Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Sep 27 2024 21:31:19 AWUS01 KWNH 272131 FFGMPD DEZ000-MDZ000-VAZ000-NCZ000-280201- Mesoscale Precipitation Discussion 1079 NWS Weather Prediction Center College Park MD 530 PM EDT Fri Sep 27 2024 Areas affected...Southeast VA, eastern MD, far southern DE Concerning...Heavy rainfall...Flash flooding possible Valid 272130Z - 280201Z Summary...Clusters of showers and thunderstorms with 2-3"/hr rain rates continue to lift northward this evening. Through training, these rates could produce 2-3" of rain with locally higher amounts. Flash flooding is possible. Discussion...The regional radar mosaic early this evening shows a cluster of thunderstorms lifting northward out of far northeast North Carolina towards Richmond and as far north as the Middle Peninsula of VA. These thunderstorms are lifting northward on mean 0-6km winds of around 40 kts, so remain progressive, but are containing MRMS measured hourly rainfall accumulations of 2-2.5 inches. These impressive rain rates are being fueled by an axis of tropical moisture characterized by PWs of 2-2.4 inches, above the daily maximum for the region according to the SPC sounding climatology, funneling northward around the periphery of what is now Post-T.C. Helene over Kentucky. An axis of SBCAPE exceeding 500 J/kg is collocated with this PW plume, providing rich thermodynamics to support continued convection as ascent persists through 850mb wind convergence, modest upper jet diffluence, and a weak shortwave impulse rotating within the flow. This heavy rain has already resulted CREST unit streamflow responses above 500 cfs/smi, leading to multiple active FFWs. The high-res CAMs differ in their evolution the next few hours, but the latest NAMNest appears to be handling the current convective activity the best, followed by the recent run of the HRRR which has caught onto to the eastward shift. These runs suggest convection will persist as it heads north, but will begin to encounter weaker instability into MD/DE. Some of this will be offset by thermodynamic advection as low level 850mb inflow pushes higher PW and instability to the north, but in general this should result in a slow wane of the intensity of this convection. This is reflected as well both by HRRR 15-min rainfall accumulations and HREF neighborhood probabilities for 1-hr rainfall exceeding 1" peaking around 20%. However, as propagation vectors veer to become more aligned into the more rich thermodynamics, this could result in short-term backbuilding and training to lengthen the duration of these rain rates leading to corridors of rainfall that could reach 2-3" in some areas. As long as the intense rain rates persist, they will pose a risk for flash flooding. However, much of eastern MD and DE has been dry recently, leading to elevated FFG that only has a 5-10% chance of being exceeded. This suggests the greatest risk for any impacts will be across SE VA, or where any training can move across an urban area through the evening. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!58W3cin_F4YkP2J__5_J-CiJOa7wa4Omsm_-6tOtquI9E3w5FH3fx4cjnChviSZyme61= z-NO63IO2h5zNFfqtn0m3WA$ for graphic product... ATTN...WFO...AKQ...LWX...PHI... ATTN...RFC...MARFC...SERFC...NWC... LAT...LON 38937572 38847530 38727506 38427502 38047501=20 37617524 37267557 36987568 36677580 36407595=20 36147616 36107656 36277695 36557747 37127763=20 37707746 38437693 38827659 38927623=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) .