Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Wed Jul 09 2025 18:52:38 AWUS01 KWNH 091852 FFGMPD NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-NCZ000-DCZ000-WVZ000-100050- Mesoscale Precipitation Discussion 0629 NWS Weather Prediction Center College Park MD 250 PM EDT Wed Jul 09 2025 Areas affected...Mid-Atlantic States Concerning...Heavy rainfall...Flash flooding likely Valid 091850Z - 100050Z SUMMARY...Heavy showers and thunderstorms will evolve across much of the Mid-Atlantic region going into the evening hours. Relatively wet antecedent conditions coupled with high rainfall rates and some cell-training concerns will drive an elevated flash flooding risk, with potential for locally significant and dangerous urban flash flooding. DISCUSSION...The latest GOES-E IR satellite imagery shows an expansive area of cooling convective tops associated with heavy showers and thunderstorms across the central Appalachians which are gradually advancing off to the east as an upstream shortwave trough over the OH Valley encroaches upon the region. The airmass downstream over a large portion of the Mid-Atlantic region is moderate to strongly unstable with MLCAPE values of 1500 to 3000+ J/kg noted east of the Blue Ridge and extending toward the broader Chesapeake Bay region including portions of the Delmarva. A very moist environment is in place with PWs of 1.75 to 2 inches, which includes a 1.82 inch PW in the 12Z IAD RAOB sounding. These PWs are on the order of 1.5 to 2 standard deviations above normal. This very favorable thermodynamic environment is going to combine with a gradually increasing level of deeper layer shear over the next several hours as stronger mid-level west-southwest flow arrives ahead of the upstream shortwave. In fact, at least for the central and and northern Mid-Atlantic, including northern VA and central MD east through the northern Delmarva, southeast PA and southern NJ, there will be as much as 30 to 40 kts of effective bulk shear. This will promote numerous areas of multi-cell and perhaps some localized supercell thunderstorm activity near and east of the Blue Ridge, and extending through the greater Chesapeake Bay region going through the remainder of the afternoon and early evening hours. High rainfall rates are expected given the organized nature of the convective threat along with the very moist and unstable environment. The latest hires CAM guidance supports rainfall rates of locally as high as 1.5 to 2.5 inches/hour with the stronger cells. The convective evolution in time should take on a more progressive/linear mode, but as this occurs there may be some localized corridors of cell-training. This will yield locally higher-end rainfall potential with some spotty storm totals of 3 to 5 inches not out of the question. This is supported by the 12Z HREF and 06Z REFS guidance. This rainfall potential over the next several hours coupled with generally wet antecedent conditions and the highly sensitive urban areas of the Mid-Atlantic, including the I-81, I-64 and I-95 corridors from southwest to northern VA, central MD and southeast PA, will favor an elevated risk of flash flooding. This will include concerns for locally significant and dangerous urban flash flooding for several major metropolitan areas. Orrison/Shieh ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!_4kcZPVj-I0_f-v_rTRNV3b2DymOIUUkcbGXZZwkJGIBLmOWjQ868V4UFtFnlp7fzGxr= Vioz_qQk6BpKdHc3wFBhLnM$ for graphic product... ATTN...WFO...AKQ...CTP...GSP...LWX...PHI...RAH...RLX...RNK... ATTN...RFC...ALR...RHA...TIR...NWC... LAT...LON 40337512 40107433 39367429 38507518 37867607=20 36847810 35447979 35428088 36288122 37998022=20 39157876 40137665=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) .