Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 24 2023 00:58:13 AWUS01 KWNH 240058 FFGMPD NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-240655- Mesoscale Precipitation Discussion 1098 NWS Weather Prediction Center College Park MD 856 PM EDT Sat Sep 23 2023 Areas affected...Eastern Mid-Atlantic Concerning...Heavy rainfall...Flash flooding possible Valid 240055Z - 240655Z SUMMARY...Heavy rains associated with T.D. Ophelia will continue to lift north across the Mid-Atlantic states tonight. Isolated to widely scattered instances of flash flooding will continue to be possible along the path of Ophelia. DISCUSSION...Ophelia was downgraded to a 30 kt tropical depression at 8PM EDT, and at that time the cyclone was centered at 37.0N 77.6W or about 40 miles south-southwest of Richmond, VA. The cyclone is moving north at 8 kts and will begin to gradually turn north-northeast overnight and approach the northern neck of VA after midnight. There still remains a corridor of heavy concentrated rainfall situated around the northern flank of the circulation center, and this is associated with an axis of strong Atlantic moisture transport/convergence working in tandem with a nearby frontal zone and corresponding axis of strong frontogenetical forcing. However, the remaining corridor of instability is over the lower and middle Chesapeake Bay and the Delmarva where there is an axis of MUCAPE reaching locally as high as 500 to 1000 J/kg. Much of this instability is detached from the surface center though and is reflective of a cyclone that is increasingly transitioning to a baroclinic/extratropical system. The 18Z HREF in conjunction with the last few runs of the HRRR guidance support additional rainfall amounts going through 06Z (2AM EDT) of as much as 1 to 3 inches. These totals will generally be confined to the heavy rainfall corridor close to the circulation center track as it approaches the northern neck of VA over the next several hours, and also where any scattered convective bands around the northeast flank of the circulation can focus given the available instability and stronger low-level convergence near the Delmarva. As Ophelia continues to weaken, the flash flood threat will also generally be on the decline. However, sufficient heavy rainfall may continue to promote an urban flash flood threat, and with earlier rainfall today and lowering FFG values, there should still be a regional concern for isolated to widely scattered instances of flash flooding heading into the overnight period. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9f3WGgta4hsMiu5jL9XmWhuIVUYV8s7QC16K3oE2XN1rId4TgFmKy_gnuVhBEcG5wowv= Ai6KPpnKRxmH-sYcywmoh70$ for graphic product... ATTN...WFO...AKQ...CTP...LWX...PHI... ATTN...RFC...MARFC...SERFC...NWC... LAT...LON 40177500 40097412 39727400 38997474 38417514=20 38037614 37067706 36917775 37347827 38167810=20 39187732 39817623=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) .