Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Sep 10 2023 22:42:38 AWUS01 KWNH 102242 FFGMPD MAZ000-CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-110400- Mesoscale Precipitation Discussion 1055 NWS Weather Prediction Center College Park MD 641 PM EDT Sun Sep 10 2023 Areas affected...eastern Mid-Atlantic states into southern Upstate New York Concerning...Heavy rainfall...Flash flooding possible Valid 102239Z - 110400Z Summary...Showers and thunderstorms increasing across the coastal Mid-Atlantic states will train northward through the evening. Rainfall rates in excess of 2"/hr at times are likely, which could produce 2-4" of rain. Flash flooding is possible. Discussion...The regional radar mosaic this afternoon shows rapidly developing thunderstorms from northeast MD through northern NJ. This convection is expanding and intensifying in response to increasing ascent downstream of a shortwave ejecting from northern VA, and along a sharp 850mb convergence axis noted in the SPC RAP analysis draped NE to SW just inland from the coast. A positively tilted longwave trough axis continues to pivot east across the Appalachians, driving modest downstream height falls, while a modest 60-70kt jet streak lifting out of the Carolinas places favorable LFQ diffluence for ascent over the Mid-Atlantic. This overlap of favorable lift is acting upon robust thermodynamics characterized by PWs of 1.75-2.0 inches, and SBCAPE of 1000-2000 J/kg. Regional soundings indicate a deeply saturated column with weak moist-adiabatic lapse rates, which will continue to foster efficient warm rain processes into tonight. Storms blossoming from eastern VA through NJ will likely continue to expand in coverage in response to the impressive ascent, and this is reflected by simulated reflectivity in the available high-res guidance. Additionally, rainfall rates are forecast to intensify through the evening, reaching 15-25% for 2"/hr (HREF) and 0.5-0.75" in the HRRR 15-min product (brief 3"/hr rates). This convection will likely continue to lift north/northeast on 0-6km mean winds around 15 kts, with at least some organization into clusters possible within 0-6km bulk shear of 20-25 kts. Any organization could result in briefly heavier rain rates or a longer duration of this heavy rainfall. However, the area of most concern is likely to be where SE flow from the Atlantic merges into this 850mb axis, driving more intense ascent and regeneration/backbuilding within the greatest pool of instability. This feature is progged to pivot northward only slowly, and the HREF exceedance probabilities for 3" rise to 40%, with even some 10-15% probabilities for 5" in the next 6 hours forecast. Any of these impressive rain rates could result in rapid runoff and flash flooding as they move atop highly urbanized areas or sensitive soils with FFG compromised to as low as 0.75"/1hr and 1"/3hrs. While the high-res is struggling with the placement of the current activity on radar, the greatest risk for this heavy rain axis and subsequent potential flash flooding appears to be across far eastern PA into northern NJ. However, any location that receives training of these intense rain rates, especially atop less permeable surfaces, could experience instances of flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5eeqIrfi9JDCFxKZxQIZr-CS6BfR85lNk9-urYwGhFb5ZxJvJt4y7FpwTgwo8aaG9age= LgcKrpXYfIRKEluY29Micbo$ for graphic product... ATTN...WFO...AKQ...ALY...BGM...CTP...LWX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 42927464 42857349 42517333 42267326 41517338=20 41427341 40737372 39927421 39217463 38637499=20 38467549 38547585 39117636 39597669 40147649=20 41707558=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) .