Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 18 2024 15:02:34 AWUS01 KWNH 181502 FFGMPD VAZ000-NCZ000-182100- Mesoscale Precipitation Discussion 0648 NWS Weather Prediction Center College Park MD 1101 AM EDT Thu Jul 18 2024 Areas affected...Southeast Virginia and Northeast North Carolina Concerning...Heavy rainfall...Flash flooding possible Valid 181500Z - 182100Z Summary...Thunderstorms are expected to begin developing around midday and into the early afternoon. These storms may move slowly and train over the same areas, leading to an increasing risk of flash flooding. Rain rates could approach or even exceed 3 inches per hour. The area of greatest concern is in far southeast Virginia, near Norfolk, and in far northeast North Carolina, but the potential for flash flooding will extend along much of the VA-NC border region into the afternoon. Discussion...A concentrated area of organized convection is expected to initiate and expand in coverage and intensity in the next few hours. Some hi-res models take a longer time to ramp up convective coverage, but 12Z soundings from WAL and MHX both already indicated strong instability with limited CINH, so the expectation is that an earlier onset in the 16-18Z time frame is more likely. Between 18Z and 21Z, HREF probabilities of exceeding flash flood guidance and 2-3 inch per hour rain rates increase markedly. The potential for extreme rain rates approaching or exceeding 3 inches per hour seems well supported by observational evidence. In particular, the combination of CAPE in excess of 2000 j/kg and PWs well in excess of 2 inches usually yields very high instantaneous rain rates, and the mean flow is weak enough today to support greater persistence of convection in any one location. The PWs in far SE VA and far NE NC are generally above the 95th percentile, even for mid-July, and melting level and WBZ heights are also generally above the 90th percentile for this time of year. Abundant moisture and deep warm cloud layers would tend to support more efficient rainfall production as well. The area of greatest concern seems to be in the Tidewater region of far southeast Virginia and far northeast North Carolina, including the greater Norfolk area and the area around Albermarle Sound. Flash flood guidance is a little lower in these areas, but perhaps more importantly this is also the area with the strongest instability and highest PW values, thereby also generally favoring the highest rain rates. Most 12Z hi-res guidance suggests a progressive line of storms eventually pushing across the area between 21Z and 00Z, but the primary concern for flash flooding would be convection that can initiate and organize ahead of that. The hi-res guidance seems to favor areas along and near the sounds of the region, and likely enhanced convergence along any sound breezes that may develop in the early afternoon. Lamers ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_5wybJyERsbMngPwHlFD4s2iu-S757jwof5O3TlaquME7e1Ofbp9bAToMvg0SSmhKEJn= XzT-gaadAxL8LXgXNfpsoPo$ for graphic product... ATTN...WFO...AKQ...MHX...RAH...RNK... ATTN...RFC...MARFC...SERFC...NWC... LAT...LON 37397838 37357725 37297606 36027559 35577603=20 35467693 35807775 35887882 35848017 36648029=20 37067921=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) .