Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jul 09 2023 16:16:45 AWUS01 KWNH 091616 FFGMPD CTZ000-NYZ000-NJZ000-092119- Mesoscale Precipitation Discussion 0675 NWS Weather Prediction Center College Park MD 1214 PM EDT Sun Jul 09 2023 Areas affected...Southern NY...Southwest CT...Central NJ...Greater NYC Metro Concerning...Heavy rainfall...Flash flooding likely Valid 091614Z - 092119Z SUMMARY...A developing convergence zone stretching from the Lower Hudson Valley to central NJ will likely trigger strong storms containing torrential downpours. Flash flooding is likely this afternoon. DISCUSSION...As thunderstorm activity continues to blossom on the northern and western periphery of NYC, temperatures will cool and allow for a stronger differential heating gradient to setup from central NJ to western CT. It it clear there is no shortage of instability and moisture for storms to work with. RAP mesoanalysis shows MLCAPE has already risen to >1,500 J/kg, and as the southerly 850mb moisture transport picks up this afternoon, PWATs will rise to above 2.0". RAP forecast soundings at KLGA around 21Z showed >90% low-mid level RH values, PWATs above 2", warm cloud layers >12,000 feet, and with sfc-900mb winds out of the southeast, a more veered profile. These profiles suggest these storms will have no problem supporting efficient warm rain processes. The question becomes the triggering mechanism, especially in NYC and central NJ. North of the NYC metro, there is higher elevation to work with that southerly upslope flow will be enough to initiate more thunderstorm activity. Closer to NYC, the expectation is that as the storms over eastern PA and the Lower Hudson Valley congeal this afternoon, a tightening of the thermal/CAPE gradient will ensue. The latest RAP shows this potential well, highlighting an area of deep layer moisture flux convergence setting up overhead around 21Z. There is also the potential for outflow boundaries to propagate toward the city and act as a trigger, as well as any sea breeze activity over NJ that tracks northward due to SSW 850-500mb winds aloft. The biggest takeaway is these storms will have the potential to generate 2-3"/hr rainfall rates with the more heavily urbanized corridor particularly susceptible to flash flooding. The cities north of NYC (White Plains on north) have a greater potential to see flash flooding given their better position with higher elevation and enhanced upslope flow. The flash flood threat will increase around NYC by mid-afternoon. Flash flooding is most likely to occur in low-lying areas and poor drainage areas on roadways. Mullinax ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5gzaggOSYRiKKX_zpCGd1i7BBlWWEutLX6zAT7EGvtvTyRrByyxO3RgJPXTJQpHdcmSw= GbNT_Q0wdAvzFC6pY5VtzxY$ for graphic product... ATTN...WFO...ALY...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 41737338 41657305 41257312 40847358 40317389=20 40127404 40377443 41157383 41717366=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) .