Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat May 20 2023 15:53:05 AWUS01 KWNH 201553 FFGMPD CTZ000-NYZ000-NJZ000-202200- Mesoscale Precipitation Discussion 0318 NWS Weather Prediction Center College Park MD 1152 AM EDT Sat May 20 2023 Areas affected...Eastern NJ...Western CT...Southern Upstate NY, NYC & Western Long Island Concerning...Heavy rainfall...Flash flooding possible Valid 201600Z - 202200Z SUMMARY...Prolonged moderate rain dotted with embedded stronger cores with up to 1"/hr rates may allow for low-end inundation flooding in prone/urban locations.=20 DISCUSSION...Loading nose of sub-tropical moisture plume off the Gulf stream is lifting north along a sharp fairly deep layer inverted trough that parallels the Mid-Atlantic Coast. Initial band along the leading nose produced .5-.75" along central LI and is starting to shift into CT starting to prep the drier ground conditions across the area. RAP analysis denotes pooling of higher most unstable air mass along the DEL/NJ coast with 100-200 J/kg of MUCAPE which is not particularly impressive at this time; however, the deep layer atmospheric river is fairly unidirectional from 925 through 500mb allowing for a favorable training environment through the remainder of the morning into the afternoon. Slightly backed surface flow is 20-25kts from the SSE and with sharp trough, not only provides strong speed convergence but also nearly 90 to 120 degrees of directional shear to overcome the weak buoyancy with the region. As such, a band of enhanced showers is expected to align favorably with the E coast of NJ angled toward NYC and the Lower Hudson Valley for the next 3-4 hours. Total PWats to 1.5" and the ascent should allow for ..25-.5"/hr rates and any weak updrafts that can tap weak instability could result in localized higher rates. This should allow for band of 1-1.5" over the next 3-4 hours. Toward 19-20z, the influence of the stronger closed upper low over the Great Lakes and approaching cold front will start enhance upper-level flow and strengthen low level jet into the 40-45kt range; this will strengthen theta-E and instability flux with some hints of 400-500 J/kg of SBCAPE filtering toward the NJ coast.=20 With better divergence aloft and higher instability, a few cores may perk up with up to 1"/hr rates with some of the reliable Hi-Res CAMs timing this intensification in proximity to the Northern Jersey shore into NYC metro area and just offshore of Delaware. However, with this favorable DPVA/divergence aloft, the ideal training environment will diminish and allow for eastward propagation of the convergence axis. It may be slow enough at first to allow for streaks of 2", perhaps an isolated 2"+ total across NYC to SW CT. This will be the best opportunity for rapid inundation flooding mainly in prone/urban locations where drainage is poor, but magnitude of flooding should be relatively low. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!79owkGr4rVR8HeLw1dWQgD4WL2BUyz98qe6gARS6qzGzxnq75P3ckzwyf8PggeFYN71D= b56GGrbq48HWLgdCX5LIea8$ for graphic product... ATTN...WFO...ALY...BOX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 41937331 41927288 41727248 41227272 40747314=20 40437377 39627408 38957471 39067503 40017449=20 40657452 41087432 41387415 41547383 41807359=20 =20=20=20=20=20=20=20=20=20=20=20=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) .