Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Sep 12 2023 19:53:48 ACUS01 KWNS 121953 SWODY1 SPC AC 121952 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 0252 PM CDT Tue Sep 12 2023 Valid 122000Z - 131200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF THE EAST AND SOUTHWEST... ....SUMMARY... Isolated severe thunderstorms remain possible this afternoon into tonight, across parts of the southern Appalachians to Mid-Atlantic States, south Georgia to central Florida, and southern Arizona to southwest New Mexico. ....20Z Update... Some minor adjustments have been made to the general thunderstorm lines, but no changes have been made to the severe probabilities. See the previous discussion below for more information, and MCD 2140 regarding the short-term threat for northeast GA into parts of the Carolinas and southern VA. ...Dean.. 09/12/2023 ..PREV DISCUSSION... /ISSUED 1129 AM CDT Tue Sep 12 2023/ ....Appalachians/Mid-Atlantic States... Broad height falls will occur regionally in advance of the upper trough centered near the Great Lakes/northern Ontario. Moderate differential diabatic heating will occur today ahead of a weak southwest/northeast-oriented baroclinic zone. This will aid the development of scattered thunderstorms through early/mid afternoon from the Tennessee Valley to the central Appalachians. Poor mid-level lapse rates will limit overall buoyancy and updraft vigor, but at least weak buoyancy coupled with 25-35 kt effective bulk shear should support multicell clusters and an attendant threat for sporadic damaging winds this afternoon through early evening. While a spatial decrease in the severe threat is expected after sunset, some uptick in severe risk may occur tonight as greater mid-level height falls overspread richer low-level moisture over the Chesapeake and Delmarva regions. With weak surface low development expected, low-level mass response and low-level shear/SRH may be adequate for a few transient supercells. These supercells should generally remain weak, but could potentially pose a low-probability brief tornado threat aside from localized wind damage. ....Florida/southern Georgia... A minor mid-level trough over the north-central Gulf will slowly progress east and remain well offshore through the period. Downstream of this feature, 500-mb west-southwesterly winds of 15-25 kt will persist and support short-duration/transient storm organization. As surface temperatures warm into the upper 80s to low 90s, isolated to scattered thunderstorms will develop along the sea breezes and collide inland. Ample buoyancy with MLCAPE of 2000-2500 J/kg will support vigorous downdrafts and sporadic wind gusts from 45-65 mph, along with the possibility of marginally severe hail from 0.75 to 1.25 inches. ....Southern Arizona/southwest New Mexico... A belt of confluent mid-level westerlies will yield a swath of 30-35 kt flow across the region, supporting potential for isolated severe thunderstorms from late afternoon through tonight. Mid-level lapse rates will be modest and timing/extent of large-scale ascent appears nebulous with multiple rounds of thunderstorm development from this morning through tonight. Although somewhat tempered by lingering early day clouds and precipitation, a plume of weak to moderate buoyancy should become established this afternoon south of the Mogollon Rim, with the strongest regional destabilization across parts of southwest into south-central Arizona. Scattered thunderstorms seem most likely during the late afternoon and evening within the buoyancy gradient and across the higher terrain. Sporadic occurrences of 50-60 mph wind gusts along with marginally severe hail around 1 inch will be possible through the period. $$ = = = 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) .