Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Apr 21 2024 01:33:35 AWUS01 KWNH 210133 FFGMPD LAZ000-TXZ000-210700- Mesoscale Precipitation Discussion 0167 NWS Weather Prediction Center College Park MD 932 PM EDT Sat Apr 20 2024 Areas affected...South-Central Texas through central Louisiana Concerning...Heavy rainfall...Flash flooding possible Valid 210132Z - 210700Z Summary...Showers and thunderstorms with embedded heavy rain rates will expand across eastern Texas tonight before slowly advecting eastward. Rain rates of 1-2"/hr are expected within more intense convection. This will occur atop soils primed from 1-3" of rainfall already this afternoon, leading to the potential for scattered instances of flash flooding. Discussion...The regional radar mosaic this evening depicts an expansion of reflectivity above 40dbZ from near the Rio Grande Valley east-northeast through the Texas Triangle and into central Louisiana. This convection is expanding in response to impressive ascent driven by height falls downstream of an approaching mid-level trough axis, diffluence within the RRQ of a departing upper jet streak, and robust low-level convergence along a sfc-850mb front sagging southward towards the Middle Texas Coast. The associated lift from the overlap of these features is occurring in favorable thermodynamics noted by PWs as high as 1.9", and SPC/RAP MUCAPE of 500-1500 J/kg. This has resulted in moderate to heavy rain across much of this area already this aftn, reflected by MRMS and mesonet observed rainfall of 1 to as much as 3 inches, priming the soils for a slightly greater flash flood risk overnight. As the evening progresses, all of the significant forcing should gradually shift eastward, placing eastern Texas and central Louisiana in the axis of greatest overlap for heavy rain. Local backing of the low-level winds into the stationary front will allow PW advection to persist, and although 850mb wind speeds will remain modest at 10-15 kts, to temper the effective inflow, this will be sufficient in the extremely moist column to support continued convective development with heavy rain. Both the HRRR and HREF sub-hourly fields suggest rain rates of 1-2" will be common overnight, and while this may be overdone due to modest instability, the impressive ascent combined with increasing 0-6km shear to drive convective organization should offset some of this to permit at least periodic rain rates of this intensity. Additionally, Corfidi vectors and mean 0-6km winds aligned to each other and the low-level front suggest training potential which could support an additional 2-3" of rain with locally higher amounts. FFG remains quite high, but has likely been tempered in some areas where HRRR 1cm soil moisture is fully saturated from today's antecedent rain. The 18Z HREF exceedance probabilities for 3-hr FFG did reach 20-30% just inland from the Middle and Upper Texas Coast, but it is probable the true potential is greater than that due to the primed soils. Still, there is some concern that the most intense rain rates will struggle to linger temporally, somewhat limiting the flash flood risk. However, where training can continue, especially over the most saturated soils, flash flooding remains possible. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_JbhbDSlYoSMWubMVowsME9QIsutEdkPc9-adA-g91ZiqiZhdPqTOKFfcZCO3fCJSrWS= 0rRKh2GN6mbp6QcS96Wh3RU$ for graphic product... ATTN...WFO...CRP...EWX...FWD...HGX...JAN...LCH...SHV... ATTN...RFC...LMRFC...WGRFC...NWC... LAT...LON 31809342 31709257 31609212 31409177 31159178=20 31039216 30829295 30499386 29939483 29519587=20 29119689 28799810 28769859 29229886 29779874=20 30449822 31019723 31519617 31779456=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) .