Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat May 20 2023 12:38:23 ACUS01 KWNS 201238 SWODY1 SPC AC 201236 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0736 AM CDT Sat May 20 2023 Valid 201300Z - 211200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON/EVENING ACROSS MS/AL AND VICINITY...SOUTHWEST NM AND VICINITY...CENTRAL OR/WA...AND THE LOWER RIO GRANDE VALLEY OF TX... ....SUMMARY... Strong to isolated severe thunderstorms are possible this afternoon/evening across parts of the Southeast, southern New Mexico region, central Oregon and Washington, and the lower Rio Grande Valley in Texas. ....MS/AL area this afternoon/evening... A midlevel shortwave trough over the mid MS Valley will rotate east-southeastward over the TN Valley by this evening, and will be preceded by a diffuse/remnant MCV now over the MS/TN border. An associated surface cold front will likewise move southeastward into central/southern LA/MS/AL by tonight. Boundary-layer dewpoints in the 65-70 F range will spread northeastward from MS into AL in advance of the cold front, while surface heating contributes to destabilization by this afternoon (MLCAPE near 1500 J/kg). This will support scattered thunderstorms along and ahead of the front by early-mid afternoon and continuing into the evening. Deep-layer speed shear/hodograph length will favor some storm-scale organization, including low-end supercell potential. However, low-level flow/shear will be weak, along with poor midlevel lapse rates. Thus, while isolated wind damage and marginally severe hail may occur, the overall severe threat is expected to remain marginal. ....Southwest NM and vicinity this afternoon/evening... A weak midlevel low persists over Sonora, while low-level moisture is advecting westward across southern NM in association with a surface cold front. Surface heating and the modest increase in low-level moisture from the east will support scattered thunderstorms this afternoon from the higher terrain in southeast AZ eastward into southwest NM. MLCAPE of 500-1000 J/kg, steep low-level lapse rates, and modest deep-layer vertical shear (low-level easterlies below mid-upper level south-southwesterlies) will support a few cells/clusters capable of producing strong outflow gusts of 50-60 mph and marginally severe hail. ....Central OR/WA this afternoon/evening... Convection is again expected near and east of the Cascade crest, and storms will spread north-northeastward through late afternoon/evening. Boundary-layer dewpoints in the upper 40s to mid 50s, surface heating, and midlevel lapse rates of 7.5-8 C/km will support MLCAPE near 1000 J/kg, in an environment with effective bulk shear of 30-35 kt. Isolated damaging gusts and large hail will be the main threats for a few hours late this afternoon/evening. ....Lower Rio Grande Valley today... Overnight convection is weakening near the middle TX coast, a little ahead of a surface cold front moving slowly southeastward across south central/southeast TX. Boundary-layer dewpoints in the 68-72 F range are present across south TX, beneath remnant midlevel lapse rates near 7.5 C/km per 12z soundings. There are some concerns about persistent clouds given the recent storm development in the upslope flow across extreme northeast Mexico, and how much surface heating will be limited. All told, confidence is low in any particular details of the convective evolution today, and the severe threat is expected to remain marginal at best. ...Thompson/Broyles.. 05/20/2023 $$ = = = 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) .