Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Jun 23 2023 16:38:55 AWUS01 KWNH 231638 FFGMPD LAZ000-TXZ000-232200- Mesoscale Precipitation Discussion 0570 NWS Weather Prediction Center College Park MD 1238 PM EDT Fri Jun 23 2023 Areas affected...Coastal Louisiana and far Southeast Texas Concerning...Heavy rainfall...Flash flooding possible Valid 231637Z - 232200Z Summary...Slow moving thunderstorms will increase in coverage along the Gulf Coast this afternoon. Rainfall rates of 2-3"/hr are expected, which through slow motions could produce 3-5" of rain. Isolated flash flooding is possible. Discussion...The regional radar mosaic early this aftn indicates a slow expansion of nearly stationary thunderstorms along the Louisiana coast and into far southeast Texas. These storms are developing in response to convergence along a weakening stationary front just inland from the Gulf of Mexico, with additional ascent being provided by an approaching shortwave noted in the GOES-E WV imagery. The environment is extremely conducive to heavy rain as PW measured by the 12Z U/A sounding at KLCH was 2.04 inches, above the 90th percentile for the date, combines with U/A measured and RAP analyzed MUCAPE of more than 2000 J/kg. Blossoming convection has had estimated rain rates of 1.5 to 2 inches/hr already, with chaotic cell motions around 10 kts. As the shortwave continues southward it will impinge into an airmass that will become even more favorable for ascent due to increasing instability and onshore flow driving PWs as high as 2.25 inches according to the RAP. The overlap of weak height falls, convergence along the front, and diurnally increasing CAPE should result in scattered thunderstorms. The high res is struggling to capture ongoing convection, so its simulated reflectivity is somewhat sparse, but the ingredients suggest more widespread coverage this aftn than being depicted in the models this morning. Mean 0-6km winds will remain 10-15 kts from the NW, which should interact with the onshore flow south of the front to collapse Corfidi vectors to just around 5 kts. This suggests storms will be slow movers, or even potentially stall at times, and with rain rates of 2-3"/hr expected, could produce 3-5" of rain in some areas as reflected by HREF neighborhood probabilities. Some of this rain could fall in a very short period of time as well, noted by HRRR 15-min rainfall as high as 0.75 to 1+ inches. In general the soils across this area are dry from recent below normal rainfall leading to FFG that is as high as 2.5"/1hr and 3"/3hrs. This suggests that most areas should be able to handle this rainfall. However, an isolated flash flood risk exists as these rain rates could still overwhelm soils, especially where any storms can linger to increase intense rain rate duration. Any flash flooding will be most likely atop more urban areas, but could occur anywhere across the region through the aftn. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!77UBQ7UmBCjT4zVOwLIbGlZETtjaujRui5TuD5qNkiLGovK9lBnmTCQkyUsUpECsyYct= SBwoc5-DynO9pZ18HitqlRY$ for graphic product... ATTN...WFO...HGX...LCH...LIX... ATTN...RFC...LMRFC...WGRFC...NWC... LAT...LON 30519401 30419291 30279157 30219107 30089035=20 29998986 29888945 29578906 29258892 29048901=20 28888941 28979039 29139146 29199219 29279329=20 29379441 29549463 29889476 30209458 30469408=20 =20=20=20=20=20=20=20=20=20=20=20=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) .