Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Mar 27 2025 18:58:42 AWUS01 KWNH 271858 FFGMPD TXZ000-280057- Mesoscale Precipitation Discussion 0089 NWS Weather Prediction Center College Park MD 257 PM EDT Thu Mar 27 2025 Areas affected...Deep South TX Concerning...Heavy rainfall...Flash flooding likely Valid 271857Z - 280057Z SUMMARY...A strong and well-organized QLCS gradually settling down through Deep South TX will be capable of producing very heavy rainfall rates and a general likelihood for flash flooding heading into the early evening hours. DISCUSSION...GOES-E IR satellite imagery in conjunction with dual-pol radar shows a well-defined QLCS gradually settling eastward down across Deep South TX. This convective complex is being strongly favored by the ejection of left-exit region upper-level jet dynamics across the lower Rio Grande Valley downstream of a deeper layer trough crossing northern Mexico and parts of the southern High Plains. This energy is also interacting with a quasi-stationary frontal zone and the pooling of a modestly unstable airmass characterized by MLCAPE values of near 1000 J/kg. While instability is rather modest, there is a rather favorable shear environment for a continuation of organized convection over Deep South TX with stronger mid-level winds helping to support as much as 40+ kts of effective bulk shear. Some additional uptick in diurnal heating over the next few hours should support some additional boundary layer destabilization and this coupled with a convergent and moist low-level south-southeasterly jet of 30 to 40 kts should support convection with high rainfall rates capable of reaching 2 to 3 inches/hour with the stronger storms. In fact, the latest CIRA-ALPW data shows a notable surge/wave of higher PWs/moisture concentrated in the SFC/850 mb layer lifting northwest out of the Bay of Campeche and taking aim on Deep South TX. Speed convergence associated with this in conjunction with the implied stronger moisture transport will further enhance the rainfall rate potential over the next few hours. The 12Z HREF guidance along with numerous runs of the HRRR continue to struggle with the details and evolution of the ongoing convective activity more regionally over southern TX. Accounting for the current activity, the HRRR is closest from a convective mode/object perspective, but is way too slow with its evolution. Basically the HRRR 00Z to 06Z/Fri QPF signal is likely to occur more over the next 6-hours based on the latest satellite and radar trends. High rainfall rates and rather slow cell-motions with the QLCS evolution should favor additional rainfall amounts of as much as 3 to 5 inches, and especially where any transient areas of cell-training can occur. Given the wet antecedent conditions from earlier heavy rainfall, these additional rains are likely to cause additional areas of flash flooding heading into the early evening hours, and this will include the Brownsville vicinity. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9lJw7qhr-YditUF01Jsskdf0F1HyOx-VligRuIWX7GghXyGUKavp5zBbEsD-Qg8grHcs= y4kj0RwOjuo95XTSHkADn00$ for graphic product... ATTN...WFO...BRO...CRP... ATTN...RFC...WGRFC...NWC... LAT...LON 27509751 27429722 26879728 25919702 25739713=20 25959801 26199884 26569899 27159840=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .