Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 17 2025 04:02:02 AWUS01 KWNH 170401 FFGMPD NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-170900- Mesoscale Precipitation Discussion 0720 NWS Weather Prediction Center College Park MD 1201 AM EDT Thu Jul 17 2025 Areas affected...Central & Southeast PA...Maryland...DC...Northern and Northwest VA...Northern DE...Far Soutwest NJ... Concerning...Heavy rainfall...Flash flooding possible Valid 170400Z - 170900Z SUMMARY...Larger scale conditions improving, but scattered strong cells along secondary squall line may cross already/currently flooding areas and very low FFGs with additional quick 1-2" sub-hourly total with another round of possible localized flash flooding. DISCUSSION...GOES-E WV and 500mb analysis shows a stack of phasing shortwave centers from the northern most rapidly progressing across MN, a second crossing the LP of MI and the third leading southern stream wave still amplifying over Upstate NY. The lead wave resulted in strong thunderstorms that left many locations across the Mid-Atlantic with high rates and totals with scattered flash flooding with MRMS Crest unit Stream flows dotted across the region still over 200-500 cfs/smi with greatest concentration from Wilmington DE across the Capitol District into northern VA. Most cells have weakened with reduced convergence and loss of instability but lingering into the Delmarva.=20 The second wave has stronger, more progressive height falls with strong 850-700mb effective cold front pressing in a much drier low to mid-level air mass out of the Ohio Valley. Still, strong southerly (though has not really backed much still affected by the leading wave) maintains solid moisture flux with well above average moisture values of 2-2.25" advected northward into far southeast PA/NJ and Maryland, but remains connected across the VA Piedmont region. A core of moisture near the effective triple point to this wave is over-topping the Allegheny Plateau into central PA providing a bit further moisture flux convergence with about 30-40 degrees and 30-40kts of convergence to maintain scattered stronger cells along the line. GOES 10.3um shows tops are generally warming, but still a few isolated overshooting tops dot through the line. Cells are progressive and rates are reducing; which is to be expected with loss of day time heating and mixing from initial round. But an additional quick burst of 1" in a sub-hourly manner over flooded areas remains a problem for reaggrivation of flooded rivers, creeks and roads in the area still flooded from the first round. So while coverage and magnitude of flash flooding is likely to be lower end, the risk remains for the next few hours. Much of the central VA Piedmont missed out from the initial round, this has left an area of untapped conditionally unstable air that has advected northward in the wake of the initial cells along the eastern slopes of the Blue Ridge into Northern VA/MD. A weak east to west outflow boundary does exist across northern VA into far southern MD; a few Hi-Res CAM guidance members suggest moisture flux convergence and isentropic ascent over this boundary may trigger additional newer/stronger cells that may orient along the boundary for some repeating training in proximity of areas affected earlier tonight in N VA, DC and central MD. Given this risk, the MPD is expanded across this region on a low confidence potential for additional 2-3" totals. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9DW8en6Exf0yb8lQaLwm5VJsoXjIk0prqRCG7XE-Lj2isXTjKx-kS1B8nm9Z1E-p9TNZ= OJtVRLDXZeQusCHkSyTr4lA$ for graphic product... ATTN...WFO...CTP...LWX...PHI...RNK... ATTN...RFC...RHA...NWC... LAT...LON 41197820 41097680 40647588 40337544 40017504=20 39467497 38927528 38697606 38627648 38287793=20 37797882 37557948 38137990 38887912 40037869=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 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .