Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri May 02 2025 18:11:00 AWUS01 KWNH 021810 FFGMPD LAZ000-TXZ000-030000- Mesoscale Precipitation Discussion 0210 NWS Weather Prediction Center College Park MD 209 PM EDT Fri May 02 2025 Areas affected...portions of central and eastern TX through western LA Concerning...Heavy rainfall...Flash flooding possible Valid 021800Z - 030000Z Summary...Convection will continue to proliferate this afternoon, likely resulting in scattered totals of 3-5" (and locally higher) through the evening. Scattered to numerous instances of flash flooding are possible, and may be locally significant in more sensitive terrain and metro areas. Discussion...Convection is beginning to proliferate across portions of eastern TX, as 20-30 kts of southerly to southeasterly low-level (925-850 mb) moisture transport combines with relatively moist, cool air aloft (700-500 mb) originating from convection over the northern Sierra Madre Oriental range yesterday (as is clear from CIRA advected layered precipitable water imagery). While this region just north and east of the Houston metro area is the current core of the highest moisture content (PWATs near 1.8", per SPC's SFCOA analysis, which is well above the 90th percentile per LCH sounding climatology), the broader region from the Heart of TX northeastward to the Ark-La-Tex is characterized by PWATs of 1.4-1.8", SB CAPE of 2000-4500 J/kg (with a tight gradient along the northern extent due to relatively stable outflow from an MCS near the Red River of the South overnight), and effective bulk shear of 25-40 kts. Shear is resulting from a dual jet structure that is somewhat phased, providing ample divergence aloft within the left-exit region of a subtropical jet streak (near the TX/Mexico border) and on the outer periphery of a right-entrance region of a polar jet streak (centered over the Great Lakes). Convection is anticipated to continue to proliferate, likely growing upscale to the north and west as the afternoon progresses. Relatively broad surface to low-level convergence should become more defined over time, reinforced by the aforementioned outflow sagging south (along with a quasi-stationary front lagging just behind with additional ongoing convection inbetween). Recent hi-res guidance (12z HREF suite) is in rather good agreement concerning the potential for excessive rainfall, indicating relatively high odds (40-70%) for localized 3" exceedance and somewhat elevated odds (15-25%) for localized 5" exceedance (per 12z HREF 40-km neighborhood exceedance probabilities). Subsequent HRRR and experimental RRFS hourly runs (since 12z) support the earlier ensemble guidance, consistently indicating the potental for 6"+ localized totals over the next 6 hours (through 00z). While scattered 3-5" totals (with locally higher amounts) are likely, corresponding Flash Flood Guidance (over a 3-6 hour period) largely encompasses the same range (3.0-5.0"). This suggests that scattered to numerous instances of flash flooding are possible (though not guarenteed). The situation is more concerning for sensitive terrain, including eastern portions of the TX Hill Country into the Heart of TX (including the San Antonio and Austin metro areas) where FFGs are as low as 2.0-3.0", and perhaps most concerning for portions of the Houston/Galveston metro into the Golden Triangle region of southeast TX (where HREF exceedance probs are maximized). Should higher totals occur over more sensitive areas, significant to life threatening flash flooding is possible. Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7QYwxzKqJcY2TZlclXwM356aOX_msIpb5Ij50AkD2-sotN2-OdcFdTLwnvJz50ar27kq= V7CUrfHpcQqC1UHMUPhz5Lc$ for graphic product... ATTN...WFO...EWX...FWD...HGX...LCH...SHV...SJT... ATTN...RFC...LMRFC...WGRFC...NWC... LAT...LON 32889352 32289295 31439295 30139323 29739402=20 29369579 29069721 29449899 30889914 31409846=20 31579720 31959577 32289510 32609454=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) .