Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Thu Dec 28 2023 03:21:14 AWUS01 KWNH 280320 FFGMPD CTZ000-NYZ000-NJZ000-PAZ000-DEZ000-MDZ000-280930- Mesoscale Precipitation Discussion 1225 NWS Weather Prediction Center College Park MD 1019 PM EST Wed Dec 27 2023 Areas affected...Eastern MD...DE...Eastern PA...NJ...Southeast NY & NYC... Concerning...Heavy rainfall...Flash flooding likely Valid 280330Z - 280930Z SUMMARY...Prolonged moderate rainfall over saturated/dormant grounds continues to pose above normal runoff and potential for flooding, especially in urban centers. DISCUSSION...GOES-E WV suite depicts a well defined, nicely anti-cyclonically curved 130-140kt 250mb jet streak across central VA to the southern Delmarva with broad diffluence in the left exit region still remaining over the Delaware valley. EIR and WV loops note the vertical ascent pattern with north to south waves of transverse banding in this ascent region. This is critical given any minor mid-level instability has been all but exhausted over the last few hours with about 100-250 J/kg still remaining in pockets. 925 to 700mb wind profiles do show a bit of broadening/reduction of the vertical stacking of the deep confluence zone that has been pumping well above average moisture into this ascent column. 1.25-1.4" total PWats and 30-35kts of confluent flow should continue to support efficient rainfall generation even if the band is broadening a touch as it lifts through the Delaware Valley and encroaches into central NJ and SE NY/NYC. Rates up to .66"/hr continue to be observed, especially further south into SE PA and the Eastern Shore but .33-.5"/hr will continue to spread north with time. Given the prolonged nature of these rates additional 2-3" are increasingly probable from Dover to Trenton perhaps reaching NYC and eastern Long Island through the 06-09z time period. RAP/HRRR continues to suggest that strongest divergence in the left exit will reduce after 07z as mid-level inflection continues to lift northeast through the Poconos into the lower Hudson Valley. This will weaken the gradient in the low level jet and said divergence will diminish. However, the approach of the surface low near the mouth of the Chesapeake, while no-longer deepening will provide solid easterly low level flow and maintain, perhaps sharpen the FGEN ascent along the NJ coast to keep those rates (up to .5"/hr) maintained through 09z with localized totals of 1.5-3". Given recent heavy rainfall through December and dormant ground conditions, most of the rain will be runoff and likely to induce localized flooding conditions. The uncertainty is if the rates result in rapid inundation flooding or just a broad areal concern; irrespective of the rate of water rise, flooding is likely given some areas FFG values are already below 1"/3hrs across E PA, northern NJ...and therefore WPC designation will be for likely flash flooding, even if it is not traditional 'flashy' rises...impacts are likely to be noticeable especially in proximity to urban areas and prone flood zones. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!71UYMefamDDjbcg8eYhswOCYnya0Qf5eiQAenCsWU-ZpFk9-G3PGZbePhZTcyaN16R5c= exVtHNw3Yphv4Y9oYm78VZk$ for graphic product... ATTN...WFO...AKQ...CTP...LWX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 41347408 41087367 40897354 40477361 39787406=20 39267444 38657490 38137513 38007565 38017616=20 38477679 39847601 40777534 41237462=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) .