Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Mar 24 2023 20:02:33 ACUS01 KWNS 242002 SWODY1 SPC AC 242000 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0300 PM CDT Fri Mar 24 2023 Valid 242000Z - 251200Z ....THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF LOUISIANA...ARKANSAS...MISSISSIPPI...AND FAR SOUTHWEST TENNESSEE... ....SUMMARY... A severe weather outbreak remains possible across the Lower Mississippi Valley and Mid-South this afternoon and tonight, with isolated large hail, scattered damaging/severe winds, and several tornadoes expected. The most likely time period for strong tornadoes is between 5 pm and Midnight CDT. ....20Z Update... No changes have been made to the Moderate Risk area. Convection is beginning to increase in coverage and intensity ahead of the cold across far east TX, in addition to the ongoing activity along the front itself. As a southerly low-level jet strengthens late this afternoon into this evening, a corresponding increase in effective SRH will likely lead to greater tornado potential with time. The greatest threat for strong tornadoes remains apparent this evening across parts of northern LA into southern/eastern AR, northern/central MS, and western/middle TN. This will especially be the case with any supercells that can remain discrete ahead of the line. A bowing line/MCS will likely develop this evening as convection grows upscale along/ahead of the front. The northern extent of appreciable severe threat will likely be constrained by a convectively reinforced outflow boundary from thunderstorms earlier today that currently extends from parts of AR into TN. This boundary will attempt to lift back northward this evening and overnight as a surface low deepens from the Mid-South into the lower OH Valley. Still, the threat for damaging winds and tornadoes should become increasingly limited with northward extent into KY and the OH Valley. The primary change with this update was to expand severe wind probabilities and corresponding categorical lines a bit eastward across AL/TN, north GA, and western NC/SC. Recent high-resolution guidance, including multiple runs of the HRRR, suggest that a well-organized bow will continue eastward across these areas late tonight into early Saturday morning. Although instability is forecast to remain weak, very strong low-level shear associated with a 55-65+ kt low-level jet should allow the line to remain organized and pose a continued threat for severe/damaging winds and a few embedded QLCS tornadoes. ...Gleason.. 03/24/2023 ..PREV DISCUSSION... /ISSUED 1126 AM CDT Fri Mar 24 2023/ ....Lower Mississippi Valley/Mid-South/Tennessee Valley... Upper-air analysis and more contemporary water vapor imagery features a relatively low amplitude shortwave trough centered near the New Mexico/Mexico/west Texas border vicinity, with a preceding broad belt of strong mid/high-level southwesterlies extending across the southern plains toward the Midwest. These westerlies are partially atop a convectively augmented front that extends from central/northeast Texas into the Ozarks, and then largely parallels the Lower Ohio River (but to the south). Within the warm sector, 12z upper-air analysis did feature a relative minimum of higher-caliber source-region moisture as noted in 850mb analysis (supplemented by GPS PW values) across parts of south-central/east Texas into southern Louisiana, although higher moisture content was noted across the ArkLaTex/Mid-South. Scattered thunderstorms are ongoing along the effective frontal zone from the ArkLatex into central/eastern Arkansas, and northeastward into western Tennessee and eastern Kentucky. Latest thinking is that initial development/intensification of surface-based storms should occur across northeast/east Texas, possibly far southeast Oklahoma, into western Arkansas in vicinity of the front/abating outflow and surface low vicinity. This severe threat should expand/organize east-northeastward as the surface cyclone steadily deepens and tracks northeast along the baroclinic zone through tonight. After some initial-discrete storms/supercells, it seems like that an intensifying QLCS will evolve across Arkansas and spread toward the Tennessee Valley through the evening. Strengthening low-level winds and enlarging hodographs should compensate for the northern gradient of the surface-based instability plume. This QLCS will likely contain embedded supercell and mesovortex structures supportive of tornadoes (including potential for a few EF2s) and significant damaging wind swaths (up to around 80-90 mph). Farther south, increasing low-level moisture across the Sabine Valley towards the ArkLaMiss should eventually yield a plume of moderate MLCAPE around 1500 J/kg by evening. This warm theta-e advection regime should also foster some discrete supercellular convection ahead and south/southeast of the QLCS towards late afternoon into early evening within the resultant MLCAPE gradient. Deep-layer shear profiles will support supercells, a few of which could become long-tracked across the ArkLaMiss region. Low-level hodographs, while not quite as enlarged as compared to farther north, will support a threat for strong tornadoes (EF2+) through much of the evening, until warm sector winds becomes increasingly veered from southwest to northeast overnight. $$ = = = To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. 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