Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Aug 29 2023 00:13:49 AWUS01 KWNH 290013 FFGMPD NCZ000-SCZ000-GAZ000-TNZ000-ALZ000-290545- Mesoscale Precipitation Discussion 0998 NWS Weather Prediction Center College Park MD 813 PM EDT Mon Aug 28 2023 Areas affected...TN Valley into southern Appalachians Concerning...Heavy rainfall...Flash flooding possible Valid 290009Z - 290545Z Summary...Localized hourly accumulations of 1-3" with short-term totals of 2-4" are expected for portions of the TN Valley into the southern Appalachians through ~06Z. A few areas of flash flooding will remain possible across the region. Discussion...Regional radar imagery at 2330Z showed scattered thunderstorms extending from the eastern AL/TN border into portions of western NC and northwestern GA, some of which were slow moving. An elongated outflow boundary was also observed from just east of the Atlanta metro into far northern GA, propagating north and east. MRMS-derived rainfall rates have averaged 1-2 in/hr but have been locally between 2-3 in/hr since 21Z. Recent 850 mb VAD wind plots and fading visible imagery showed a low to mid-level low centered over HUA with nearby wind speeds of ~10 kt or less across the northern half of AL. Farther east, the 850 mb VAD wind plot at KFFC showed southerly winds slightly stronger between 15-20 kt. The low was helping to sustain convection late this evening within an environment characterized by precipitable water values between 1.8 and 2.3 inches along with MLCAPE between 1000-2000 J/kg via the 23Z SPC mesoanalysis. Lift was also being aided by divergence aloft within the right entrance region of a 250 mb jet max located over the central Appalachians. Given the lingering instability across the region, high moisture in place and a forecast for strengthening 850 mb winds into the southern Appalachians to near 20 kt through 03Z, areas of slow moving thunderstorms are expected to continue over the next few hours as the low over northern AL drifts north. Several foci for low level mesoscale convergence combined with a broader region for ascent within the entrance region of the upper jet should promote another 3-5 hours of a flash flood threat across the region. Waning instability by 06Z may bring an end to the larger scale flash flood threat but smaller pockets of instability may still be able to maintain a localized flash flood risk well into the night. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_p07jSuErQdyDQF93MUW1hO7tIxVg65sK5Qi2Tti2PmPlNCgYCVjbDZy6cxGcK7U7QxT= PLKvFnZZ0JFaYGFgq5Tgrr0$ for graphic product... ATTN...WFO...BMX...FFC...GSP...HUN...MRX...OHX...RNK... ATTN...RFC...LMRFC...OHRFC...SERFC...NWC... LAT...LON 36588233 36578165 36438072 35788069 35438129=20 35148240 34548381 34478510 34258589 34268684=20 34878708 35648631 36218510 36488376=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) .