Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Sep 04 2023 17:45:11 AWUS01 KWNH 041745 FFGMPD MSZ000-LAZ000-ARZ000-TXZ000-042343- Mesoscale Precipitation Discussion 1035 NWS Weather Prediction Center College Park MD 144 PM EDT Mon Sep 04 2023 Areas affected...Far Eastern TX...LA...AR Concerning...Heavy rainfall...Flash flooding possible Valid 041743Z - 042343Z SUMMARY...Scattered slow-moving areas of heavy showers and thunderstorms this afternoon will pose an isolated threat of mainly urban flash flooding. DISCUSSION...The latest GOES-E WV suite shows a well-defined upper-level low circulation over the Lower MS Valley with some weak vort energy rotating through the base of it. This energy going through the afternoon hours will be interacting with strong diurnal heating and a very moist airmass for at least scattered areas of heavy showers and thunderstorms. Already the airmass over much of the Lower MS Valley region is moderate to strongly unstable with MLCAPE values of 1500 to 2500 J/kg. Meanwhile, deeper layer southerly flow off the Gulf of Mexico is allowing for a tropical environment with PWs of 1.75 to locally just over 2 inches. Radar imagery has been showing a gradual uptick in convection over areas of far eastern TX along a weak low-level trough axis/convergence zone, and this is also rather close to a vort max seen lifting out of the base of the broader upper trough. Additionally, there is a separate low-level trough/weak front lingering over southeast LA which has been a focus for convection over the last few hours, and with some recent uptick in concentration of the activity. Over the next several hours heading through the afternoon, there should be some additional expansion of convection more broadly over the Lower MS Valley and especially since there should be some modest dynamical support/divergent flow aloft associated with the nearby vort energy and larger scale upper-level low center. Some modest effective bulk shear parameters will be in place as well to help provide at least some loose convective organization. Expect rainfall rates with some of these slow-moving storms to be on the order of 2 to 3"/hour. In fact, Slidell, LA (KASD) just picked up 2.54" in the last hour. The 12Z HREF guidance suggests a lot of disorganization to the convection through the afternoon, but the cells should be slow-moving and capable of producing locally very heavy totals. Some spotty 3 to 5 inch rainfall totals will be possible. While antecedent conditions are quite dry, these heavy rains will pose an isolated flash flood threat, and especially for the urban corridors. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!59VqTBu2CawOZdrkysQyOXLphJ_ns-SvjVQy_BbZ74jShWzYd41CexoG-SkP7v7h44pv= slWGNRZZDPqJSTxQjHqs8hQ$ for graphic product... ATTN...WFO...HGX...JAN...LCH...LIX...LZK...MEG...SHV...TSA... ATTN...RFC...ABRFC...LMRFC...WGRFC...NWC... LAT...LON 36489204 35999069 34929063 34019094 32969113=20 31839069 31018972 30198945 29498989 29389089=20 29779222 29829339 29509463 29899529 30489536=20 31809490 32849446 34329408 35649403 36319338=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) .