Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Jul 18 2023 17:58:29 AWUS01 KWNH 181758 FFGMPD VTZ000-NYZ000-182200- Mesoscale Precipitation Discussion 0758 NWS Weather Prediction Center College Park MD 157 PM EDT Tue Jul 18 2023 Areas affected...Upstate New York, far western Vermont Concerning...Heavy rainfall...Flash flooding possible Valid 181756Z - 182200Z Summary...Showers and thunderstorms will expand in coverage this afternoon and then train to the northeast. Rainfall rates may exceed 2"/hr at times, resulting in 1-2" of rain with locally higher amounts. Flash flooding is possible. Discussion...The GOES-E WV imagery this afternoon clearly depicts a favorable setup for ascent to drive convection. A shortwave is evident lifting northward across PA while high-level cirrus racing northward indicates the presence of an intensifying jet streak arcing into Canada. At the surface, WPC analyzed a cold front moving across Lakes Erie and Ontario, with nearly unidirectional 850-300mb flow downstream into the warm sector. This flow is helping to draw SBCAPE above 1500 J/kg, and PWs of 1.3-1.5 inches, above the 75th percentile for the date according to the SPC sounding climatology, northward. The overlap of this robust synoptic ascent and favorable thermodynamics is resulting in increasing coverage of thunderstorms across Upstate New York this afternoon. During the next few hours, there is good agreement among the simulated reflectivity from the various high-res members in an expansion of convective coverage. This is reasonable based on the continued overlap of impressive ascent atop favorable thermodynamics. Some subtle enhancement in ascent due to more intense diffluence aloft and increasing convergence ahead of the cold front could strengthen convection as well, and the HREF indicates the probability of 1"/hr and 2"/hr rates reaching 40% and 15%, respectively. 0-6km mean winds will remain progressive at 20-25 kts, but will continue to be aligned to the approaching front and with the Corfidi vectors. This suggests at least short term training is possible as storms build back into the instability and track northeast within the unidirectional flow. Effective bulk shear reaching up to 30 kts could also help organize storms into multi-cell clusters, both causing brief upticks in rainfall rates but also lengthening the duration of heavy rain in some areas. Where this occurs, total rainfall could exceed 2 inches. 7-day rainfall according to AHPS has been 150-300% of normal across the eastern half of Upstate NY, but generally less than normal from the eastern shore of Lake Ontario and points west. This suggests the greater flash flood risk will be across the more saturated soils which are noted by USGS streamflows reaching above the 90th percentile and very low FFG, especially in the Catskills and Adirondacks. Where any short term training of these heavy rates occurs, flash flooding is possible, but will be most likely atop the most vulnerable soils and within sensitive terrain features. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!42vgmFjn2MDRNdCJxlTJ9DOoXS_1x-u8XkEYu-SspiAaYeE2NJFeq5y_itOBMq71zqXd= FDduc5Z2H6ZaZg4c15rvI7M$ for graphic product... ATTN...WFO...ALY...BGM...BTV...BUF... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 45307308 45067226 44797254 44367310 43567378=20 42807424 42347448 42087510 42107624 42107726=20 42337789 42757801 43237771 43467719 43687678=20 44097647 44437618 44777550 45227448=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) .