Subj : MESO: Heavy rain/Flooding To : All From : Mike Powell Date : Fri Jan 26 2024 08:55:00 AWUS01 KWNH 260958 FFGMPD MSZ000-LAZ000-261555- Mesoscale Precipitation Discussion 0034 NWS Weather Prediction Center College Park MD 457 AM EST Fri Jan 26 2024 Areas affected...southeastern LA into southern MS Concerning...Heavy rainfall...Flash flooding possible Valid 260955Z - 261555Z SUMMARY...An increase of heavy rain with periods of training is expected early this morning across southeastern LA into southern MS. Flash flooding will be possible from rainfall rates to potentially peak in the 1-2 in/hr range, falling on top of locations which received heavy rain with in the past 2 days. DISCUSSION...0930Z GOES East infrared satellite imagery with lightning data overlaid showed a cluster of thunderstorms 50 to 150 miles south of the eastern LA coast. Longer loops of satellite data with surface observations overlaid showed the presence of a composite outflow boundary in the central Gulf of Mexico (south and east of the thunderstorm cluster). However, station plots in the northern Gulf have largely returned back to southerly flow, helping the advection of low level moisture back toward the central Gulf Coast and making the outflow's presence less impactful. Of key importance, the 850-700 mb layer in LPW imagery has shown a notable northward advance of higher moisture across southern LA since 05Z. Given the mid-levels are not likely to have significantly changed since 00Z, the 700-500 mb lapse rate from 00Z LIX sounding showing 7 C/km is likely still valid across the central Gulf Coast region. As an upper level shortwave trough continues to advance east from eastern TX over the next 6 hours, low level winds in the 925-850 mb layer out ahead of the upper trough across the central Gulf Coast are expected to back, helping further with the transport of low level moisture into southeastern LA and southern MS, eroding a dry layer seen on the 00Z sounding from LIX and recent RAP analysis point soundings in the area. Given fairly steep mid-level lapse rates, low level moisture advection should result in the rapid development of uninhibited MUCAPE of 500 to 1000+ J/kg later this morning. Low level warm advection beneath the divergent right entrance region of a 100-120 kt 250 mb jet max is likely to support the increase of showers and thunderstorms, perhaps as early as 12Z, across southern LA into southern MS. Southwesterly steering flow may align with similarly oriented low level convergent axes in the 925-850 mb layer, supporting periods of training. While there remains uncertainty with convective vigor, especially with recent runs of the HRRR backing off on QPF totals through 15Z, the thermodynamic and kinematic environment will be capable of 1-2 in/hr rainfall rates. According to Multi-Sensor MRMS estimates, 4 to 8 inches of rain has fallen over portions of central/southern LA into southern MS within the past 48 hours. This had led to saturated soils in some locations which will be more vulnerable to flash flooding from additional heavy rainfall. The possible addition of 1 to 3 inches of rainfall through 16Z may lead to renewed areas of flash flooding across southeastern LA into southern MS. Otto ATTN...WFO...JAN...LCH...LIX...MOB... ATTN...RFC...LMRFC...NWC... LAT...LON 31398952 30778919 30008916 29189008 28949084 29199160 29339265 29729268 30219182 30579123 31349022 = = = --- SBBSecho 3.14-Linux * Origin: Ilink: CCO - capitolcityonline.net (454:1/105) .