Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Feb 15 2023 12:59:47 ACUS01 KWNS 151259 SWODY1 SPC AC 151258 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0658 AM CST Wed Feb 15 2023 Valid 151300Z - 161200Z ....THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE MID-SOUTH REGION... ....SUMMARY... Severe thunderstorms with large to very large hail are possible over parts of north Texas and southern Oklahoma this afternoon and evening. A threat for tornadoes, severe-thunderstorm winds and isolated hail will also develop overnight over the lower Mississippi Valley/Mid-South region. ....Synopsis... Following the departure of a formerly closed mid/upper perturbation (now over the Upper Great Lakes), the main feature of interest is a synoptic-scale cyclone now over much of the Great Basin and Desert Southwest. The associated 500-mb low -- centered initially near the eastern part of the AZ/UT line -- is forecast to pivot eastward across the Four Corners this morning and southern Rockies through the day, then to near CAO by 00Z. During the ensuing 12 hours, the low should move northeastward to near MHK, with trough southwestward across the northern TX Panhandle to central portions of NM and AZ. The 11Z surface analysis showed a quasistationary to warm front, left behind the previous mid/upper-level system, from the lower Ohio Valley southwestward across central AR and east to south-central TX. A separate, quasistationary front was drawn from southern MO across eastern/southwestern OK, then west-northwestward to a low over northwestern NM. The residual/southern front should become diffuse as it shifts northward and northwestward through the day, amidst a broad low-level warm/moist advection regime, with its western part backing into a dryline this afternoon. In the 21-00Z time frame, the dryline should extend from near the south-central OK low across north-central TX just west of the Metroplex, southward to near LRD. In the northern frontal zone, a wave low should develop over south-central OK by around 00Z, deepening as it ripples northeastward along the boundary overnight. By 12Z, the low should reach southeastern MO, with cold front south-southwestward over central AR, northwestern LA, southeast TX, and the middle/lower TX Coastal Plain. ....Early phase: north TX/southern OK... A few strong-severe thunderstorms are possible late this afternoon into evening on either side of the Red River, from about I-35 eastward, with all severe hazards possible. This includes large to very large hail with any mature supercell(s), and a slight tornado threat. Buoyancy will increase throughout the day amidst diurnal insolation/ heating and moist advection, with 60s F surface dewpoints nearing the dryline by late afternoon. Low and high clouds may limit heating somewhat for parts of the day, but each should break up enough to permit peak surface temps well into the 70s F (and perhaps near 80) east of the dryline -- considerably warmer than shown in NAM forecast soundings, and somewhat warmer than most other progs. Accordingly modified RAP hourly soundings for the DAL-ADM corridor yield up to 1500-2000 J/kg MLCAPE, with minimal MLCINH by late afternoon for initiation near the developing surface low (where boundary-layer convergence is maximized) and adjoining dryline segment. Convection should move into veering wind profiles with height that yield enlarged low-level hodographs. Effective SRH around 150-200 J/kg before 00Z should increase to 250-300 J/kg in the evening under a strengthening LLJ over southeastern OK and north-central/northeast TX. The same modified soundings also match several historic analogs for significant hail (at least 2 inches diameter) and tornadoes. With time later this evening and overnight, this eastward-shifting convective process may become messier and more linear, as frontal forcing increases, parallel to mid/upper winds. Though this would decrease the hail sizes, damaging gusts and a tornado threat still will be possible. ....Late phase: Arklatex/east TX, to TN Valley/Mid-South... A complex convective scenario is apparent across this region, mainly overnight with tornadoes, severe gusts and isolated large hail all possible. A couple tornadoes may be strong (EF2+ damage capable). A conditional threat for supercells exists this afternoon into early evening over parts of southern/central LA and east TX, as heating gradually deepens the boundary layer and weakens MLCINH within an environment of increasing ambient shear. However, lift will be modest overall, and relatively maximized on ascent axes of horizontal convective rolls, indicating a gradual-development scenario with uncertainties on convective coverage and storm- maturation latency. Scattered thunderstorms should develop this evening into tonight in a roughly west-east corridor across parts of AR, northern MS, and western/middle TN, near the northeastward-shifting leading edge of the relatively rich moisture in the return-flow plume, where surface-based effective-inflow parcels begin. A few embedded supercells are possible, offering all severe hazards. Additionally, a strengthening, southwest/northeast-aligned, low-level confluence/ convergence zone is forecast tonight across parts of the Mid-South, also initiating strong-severe convection (including a few supercells). This convection may develop/merge upscale into a quasi-linear arrangement, with its western part potentially overtaken by activity moving out of the eastern OK/AR/Arklatex regions. Substantial low-level moisture is already in place from the southern parts of this corridor to the Gulf Coast and beyond, east of the residual front. This is manifest as surface dewpoints commonly in the mid-60s now, from around I-20 in LA/MS southward; such moisture will spread northward/inland throughout the day and evening. By evening, low LCL, surface-based parcels, and effective SRH of 200- 400 J/kg will favor growing severe potential. ...Edwards/Smith.. 02/15/2023 $$ = = = 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) .