Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Sep 13 2023 01:10:59 AWUS01 KWNH 130110 FFGMPD NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-130705- Mesoscale Precipitation Discussion 1062 NWS Weather Prediction Center College Park MD 910 PM EDT Tue Sep 12 2023 Areas affected...northern Mid-Atlantic region Concerning...Heavy rainfall...Flash flooding possible Valid 130108Z - 130705Z Summary...Thunderstorm coverage is expected to increase overnight from northern VA/central MD into eastern PA and adjacent areas of NJ/DE. 1-2 in/hr rainfall rates and a few repeating rounds are expected to overlap with areas that recently received heavy rain, leading to potential flash flooding. Discussion...Local radar imagery from KLWX has shown an increase in the coverage and intensity of thunderstorms over northern VA into central MD over the past hour, located along the leading edge of a surge in low level moisture transport from northern NC into the D.C. metro. 00Z sounding data from IAD showed MLCAPE of ~1000 J/kg while SPC mesoanalysis data from 00Z showed 500-1000 J/kg available from D.C./Baltimore southward into central and southeastern VA. While the 2 inch precipitable water (PW) value reported on the 00Z IAD sounding is overinflated due to precipitation contamination, 1.5 inch PWs were present in GPS data over central and southeastern VA, transporting northeastward on a SSW low level jet. A cold front was analyzed from central NY, southward into far western VA which is forecast to steadily move eastward overnight with increasing 850 mb winds ahead of it, forecast to reach 20 kt over northeastern MD by 06Z. Meanwhile, the northern Mid-Atlantic region was situated within the right entrance region of an upper level jet max located east/southeast of a large closed low centered over the Great Lakes, supporting synoptic scale lift across the region. Thunderstorms are likely to increase and translate northeastward through 06Z, at the nose of the increasing low level jet and increasing instability from the south. While individual cell motions should be progressive toward the northeast at anywhere between 10-25 kt, fairly unidirectional flow from the southwest between the LFC and EL will support areas of training where southwest to northeast echo orientation occurs. Multiple rounds and short term training of heavy rain will support rainfall rates of 1-2 in/hr. Given 3 to 6 inches of rain has fallen across portions of the northern Mid-Atlantic over the past 4-5 days, flash flood guidance is as low as 1 in/hr in several locations. Areas of flash flooding will be possible, especially where overlap of heavy rain occurs with the urban corridor and with any areas that have received heavy rain over the past few days, which will increase the potential for runoff. Otto ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8tM5ouCmXxTVQfsLOSevEwqRhMPeaXYv7RSBBOq9UxrWILjlHxgs91vmzRzrHwoxlZE1= p3hjNexVBeDMQshAXxL7uZQ$ for graphic product... ATTN...WFO...BGM...CTP...LWX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 41497521 41147444 40487431 39557546 38967638=20 38747737 39097780 40037732 40707689 41427612=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) .