Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sat Sep 09 2023 17:31:47 AWUS01 KWNH 091731 FFGMPD NYZ000-PAZ000-092300- Mesoscale Precipitation Discussion 1044 NWS Weather Prediction Center College Park MD 131 PM EDT Sat Sep 09 2023 Areas affected...Central PA...South-Central NY... Concerning...Heavy rainfall...Flash flooding likely Valid 091730Z - 092300Z SUMMARY...Training thunderstorms along/ahead of compact shortwave may result in spots of 2-4". Localized flash flooding becoming possible through this afternoon. DISCUSSION...Regional RADAR mosaic and visible imagery show a compact shortwave across NE PA, starting to lift northeast. WV suite and GOES AMVs denote the shortwave should remain intact within the right entrance of the 35-45kt 3H jet but also the approaching left exit of a 50kt speed max crossing NoVA. Strong southerly low to mid-level flow (20-35kts per RAP/VWP at CCX) will enhance moisture flux into the well defined boundaries associated with the shortwave, particularly across N PA into S NY where orientation is nearly orthogonal. Moisture values will increase from 1.5 to 1.75" to increase rainfall efficiency. Skies are fairly clear across PA to allow for peak insolation but may be a bit more limited nearer the boundary where clouds have limited heating, but 1500-2500 J/kg of CAPE will be available for strong updrafts with the best moisture convergence. This is already starting to manifest with the weak moisture confluence along the trailing convergence trof/effective cold front of the shortwave. This aligns with northward Laurel Hill ridge line into the Allegheny Mountains, so some mountain circulation may be aiding this development. Given the focused low level flow, backbuilding and redevelopment is probable along the ridge while deep layer steering should support some short-term training.=20 Stronger rain rates up to 2" are likely with the stronger flow nearer the shortwave/effective triple point in flow across N central PA. 500-1000mb thickness does suggest slow eastward propagation of this effective boundary to enhance at least short-term training/repeating is possible. As such, spots of 2-3" are consistent within the 12z Hi-Res CAM suite, with HRRR trends suggesting a spot 4" total is not out of the realm of possibility by late evening.=20 While much of central PA has higher FFG, parts of the Allegheny Mtns and upper reaches of the Susquehanna Valley have natural lower FFG of 1.5-2"/hr or 2-3"/3hrs, and generally match up with the strongest signal in the guidance, suggesting localized flash flooding is likely particularly after peak heating when rain-rates are greatest (after 20-21z). Gallina ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6oxhUJA09MO9OBuAyLD1wRFrbKOsQAF2rsALUkbi0-CgvzUk9aACsJ6T_iLdFMpq5CSv= A5_VBsviWK4DX_RGPneoZqI$ for graphic product... ATTN...WFO...BGM...BUF...CTP... ATTN...RFC...MARFC...NERFC...OHRFC...NWC... LAT...LON 42817628 42417542 40887643 40297700 39787764=20 39727832 39757893 40027914 40327895 41017864=20 41467853 42197825 42697770=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) .