Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 09 2023 19:10:19 AWUS01 KWNH 091910 FFGMPD MDZ000-VAZ000-NCZ000-DCZ000-WVZ000-100100- Mesoscale Precipitation Discussion 1046 NWS Weather Prediction Center College Park MD 309 PM EDT Sat Sep 09 2023 Areas affected...Virginia, Maryland Concerning...Heavy rainfall...Flash flooding possible Valid 091908Z - 100100Z Summary...Slow moving thunderstorms developing across the Mid-Atlantic states will persist into this evening. Rainfall rates of 1-2"/hr are likely, which through slow motions could produce 2-4" of rainfall. Flash flooding is possible, most likely in urban areas. Discussion...The regional radar mosaic this afternoon indicates multiple clusters of thunderstorms lifting across NC/VA/MD. These storms are moving northward within a region of robust thermodynamics characterized by PWs of 1.5-1.7 inches and SBCAPE of 2500-3500 J/kg. A weak, but convectively enhanced shortwave/MCV is noted in WV imagery lifting northward into VA, while an anomalous mid-level trough centered over the TN VLY shifts slowly eastward driving modest height falls across the region. A weak upper jet streak pivoting northward downstream of this trough axis is enhancing ascent as well through its diffluent LFQ. With nearly unidirectional flow from the sfc-200mb noted in morning U/A soundings, pronounced moist advection will persist, and it is likely even more widespread thunderstorms will impact the region through this evening. Rainfall rates already today have been estimated to be 2.5-3"/hr from KLWX, which has resulted in more than 2.5 inches of rainfall at a few mesonet sites near Washington, D.C. Unfortunately, the high-res guidance is struggling with the activity across MD this aftn, so confidence is slightly below average. It is likely that the pool of impressive SBCAPE around the Chesapeake Bay and extending towards I-95, along with locally higher PWs, are not being sampled by the high-res guidance, resulting in the lack of activity in this area. Radar trends and the SPC RAP analysis suggest these storms will continue to re-fire along the intense instability gradient, with Corfidi vectors likely collapsing to near zero as storms build back to the S/SE into the higher instability. This may persist until the robust convection lifting out of NC/VA, which is reflected by the high-res simulated radar, lifts north by this evening. Rainfall rates within any of these thunderstorms could produce 3"/hr rates (HRRR 15-min rainfall as high as 0.75"), which through training and/or slow storm motions could result in 2-4" of rainfall. Although the HREF and RRFS probabilities for more than 3" are limited, the ingredients and environment suggest some locations across MD/N VA could approach 5" of rainfall by this evening. 14-day rainfall has been well below normal according to AHPS, which has led to FFG as high as 4"/3hrs across most of the area. While exceedance of these probabilities is less than 5% according to the HREF, which again is struggling, it is possible that rapid runoff and flash flood instances will occur where the most intense training or multiple rounds of heavy rainfall occur. While flash flooding is possible anywhere across this area this evening, it will be most likely should training occur in the less permeable urban areas. Weiss/Snell ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6yyDYQV-fKxg_pfrR9BaXYEUIMJP1Lswq0DAtmK9wVWbaQZ1Fs1MR1q0xvuuBqzlxIiJ= bib6OMLUELK3rQqBcHwLx8g$ for graphic product... ATTN...WFO...AKQ...LWX...RAH...RNK... ATTN...RFC...MARFC...SERFC...NWC... LAT...LON 39637803 39597682 38707639 37757612 36827591=20 36497616 36437699 36497799 36737920 37357967=20 38157925 39087859=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) .