Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Jul 29 2023 17:22:33 AWUS01 KWNH 291722 FFGMPD MEZ000-MAZ000-NHZ000-RIZ000-VTZ000-CTZ000-NYZ000-PAZ000-292300- Mesoscale Precipitation Discussion 0811 NWS Weather Prediction Center College Park MD 121 PM EDT Sat Jul 29 2023 Areas affected...Southeast Upstate NY...Much of New England... Concerning...Heavy rainfall...Flash flooding likely Valid 291730Z - 292300Z SUMMARY...Risk of flash flooding expanding into New England ahead of the approaching shortwave. Heavy rainfall of 2-4" crossing fairly saturated soils, likely to induce scattered to numerous localized incidents of flash flooding through Saturday evening. DISCUSSION...Downstream of MPD 810 currently in affect across much of Upstate NY, reduced cloud cover across SE NY into New England in proximity to the west to east stationary front generally near/just north of the MA and VT/NH state boarder. Pooled deep layer moisture of 1.5-1.75" total PWATs and surface Tds in the upper 60s to low to mid 70s combined with the increased insolation has resulted in CAPEs increasing into the 1500+ J/kg range. Weaker capped environment, nearer the surface boundary with some enhanced mountain circulation convergence at the peaks of the Catskills, Green and White Mtns is starting to result in scattered Tcu ahead of the main shortwave still back across W NY. As the wave approaches, better divergence aloft combined with backing low level flow and increasing deep layer moisture flux convergence will allow for convective expansion across New England. Having greater heating, vigor of the updrafts will support further isallobaric acceleration of localized flow increasing rainfall production/efficiency for thunderstorms especially after 21z; with HRRR 15 minute rainfall totals suggest 1.25-1.5" values, indicative of this efficiency. Deep layer steering suggests 25-35kts of forward speed to limit duration of the expanding convective line, but short-term training in line segments are probable to increase duration for spots of 2-3" over a 1-2 hours.=20 Additionally, there will be cells that develop well east of the expanding linear convective band, these cells are likely be very slow moving given approach of stronger height-falls hinting at upwind propagation vectors. These more isolated spots may see 3-4" totals when all is over having the best chance of inducing flash flooding. However, the region, particularly east of the Hudson River Valley into Massachusetts and the upper Connecticut River Valley has seen recent heavy rainfall with continued saturated soil conditions in places given AHPS 7-14 day anomalies remain well above normal (200-400%). As such, flash flooding is considered likely across the area of concern with scattered to numerous incidents of flash flooding probable through the evening hours. Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6u0k8W_lLMYX1CunsSyNfxWS_28S2vWlyigne7tzYbJkaWfjzUhBoGgyhFouZFp4Ny8a= QHLn50jy2Ei1a5zmNEyD0x0$ for graphic product... ATTN...WFO...ALY...BGM...BOX...BTV...GYX...OKX... ATTN...RFC...MARFC...NERFC...NWC... LAT...LON 44796980 44256900 43177036 42277096 41587218=20 41377414 41527566 42047584 42877482 44027334=20 44647164=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) .