Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat May 06 2023 12:55:02 ACUS01 KWNS 061254 SWODY1 SPC AC 061253 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0753 AM CDT Sat May 06 2023 Valid 061300Z - 071200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS BIG COUNTRY/NORTH-CENTRAL TX INTO FAR SOUTHERN OK... ....THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS MID-MS VALLEY... ....SUMMARY... Intense severe thunderstorm development is likely during the late afternoon and evening across a portion of the southern Great Plains. Very large hail and destructive wind events are possible across the Big Country and North-Central Texas into southern Oklahoma. Lower confidence potential exists for intense severe thunderstorms including a few tornadoes across parts of the Mid-Mississippi Valley States this evening into tonight. ....Southern Great Plains... In the wake of convection yesterday, the remnants of which consist of a small MCS over south LA this morning, a pervasive dry pocket remains across much of north TX. Rich Gulf moisture has been relegated to south Texas into the Edwards Plateau and Concho Valley, but will be advected back north through the day. This was well sampled by the 12Z DRT sounding with a mean-mixing ratio near 16 g/kg beneath very steep mid-level lapse rates around 9 C/km. The dryline is expected to mix to the western Edwards Plateau north to the Big Country and then northeast into central OK in the late afternoon. Convective development is likely in this time frame over the Big Country as surface temperatures once again heat well through the 90s along and west of the dryline amid nearly full insolation. A few additional storms should also develop farther southeast into central TX along the edge of the rich Gulf moisture. Moist sector buoyancy will be quite large owing to the very steep lapse rates with MLCAPE reaching 3000-4000 J/kg. Deep-layer shear however, will be more muted with 500-mb southwesterlies only around 25-30 kt. Given the very strong instability, outflow-dominated splitting supercells are expected with more discrete updrafts being capable of producing very large hail. A modest increase in low-level southerlies during the evening should support further upscale growth with probable eastward propagation of an MCS into north-central TX. Significant severe wind gusts from damaging downbursts will be possible, most likely in the latter supercell to peak MCS stage as increasing MLCIN and modest deep-layer shear/weak large-scale forcing for ascent suggest an overall weakening trend should occur overnight. Consensus of CAM soundings also suggest that the severe wind threat will extend farther north across at least southern OK, even within the stratiform to anvil region of the MCS during the evening. ....Mid-MS Valley Vicinity... Below-average confidence exists in the most likely evolution of convective potential today through tonight. But conditionally, a reasonable worst-case scenario could consist of significant severe across all three hazards, with a best-case scenario of a lower-end severe hail/wind threat. Have expanded the cat 2/SLGT risk by upgrading coverage/intensity probabilities to indicate the area with greater relative severe potential this evening into tonight. Remnants of a recently decayed MCS are ongoing in central IA with elevated convection increasing within the buoyancy gradient across northern MO. It is plausible that this increase will persist into midday as the surface warm front advances northeast towards the Lower MO Valley. Isolated severe hail would be the main threat in this time frame. The surface cyclone just east of RSL should drift east-northeast towards the STJ vicinity by late afternoon, as a pair of minor shortwave impulses (one over SD and the other over WY) effectively consolidate over the eastern Dakotas to MN by tonight. Upper 80s to mid 90s surface temperatures should be common to the southwest of the cyclone in the post-dryline airmass over eastern to southern KS with a pronounced surface warm front across MO. Guidance varies markedly with the environment ahead of the cyclone from cool/moist profiles that are capped to surface-based development to warm/well-mixed profiles and more volatile warm/moist profiles with minimal inhibition. This environmental uncertainty also manifests with substantial spread across guidance in convective evolution during the evening through tonight. Conditionally, a favorable corridor for sustained supercell development is plausible just ahead of the cyclone and near the warm front during the early evening along the IA/MO border area. This scenario is most supported by the 09Z RAP environment and 00Z ECMWF and WRF-ARW convective signals. If supercells can become established and anchor along the warm front or surface trough farther north in IA...ample buoyancy, rather steep mid-level lapse rates, and an enlarged low-level hodograph would support a significant severe threat. The 09Z HRRR environment contrasts with its parent RAP depicting greater MLCIN near the warm front and failing to sustain early evening convection south of I-80. Strengthening low-level warm theta-e advection after sunset will support increasing convective development tonight. Farther north activity will be elevated, but storms closer to the warm front should be able to ingest surface-based inflow despite near-neutral lowest 1 km lapse rates. More northern scenarios suggest a slightly-elevated MCS may evolve across east-central IA east along the IL/WI border area with more southern scenarios taking a track centered on northeast MO into central IL. A mixed threat of at least isolated large hail and damaging winds will be possible into the overnight period as the plume of large buoyancy in the undisturbed airmass over MO advects northeast. ....Southeast LA vicinity... An MCS is ongoing over south-central LA with an MCV crossing the MS River. Locally strong gusts have been measured during the past hour and with MLCAPE near 2000 J/kg in the 12Z LIX sounding, this may persist despite the tendency for diurnal decay. See MCD 687 for further information. Renewed convective development may occur during the afternoon, but 00Z CAM guidance poorly simulated this MCS where as the 09Z HRRR/RRFS has some semblance of it. They suggest convection should tend to form on the backside of the remnant MCV, despite the overturning in its wake. Should this occur, modest deep-layer flow may be augmented by the remnant MCV to support isolated damaging winds and severe hail with the stronger storms. ...Grams/Kerr.. 05/06/2023 $$ = = = 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) .