Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Oct 07 2023 14:39:45 AWUS01 KWNH 071439 FFGMPD MAZ000-CTZ000-NYZ000-NJZ000-072000- Mesoscale Precipitation Discussion 1138 NWS Weather Prediction Center College Park MD 1039 AM EDT Sat Oct 07 2023 Areas affected...Tri-State area of NJ, NY, and CT Concerning...Heavy rainfall...Flash flooding possible Valid 071437Z - 072000Z Summary...Increased training of showers and thunderstorms will lift northward into the Tri-State area this afternoon. Rainfall rates may exceed 2"/hr at times, which through training could produce 2-3" of rain with locally higher amounts. Flash flooding is possible, especially in urban areas. Discussion...The regional radar mosaic this morning shows a line of convection which has blossomed south of Long Island along a potent inverted trough angling into the Atlantic Ocean. This trough is sharpening downstream of a cold front analyzed by WPC shifting eastward towards the Mid-Atlantic coast. Additional ascent is occurring through the RRQ of a jet streak arcing into Canada, mid-level divergence downstream of the primary trough axis, and an embedded shortwave rotating through. Thermodynamics are favorable for heavy rain, with PWs measured by the 12Z KOKX sounding of 1.51 inches, above the 90th percentile according to the SPC sounding climatology, and weak moist adiabatic lapse rates through a deep warm cloud depth of around 11,000 ft. This is supporting efficient warm rain processes, with radar-estimated rain rates reaching 1.5-2"/hr south of Long Island. The recent 12Z high-res model runs are performing quite well this morning, so there is moderate to high confidence in the evolution through the aftn. As the front approaches from the west and synoptic ascent remains robust, convection should continue to develop and expand along this inverted trough within the impressive thermodynamics. Eventually, convection ahead of the front may merge with storms along the inverted trough which will finally progress things eastward, but until that time it is likely training of cells from S to N will occur. These cells will likely have rain rates eclipsing 2"/hr as shown by HREF neighborhood probabilities, with HRRR 15-min rainfall reaching 0.5 to 0.75 inches in some areas. Training of these cells is will occur through boundary-parallel 0-6km mean winds, with additional backbuilding possible as convergence along the inverted trough drives regeneration into the favorable thermodynamics. Where the most intense training occurs, heavy rainfall axes of 2-3" are likely, with locally up to 5" possible as reflected by the HREF exceedance probabilities. This region has been exceptionally wet the past 14-days, with AHPS rainfall departures 300-600% of normal driving saturated soils and compromised FFG as low as 0.75-1"/1hr and 1.5-2.5"/3hrs. There may not be a perfect overlap of the heaviest rainfall (which may stay just east of NYC) and the lowest FFG (whch is just west of the city), but the vulnerability of this entire region suggests an enhanced flash flood potential due to training. Still, instances of flash flooding should generally be isolated, and confined to where training occurs over the most vulnerable soils. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8T3v1_xkZgRjZTPQ2C4NTftLmjDvjngGaWaK32AYOE3CWHaIjFElu6WgDWcWwkOp8l01= 57WbCAvysJ84mFigrxi6S0c$ for graphic product... ATTN...WFO...ALY...BOX...OKX...PHI... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 42117323 41897294 41627282 41267285 40897286=20 40727295 40627332 40497368 40217391 39877404=20 40097451 40737476 41107469 41487422 41747377=20 42037348=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) .