Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Fri Aug 04 2023 16:20:35 AWUS01 KWNH 041620 FFGMPD MEZ000-MAZ000-NHZ000-VTZ000-NYZ000-PAZ000-042230- Mesoscale Precipitation Discussion 0859 NWS Weather Prediction Center College Park MD 1220 PM EDT Fri Aug 04 2023 Areas affected...Upstate New York, Central New England Concerning...Heavy rainfall...Flash flooding possible Valid 041630Z - 042230Z Summary...Showers and thunderstorms will expand in coverage this afternoon and move eastward from Upstate NY through New England. Rainfall rates at times will likely exceed 1"/hr, which through training could produce 1-3" of rain. Flash flooding is possible. Discussion...The regional radar mosaic this aftn indicates increasing coverage of showers and thunderstorms from central Upstate NY through central New England. This convection is blossoming in response to increasing deep layer ascent due to an overlap of low-level convergence ahead of a cold front, modest height falls within a broad mid-level trough, and increasing upper diffluence in the LFQ of a jet streak swinging south of the region. This lift is occurring into favorable thermodynamics characterized by PWs of 1.25-1.5 inches as measured by GPS, and increasing SBCAPE as high as 2000 J/kg as analyzed by the SPC RAP. Convection within this environment is producing radar-estimated rain rates around 0.5"/hr, and these rates will likely intensify through the aftn. As the cold front pushes eastward, deep layer ascent will increase across the region, aided by even more favorable positioning of the upper jet streak to enhance cyclonic diffluence. This will occur in tandem with the most robust thermodynamics, as aftn heating surges instability concurrently with SREF low-level moisture flux peaking above +1 sigma. This should drive an expansion of convective coverage which is shown in most available high-res simulated reflectivity. Additionally, rainfall intensity should increase which is reflected by HREF 1-hr neighborhood rain rate probabilities peaking this evening, coincident with HRRR 15-min rainfall showing pockets of 0.5-0.75". 0-6km mean winds will remain rapid at 20-25 kts, suggesting cells will be progressive this aftn, which will somewhat limit the flash flood risk. However, flow will generally be parallel to the front indicating the likelihood of some training to drive multiple rounds of convection in some areas. This could offset the progressive motion, and this is reflected by HREF 6-hr rainfall probabilities suggesting a low-end potential for 3 inches, which is matched by the 6-hr LPMM from the experimental RRFS TL ensemble. This area remains primed to rapid runoff due to still saturated soils from 30-day rainfall that has been 150-300% of normal, resulting in still climatologically exceptional USGS streamflow anomalies and compromised FFG. The HREF exceedance probabilities reach as high as 60% over these most vulnerable soils. While progressive storm motions should generally keep the flash flood risk isolated, any short term training of heavier rain rates, especially atop the most sensitive soils, could produce flash flooding today. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6iPC2c6YkhKFbLKuzhGXyIEV__RiQ-GV80DjHZ4Dn9dt5HLyc_TLHDuRtyBNSOq4_BOC= azbsT22TLhBZR6boNOA0N6Q$ for graphic product... ATTN...WFO...ALY...BGM...BOX...BTV...BUF...GYX... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 45127081 45036996 44486975 43996990 43417039=20 42887112 42407219 42037361 41727520 41847598=20 42387621 43237563 44357496 44997383 45047244=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) .