Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jun 14 2023 05:19:24 AWUS01 KWNH 140519 FFGMPD MSZ000-LAZ000-ARZ000-TXZ000-OKZ000-141115- Mesoscale Precipitation Discussion 0479 NWS Weather Prediction Center College Park MD 118 AM EDT Wed Jun 14 2023 Areas affected...Far Northeast TX...Southern AR...Northern LA...North-Central MS Concerning...Heavy rainfall...Flash flooding likely Valid 140515Z - 141115Z Summary...Strong to severe thunderstorms will continue to produce 1-2"/hr rates overnight, resulting in additional localized totals of 2-4". Isolated to scattered instances of flash flooding are likely. Discussion...Strong to severe thunderstorms are ongoing late tonight across portions of the Ark-La-Tex, with hourly accumulations of 1-2" being fairly common (per MRMS estimates) in association with the strongest supercells over the past several hours. Storms are expected to persist for the remainder of the overnight, and semi-discrete cells may also become more organized into a convective complex as a shortwave trough to the northwest (centered near northeast OK) digs into the region. The mesoscale environment is otherwise characterized by MU CAPE of 1500-3000 J/kg, PWATs of 1.4-2.0 inches (near the 90th percentile, per LZK, SHV, and JAN sounding climatology), and most impressively deep layer (0-6 km) bulk shear of 50-60 kts (at or above the max moving average, per LZK, SHV, and JAN sounding climatology). From a heavy rainfall perspective, the biggest limiting factor for excessive rainfall are the storm speeds themselves, as storms have been averaging motions between 35-45 kts. Therefore for the flood threat to become anything but highly isolated/localized, there would need to be a greater coverage of supercells within a training configuration and/or an organization of convection into more of a complex (i.e. MCS). The 00z HREF (subsequent HRRR runs) have been fairly consistent in depicting the Ark-La-Tex (and downstream areas of AR/LA/MS) as the most at-risk area for localized 2" and 3" exceedance through 12z, but there is quite a bit of variation in the ultimate convective evolution and resulting placement of highest QPF. Current thinking is that we will get a bit better coverage of the training of semi-discrete cells initially (with favored right-movers tracking across the AR/LA/MS border region) before the upstream shortwave (and its associated increase in low-level WAA) tries to organize convection more linearly (while ejecting it more quickly eastward into MS). Perhaps the best depiction of this expectation is from the 00z HRRR, whereas the subsequent runs have been much less intense and focused with activity. This run would suggest more concentrated totals of 2-4" (clustered around southern AR and northeastern LA, primarily). This matches up fairly well with the HREF exceedance probabilities (which depict a large area of 30-60% neighborhood probabilities for 2" exceedance, and a smaller area of 30-50% for 3" exceedance). Given that Flash Flood Guidance (FFG) is near 3" for the bulk of the region (with that much haven already fallen for some localities as well), isolated to scattered instances of flash flooding are considered likely. Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_TvMjVBsB3EfQvHB4WzHKfq7E0qHaEMKV2ttjVFFnoM-aMLHiLmX1BfPD_mJF4OI4ZV_= JsRatcHKtE8xMX1WnIVeqkk$ for graphic product... ATTN...WFO...JAN...LZK...MEG...SHV... ATTN...RFC...ABRFC...LMRFC...SERFC...NWC... LAT...LON 34889148 34269008 33748869 32738893 31889029=20 31869147 32389338 33119460 33489523 34159468=20 34409428 34849319=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) .