Subj : DAY1SVR: Day 1 Convective Outlook To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Sep 26 2023 05:07:47 ACUS01 KWNS 260507 SWODY1 SPC AC 260506 Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1206 AM CDT Tue Sep 26 2023 Valid 261200Z - 271200Z ....THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS THE MIDWEST AND FROM CENTRAL NEW MEXICO TO SOUTHWEST TEXAS... ....SUMMARY... Thunderstorms capable of producing isolated hail and strong wind gusts will be possible this afternoon and tonight across parts of Illinois and Indiana, and also across parts of New Mexico into west Texas. ....Synopsis... Latest water-vapor imagery depicts an amplified upper ridge shifting east from the Intermountain West into the Plains over the past 12 hours. An occluded low over the upper MS River Valley is beginning to shift to the southeast within the mean northwesterly flow regime, and is expected to reside across central IL by peak heating. Filtered heating of a moist airmass currently in place across the Midwest, combined with weak ascent in the vicinity of the low, will support scattered thunderstorm development this afternoon and evening. To the south, a weak surface high over OK is fostering modest moisture return flow into NM. Thunderstorm development is expected by mid to late afternoon within the upslope flow regime, and may feature a few strong/severe storms. ....Midwest... Thunderstorms will likely be ongoing across northern IL and adjacent areas of IA and WI at the start of the period to the east of the surface low within a weak warm advection regime. A second round of thunderstorms is probable along the surface trough during the afternoon hours across IL as ascent associated with the left-exit region of a weak upper jet overspreads a weakly capped environment. Cold temperatures aloft should support SBCAPE values on the order of 500-1000 J/kg, but values up to 1500 J/kg are possible depending on the degree of daytime heating and residual cloud cover. Regardless, deep-layer shear is forecast to be adequate (around 20-25 knots) to support a few stronger cells capable of large hail and damaging gusts. A brief/weak tornado is possible with initial cells along the surface trough and in the vicinity of the surface low where forecast soundings show some low-level veering and effective SRH values on the order of 100-150 m2/s2. ....New Mexico and Southwest Texas... 04 UTC surface observations show a plume of 50-60 F dewpoints advecting to the west/northwest into southeast NM. With no appreciable strengthening of the surface high expected over the next 12 hours, further moistening into the 50s and low 60s across much of southern NM appears probable by mid-afternoon with MLCAPE values around 1500-2000 J/kg. Temperatures climbing into the 80s and low 90s should mix through the nocturnal inversion, allowing for convective initiation within the upslope flow regime around peak heating. Despite fairly weak northwesterly flow aloft, southeasterly low-level winds will support straight hodographs with sufficient effective bulk shear (around 30 knots) for organized cells with an attendant large hail and severe wind risk. ...Moore/Leitman.. 09/26/2023 $$ = = = 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) .