Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Dec 02 2023 04:28:30 AWUS01 KWNH 020428 FFGMPD MSZ000-LAZ000-021030- Mesoscale Precipitation Discussion 1185 NWS Weather Prediction Center College Park MD 1127 PM EST Fri Dec 01 2023 Areas affected...Portions of South-Central to Southeastern Louisiana Concerning...Heavy rainfall...Flash flooding likely Valid 020430Z - 021030Z Summary...Isolated to scattered instances of flash flooding are likely overnight with localized rainfall rates of 1-2"/hr leading to additional rainfall totals of 2-5". Discussion...Areas of heavy rainfall are ongoing once again this evening across portions of south-central to southeastern LA, as a stalling cold front allows for localized training of 1-2"/hr rainfall rates. The mesoscale environment is otherwise characterized by precipitable water of 1.5-1.8" (at or above the 90th percentile for early December, per LIX sounding climatology), surface-based and mixed-layer CAPE of 500-1000 J/kg (but gradually decreasing), and ample deep layer shear of 50-60 kts. While decreasing instability should generally favor weakening of convection into the overnight, this looks to be somewhat offset by a diurnally strengthening southwesterly low-level jet (going from 20-25 kts to 30-35 kts at 850 mb, increasing associated moisture transport and allowing for localized training due to the stalling cold front to the west). These heavy rainfall rates are partially overlapping areas that have already seen 2-6" of rainfall over the past 24 hours, but the vast majority of that heavy rainfall occurred more than 12 hours ago. Given this is the often rain-soaked Gulf coast of LA, flash flood guidance has largely recovered with 1-3 hr thresholds generally ranging from 2-3". With rainfall rates of 1-2"/hr expected to continue, localized 3-hr totals are expected to range from 2-4" (with a few spots reaching as much as 5" over the next 6 hours), which will likely lead to isolated to scattered instances of flash flooding (with the populated portions of the Lafayette and Baton Rouge metro areas along I-10 particularly vulnerable, given the urbanized terrain and aforementioned 2-6" rainfall totals). The threat will persist through the early morning hours, gradually coming to an end around 10-11z as the lack of remaining instability will struggle to support showers with even 1"/hr rainfall rates.=20 Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!-K5ELWsrOspAVdaonfv9Nwku6ucYUWsSnfeYgk1RMv8itN-VD_7J0vUkCgqJDt7-8AAU= n_UZfAqXa8YvyGf3CafST9s$ for graphic product... ATTN...WFO...LCH...LIX... ATTN...RFC...LMRFC...NWC... LAT...LON 30729046 30668982 30008975 29609063 29409126=20 29389174 29459191 29639206 29839197 30119180=20 30299152=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) .