Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Jul 31 2025 15:02:03 AWUS01 KWNH 311501 FFGMPD NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-VAZ000-DCZ000-WVZ000-312100- Mesoscale Precipitation Discussion 0832 NWS Weather Prediction Center College Park MD 1101 AM EDT Thu Jul 31 2025 Areas affected...Mid-Atlantic... Concerning...Heavy rainfall...Flash flooding likely Valid 311500Z - 312100Z SUMMARY...Potential for slow moving, highly efficient thunderstorms with localized 2-3"/hr rates possible. Storm interactions may allow for localized totals of 2-4" totals and likely to induce flash flooding conditions by 21z. DISCUSSION...Surface analysis and visible GOES-E imagery shows a well defined stationary front within the Long Island sound intersecting to a surface low in the Delaware Valley before entering the terrain through the Lehigh Valley into south-central PA. A secondary surface wave near MDT/THV has a sharpening Lee Trough extending southward along the lee of the Blue Ridge toward Roanoke, VA and points south. Between the boundaries through the Mid-Atlantic, very moist and building instability can be seen with sfc Tds in the mid-70s with isolated low 80s dotted throughout the area. Weak southerly, confluent flow through 700-500mb is noted in CIRA LPW layers with enhanced moisture which totals over 2" (KIAD already at 2.16" at 12z) and will be increasing toward 2.25+" into the early afternoon. MLCAPE values have reached 2000 J/kg with weak capping noted and visible imagery shows expanding Cu field across much of the area, with some weak vertical development along major ridge lines of E PA, or near the stationary front/outflow boundary intersections across N NJ. Aloft, WV shows a very strong jet streak across the St.Lawrence River Valley with broad right entrance ascent pattern across much of the Upper OH valley through central NY into the Interior of New England. The convectively enhanced shortwave continues to shear/elongate from SSW to NNE with upstream core over E OH and into confluent flow will continue, along with the right entrance ascent provide ample DPVA and ascent profiles throughout the Mid-Atlantic. Bulk shear is greater near and north of the surface front likely to result in greater cell organization but is further distanced from deepest moisture/highest Theta-E near the Chesapeake Bay into SE PA. As such, there is likely to be difference in convective activity/manner across the area. Weak convergence along the lee trough/Blue Ridge is likely to expand areas of convection westward with time as well across NW VA. South of the Lehigh Valley, 12z guidance is increasing confidence in initial convective development through the 15-16z time frame.=20 Initial thunderstorms will be very slow moving, but have stronger/broader updrafts with 14-15Kft of warm cloud layer for highly efficient rainfall production. While inflow will be weak, it is likely to pull multiple broad columns of that 2-2.25" Total PWat air to support 2-3"/hr rates by 18z given very slow cell motions (slower further south). Storm scale interaction/cold pool generation is likely to be the dominant mode of propagation, so interactions/collisions/mergers are possible and may result in increased duration to support localized 3-4" totals.=20=20 The area remains saturated with 0-40cm soil ratios over 50-60% which is in the 70-80th percentile, combine that with proximity to large urban centers with impermeable surfaces; the shear rates are likely to overwhelm ground conditions quickly and result in flash flooding conditions; a localized considerable incident of flooding is possible as well.=20=20 Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!9hrI42RnPj-Nx2zy2ymsXzty6nsGmiRtfT7ZVpm0oTCfYV8D38S4xUxTncnvrKYWKRt1= vSKVIkfDWzFPySb8KJnlHw0$ for graphic product... ATTN...WFO...BGM...CTP...LWX...OKX...PHI... ATTN...RFC...RHA...TAR...NWC... LAT...LON 41307490 41017416 40377415 39347468 38697633=20 38307774 38117909 38497956 39087905 39647778=20 40247724 40677670 41107579=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) .