Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 22 2024 05:18:08 AWUS01 KWNH 220518 FFGMPD VAZ000-NCZ000-SCZ000-221000- Mesoscale Precipitation Discussion 0688 NWS Weather Prediction Center College Park MD 117 AM EDT Mon Jul 22 2024 Areas affected...Midlands and Upstate SC through the Piedmont of southern VA Concerning...Heavy rainfall...Flash flooding possible Valid 220516Z - 221000Z Summary...Showers and thunderstorms will continue to develop and track northeast overnight. Rainfall rates of 2-3"/hr are likely at times, which could produce an additional 1-3" of rain with locally higher amounts. This rain falling atop saturated soils could produce flash flooding. Discussion...The regional radar mosaic this morning shows a cluster of thunderstorms from the Midlands of SC northward along the Piedmont of NC. These storms are lifting northward in response to a convectively enhanced shortwave, with a secondary impulse noted in GOES-E WV lifting out of GA. Aloft, a modest 70kt jet streak is draped across PA, leaving the favorable diffluent RRQ/tail over the Carolinas, while a warm front is analyzed lifting into central VA. Additionally, 850mb winds feature confluence into the Piedmont, as both Gulf and Atlantic moisture streams surge into the region. The accompanying LLJ is helping to enhance ascent through confluence, but also is drawing impressive thermodynamics characterized by PWs of 2-2.2 inches and MUCAPE of around 2000 J/kg northward. The result of all this has been rainfall rates estimated via local radars as high as 2.5"/hr, leading to MRMS FLASH unit streamflow of 100-300 cfs/smi. The most recent CAMs are generally struggling with the current activity, with both the HRRR and RRFSp1 suggesting convection will rapidly erode in the next few hours. Although RAP 3-hr MUCAPE change suggests convective overturning is stabilizing the environment, it is likely that the continued moisture surge and thermodynamic resupply on the LLJ will enable the upper impulses to maintain and potentially even expand convection overnight. This suggests that the ARW/ARW2 solutions may be more reasonable, which depict a slow northward advance of thunderstorms with additional development beginning across SC. The favorable environment will support heavy rainfall rates in any thunderstorms that do develop, as reflected by 30% HREF probabilities for 2"/hr rates. Locally higher rates are probable as well, as warm cloud depths of 12000-14000 ft combine with deep moist adiabatic lapse rates present in the 00Z GSO/FFC soundings to promote efficient warm rain processes. Although mean cloud layer winds should be progressive at 15-25 kts, the subtle impulses aloft acting upon the favorable thermodynamics will support multiple rounds of convection which could produce 1-3" of rain, with a 20-30% chance of more than 3 inches in some areas. This additional heavy rain will be falling atop soils that are sensitive due to recent rain that has been more than 300% of normal the past 7 days according to AHPS, compromising FFG to as low 2-2.5"/3hrs. The HREF indicates a 20-40% chance of exceedance of this FFG, so if any of these heavy rates fall atop the more vulnerable soils, or if any location experiences multiple rounds of convection, flash flooding could be the result. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6qgBdgauwgdt-Rhfrbtc33NzGeC-XxSGtAutsFpM3NK1g704wvTFJj1Lcd1CTeL7ErkW= etegTJVk_otWunQIvQfnKB4$ for graphic product... ATTN...WFO...AKQ...CAE...GSP...ILM...LWX...MHX...RAH...RNK... ATTN...RFC...MARFC...OHRFC...SERFC...NWC... LAT...LON 37667881 37367782 37017767 36047737 35147789=20 34547878 34207980 34048091 34128168 34338223=20 34778245 35188213 35498146 36198064 37488007=20 =20=20=20=20=20=20=20=20=20=20=20=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) .