Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Apr 30 2023 20:21:14 AWUS01 KWNH 302021 FFGMPD CTZ000-NYZ000-NJZ000-PAZ000-010219- Mesoscale Precipitation Discussion 0219 NWS Weather Prediction Center College Park MD 420 PM EDT Sun Apr 30 2023 Areas affected...northern half of NJ & southeastern mainland NY Concerning...Heavy rainfall...Flash flooding possible Valid 302019Z - 010219Z Summary...A couple rounds of convection are expected to lead to heavy rains across northern NJ and southeastern NY. Hourly rain totals to 2" with local amounts to 3" are possible, which could lead to flash flooding. Discussion...A couple rounds of thunderstorms -- one moving across southern NJ and another in southeast VA -- are moving towards the region from the south-southwest. MU CAPE is 500+ J/kg across southern NJ, associated with the northward movement of a coastal warm front to the north of a low pressure system over Chesapeake Bay. Divergence aloft is increasing as an upper low/trough across NC takes on a negative tilt. Precipitable water values are 1.15-1.3" and rising per GPS data. Effective bulk shear of 30-40 knots is being mainly driven by southerly flow of 35 kts at 850 hPa (per VAD wind profiles) overriding east 10-15 knots of surface wind. RAP guidance suggests that 500-1000 J/kg of MU CAPE should move as far poleward as southeast NY as the surface low moves generally up the Fall Line and Delaware River Valley with time. This should allow a couple rounds of convection to move into the region -- one early and one late in the period. As precipitable water values rise towards 1.5" this evening, hourly rain totals could reach 2" should any thunderstorms train, evolve into mesocyclones, or merge which would overwhelm the low flash flood guidance values in and near central and northern NJ and possibly broach them across southeast mainland NY. The mesoscale guidance suggests that 2" should be the high bar for amounts, though local 3" amounts over the next six hours can't be ruled out, which would be most problematic over saturating soils and urban areas. There are expected to be a mix of short and long duration heavy rain issues during the MPD period, with any flash flooding occurrences expected to be isolated to widely scattered.=20 Roth ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7pQoZMFZqW65UVgVwOQnVFhmhGOGiP5qWenp3NNTXO0QOIDzBzD_OoecdTdC5uKvi8Lh= 39Aau1c-KZYvmNPOhPp25C0$ for graphic product... ATTN...WFO...ALY...BGM...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 42197408 41627361 41077365 40817396 40507401=20 40217397 39907409 40127458 39877549 40667515=20 41047503 41597480=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) .