Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun May 04 2025 18:21:44 AWUS01 KWNH 041820 FFGMPD NYZ000-NJZ000-PAZ000-042320- Mesoscale Precipitation Discussion 0216 NWS Weather Prediction Center College Park MD 220 PM EDT Sun May 04 2025 Areas affected...Northeast PA...Northwest NJ...Southeast NY Concerning...Heavy rainfall...Flash flooding possible Valid 041820Z - 042320Z SUMMARY...Some concentrations of showers and thunderstorms are expected this afternoon across areas of northeast PA, northwest NJ and into adjacent areas of southeast NY. Persistence of locally heavy rainfall rates may be enough to cause some areas of flash flooding. DISCUSSION...The large scale pattern across the Eastern U.S. features a deep layer cyclone over the OH Valley with an occluded surface low structure and a stationary front that extends east across central to eastern PA and into southern New England. A relatively deep warm/moist conveyor belt is noted along the East Coast with an axis of 1.25 to 1.5 inch PWs oriented south to north from the Delmarva up across eastern PA and much of NJ. Cloud cover so far today has been keeping boundary layer instability limited, but there is a pool of MUCAPE values on the order of 1000 J/kg which is being aided by a southerly low-level jet of 20 to 30 kts and the broader warm advection regime along the East Coast. As it is, this coupled with convergent flow into the aforementioned frontal zone along with some orographic ascent over the higher terrain has been yielding some recent uptick and expansion of heavier shower activity. Some modest shear is noted across the region which coupled with some additional uptick in boundary layer instability should favor the potential for some additional convective expansion with some increase in thunderstorm activity. The latest CIRA-ALPW data shows rather concentrated moisture in the 850/500 mb layer and this should tend to favor greater rainfall efficiency with the convective cells that evolve this afternoon. Rainfall rates may reach as high as 1.5"/hour with the stronger convective elements and there may be some localized persistence/training of these cells that yield some rainfall totals of 2 to 4 inches. Some of the rainfall across parts of northeast PA, northwest NJ and southeast NY over the last 12 to 24 hours has at least started the process of moistening up the soil conditions somewhat despite very dry longer-term antecedent conditions. The rainfall this afternoon near especially some of the higher terrain may be enough to encourage some runoff problems with a threat for some areas of flash flooding. Orrison ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!7KOm-wGo_pfx8zDm3qfj2ktRqMErXDH34y1a5qtT_hxYPnt7351SJSgdcHuQ0bce5Jle= x8gKX-mMNmDDL_eLMAEbYbY$ for graphic product... ATTN...WFO...ALY...BGM...CTP...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 42537392 42337345 41687359 41017412 40527492=20 40667587 41187574 42197480=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .