Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Mar 04 2024 17:30:43 AWUS01 KWNH 041730 FFGMPD MSZ000-LAZ000-042330- Mesoscale Precipitation Discussion 0076 NWS Weather Prediction Center College Park MD 1230 PM EST Mon Mar 04 2024 Areas affected...Much of Louisiana & Adjacent SW Mississippi and E Texas... Concerning...Heavy rainfall...Flash flooding possible Valid 041730Z - 042330Z SUMMARY...Strong, slow moving rotating cells capable of very intense rainfall rates (2-2.5"/hr) pose short-term totals possibly inducing localized flash flooding. DISCUSSION...Regional RADAR and GOES-E imagery suite depicts broad area of widely scattered thunderstorms starting to sprout through low level cloudy conditions across Louisiana. Solid warm-advective regime with southeasterly surface veering quickly to south and south-southwest into the 850-700mb layer is providing ample theta-E advection in combination with solid low level moisture flux convergence bisecting LA from SE to NW. GOES-WV suite and VWP/RAP analysis denotes solid mid to upper level divergence/diffluence just west of apex of mid-level ridging over south-central TX, providing excellent evacuation as well as solid lapse rates for the upper 60s to lower 70Fs surface moisture values into any developing updrafts. CIRA LPW does note that 850-500mb moisture is lagged a bit further south across the northwestern Gulf of Mexico, but will continue to advect throughout the afternoon rising from total PWAT values of 1.3" currently per GPS (1.5" at the coast) eventually toward 1.75" by evening hours.=20 Cell mode will be key toward rainfall efficiency and given bulk shear values, cell rotation and therefore isallobaric moisture influx should load the lower portion of the cells for the potential for efficient rainfall production. 12-15z HRRR solutions suggest discrete cells with capability of 1.25-1.5" in 15-30 minutes are possible with the rotating thunderstorms. Cells across eastern Texas and northern Louisiana will have slight faster cell motions and are probably going to be more scattered/discrete in nature, even with Bunkers right moving propagation vectors being a bit faster than further south from I-10 to the Gulf, this may limit some of the overall totals further north, but isolated 2-3" over a short-duration may still pose localized flash flooding concerns even though soils have been dry (as noted by NASA SPoRT LIS 10-40cm soil moisture below 50%, in the 5-10 percentile for the season). If hard enough, infiltration will be difficult and almost hydrophobic given the high rates.=20 Further south, propagation vectors due to rotation may be very slow, perhaps even support less than 10kt southeasterly propagation with some near stationary motions anchoring along the deeper layer moisture convergence/WAA axis in the realm of possibility between 21-00z. While most of the guidance and observations suggest these stronger cells are likely to be further south into the swamps...there are ample areas at or south of I-10 with urban ground conditions that may quickly flood if the cells stall or even potentially back-build/redevelop upstream along that moisture convergence axis. As such, highly focused but higher totals in excess of 4" are possible with 12z HREF denoting some spots of 30-50% of 5" exceedance by 06z from BTR to MSY and into the Chandeleur Islands. This may occur after the valid time of this MPD, so will continue to watch trends closely for any subsequent required updates. All in all, the discrete nature to the cells requiring stronger cell rotation to support moisture influx as well as slower cell motions while also occurring across urban areas leaves the risk of flash flooding to localized and considered possible given the lower confidence in precision of cell track/location this afternoon into evening.=20=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!4QamdweuSx5PhXmyZyYc52yv8Xf7HKDMkUl2QyC4uQHHNUXnm2Wqa_mJOpEn_zP7CrZ7= 3CEmwXmsvbQkJHrfv8dlx6c$ for graphic product... ATTN...WFO...JAN...LCH...LIX...SHV... ATTN...RFC...LMRFC...WGRFC...NWC... LAT...LON 32989272 32919173 32639125 31919074 31329031=20 30888973 30238900 29588884 29028908 29008986=20 29879117 30919304 31799379 32799360=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .