to some degree, a few cloud breaks and low-level warm advection along a pre-frontal confluence axis in east TX should allow for weak to moderate destabilization and scattered storm development by mid morning to early afternoon. Veered surface flow with relatively weak shear and high RH in the low-levels suggests a messy storm evolution with early updrafts. However, strong line-normal mid and upper-level shear components should allow for the gradual intensification of individual supercell structures within a broader cluster or broken line ahead of the surface cold front across east-central TX. Albeit gradual, owing to modest low and mid-level lapse rates, the maturation of these storms through the mid to later afternoon will eventually overlap with a strongly sheared-low-level air mass as the main upper jet ejects over parts of far east TX, southern AR, and LA. 0-500m SRH of 100-150 m2/s2 and STP values of 2-3 will likely support strong low-level mesocyclones with the potential for tornadoes, some of which could be strong. These storms should continue eastward through the evening hours with a risk for tornadoes before gradual upscale growth into a loose QLCS increases the potential for damaging winds over central and eastern MS into western AL. Across parts of eastern AR into western/central TN and northern MS/AL, low-level destabilization appears much less favorable with multiple rounds of warm advection precipitation ahead of the surface low and main trough. A few model solutions bring the warm front far enough north to generate some positive near-surface buoyancy immediately ahead of the cold front. A fine-line QLCS may evolve with a low-end risk for damaging wind gusts given mixing of the strong background wind field to the surface. ....Southern AL and Gulf Coast tonight... As the warm front lifts north over parts of southeastern LA and southern MS this afternoon and evening, rich Gulf moisture will move quickly inland beneath a 30-40 kt low-level jet. While it is uncertain if storms can develop given modest forcing, a few supercells may evolve within the warm sector and track northeastward toward the strongly sheared frontal zone. A few tornadoes could develop in the evening hours ahead of the main band of convection farther west. Later tonight, the storms ahead of the cold front should gradually coalesce into a QLCS as the front shifts eastward. With strong low-level wind fields and at least some buoyancy remaining in place, damaging gusts and isolated tornadoes are possible well into the overnight hours across southeastern MS, southwest AL and possibly the western FL Panhandle. However, confidence in the eastward extent of the severe risk will depend greatly on the onshore destabilization which, given the diurnal timing, is not a guarantee. ...Lyons/Darrow.. 11/20/2023 $$ = = = 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) .