Subj : HVYRAIN: Excessive Rainfall Discussion To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Apr 22 2023 08:21:06 FOUS30 KWBC 220821 QPFERD Excessive Rainfall Discussion NWS Weather Prediction Center College Park MD 420 AM EDT Sat Apr 22 2023 Day 1 Valid 12Z Sat Apr 22 2023 - 12Z Sun Apr 23 2023 ....THERE IS A SLIGHT RISK FOR EXCESSIVE RAINFALL FOR A PORTION OF CENTRAL TEXAS... ....Central Texas... The rainfall forecast across central Texas has increased markedly this forecast cycle. The pattern remains similar, but the guidance is locking in on the potential for training thunderstorms. At the surface, southeasterly flow will increase through the day today across south Texas, turning more southerly as it advances east of the dryline across central Texas. At the northern end of this plume of moisture, a cold front will be advancing southward, drawing unseasonably cold air southward across the Plains. The collision point between these two air masses is likely to be over central Texas. A bit higher up in the atmosphere, the warm, moist air will advance much further north into northern Texas. The separation between surface and mid-level fronts opens up the possibility for separate areas of training convection to develop. Most of the guidance suggest the surface/southern front will feature stronger storms than the northern one over north central Texas. Nonetheless either or or both may act as foci for convection. Steering flow/Corfidi vectors all across Texas will be westerly at about 15 kts, which means any storms that form will move off to the east. However, the persistent southeasterly flow of Gulf moisture colliding with the front will support backbuilding storms along the front. There is good agreement that this training pattern will develop, but much less agreement on where. Thus, the inherited Marginal Risk area was expanded well to the north to cover the area where storms may develop along the mid-level front over north central Texas. Those storms that form south of the Red River may track into the Dallas-Fort Worth metro. However, the greater threat and better agreement will be along the surface front further south closer to San Antonio/Austin. The most likely area of development will be north of San Antonio and west of Austin. This area happens to be the same one that was hard hit just 24 hours ago with strong, slow-moving, training thunderstorms, which produced numerous instances of flash flooding. This area has not yet fully recovered. Thus, FFGs in this particular area are lower than they would be at any other time. The better agreement in the CAMs of this area being the focus for training thunderstorms, and coordination with the EWX/San Antonio, TX and SJT/San Angelo, TX forecast offices necessitated a local upgrade to a Slight Risk, covering the area that has both lower FFGs and much greater forecasted rainfall. This remains a low confidence forecast, and as such, changes with future updates are more likely than usual for a Day 1 forecast. ....Mid-Atlantic... A single squall line is forecast to move east across all of the Mid-Atlantic later today. The progressive nature of the storms, high FFGs, and very dry antecedent conditions are keeping this area's flash flood threat below Marginal Risk thresholds. Wegman Day 2 The Day 2 outlook will be updated by 0830Z. Day 3 The Day 3 outlook will be updated by 0830Z. Day 1 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/94epoints.txt__;!!DZ3fjg!4fl2Uh2MiLYfUGgEAuUgotEf5S-rQXzVHac6XD54Avsr= VMtRqJb7ZFhzJZhr1ddumqSQ8vIlFVcO9ZHjKrj7GQ725qI$=20 Day 2 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/98epoints.txt__;!!DZ3fjg!4fl2Uh2MiLYfUGgEAuUgotEf5S-rQXzVHac6XD54Avsr= VMtRqJb7ZFhzJZhr1ddumqSQ8vIlFVcO9ZHjKrj7Szodm10$=20 Day 3 threat area: https://urldefense.com/v3/__https://www.wpc.ncep.noaa.go= v/qpf/99epoints.txt__;!!DZ3fjg!4fl2Uh2MiLYfUGgEAuUgotEf5S-rQXzVHac6XD54Avsr= VMtRqJb7ZFhzJZhr1ddumqSQ8vIlFVcO9ZHjKrj7i5GtfbM$=20 $$ =3D =3D =3D 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) .