Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Aug 27 2023 06:21:12 AWUS01 KWNH 270621 FFGMPD VAZ000-271220- Mesoscale Precipitation Discussion 0987 NWS Weather Prediction Center College Park MD 220 AM EDT Sun Aug 27 2023 Areas affected...Portions of Central and Southern VA Concerning...Heavy rainfall...Flash flooding possible Valid 270620Z - 271220Z SUMMARY...Slow-moving and highly efficient showers capable of producing 2 inch/hour rainfall rates will pose an urban flash flood threat early this morning. This will include the Richmond metropolitan area. DISCUSSION...Surface data in conjunction with 00Z RAOBs suggests a weak low-level trough is positioned down across areas of central and southern VA in between Farmville (FVX) and Richmond (RIC). This is helping to focus a rather concentrated area of moisture convergence which with the pooling of modest instability (MUCAPE values of 500 to 1000 J/kg) has been yielding some low-topped convection over the last few hours. Some weak frontogenesis in the 1000/850 mb layer is noted as well and this is likely helping to favor some of the recent convective development. The cells are quite shallow though with GOES-E IR satellite data showing cloud top temps generally no colder than about -15C. Thus, a substantial amount of warm rain processes are ongoing and there have already been some 1 to 2 inch/hour rainfall rates noted with these cells. The 00Z HREF guidance supports some very slow-moving convective cells tending to persist through the early morning hours with this rather small-scale axis of low-level forcing/troughing continuing to move very little or perhaps drifting gradually down to the southeast with time. Rainfall rates may continue to approach 2 inches/hour with these showers, and the HREF does support some spotty 3 to 5+ inch totals going through early this morning where the cells tend to persist or locally repeat over the same area. Antecedent conditions are very dry, with high FFG values across this portion of the Mid-Atlantic, so any flash flood threat will generally be isolated and predicated on some of these heavier totals materializing. However, these rains will pose an urban flash flood threat, and this will include the Richmond metropolitan area over the next few hours going through dawn. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7TGhufV6kjrBcQexiaBKcncwkW20Neh8_aBg3Hu6ao7K3PZwq_2tGKPgNQA3XiRzIz4_= TaMJKgsMKcUhm0EIWm_ZcJQ$ for graphic product... ATTN...WFO...AKQ...RNK... ATTN...RFC...MARFC...SERFC...NWC... LAT...LON 37967733 37807682 37397668 37017716 36887798=20 37007856 37237881 37497872 37767838 37957790=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 3.14-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .