Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 17 2023 18:03:07 AWUS01 KWNH 171803 FFGMPD PAZ000-MDZ000-VAZ000-WVZ000-OHZ000-KYZ000-INZ000-180000- Mesoscale Precipitation Discussion 0753 NWS Weather Prediction Center College Park MD 202 PM EDT Mon Jul 17 2023 Areas affected...Central and Eastern Ohio Valley Concerning...Heavy rainfall...Flash flooding possible Valid 171800Z - 180000Z Summary...Showers and thunderstorms developing ahead of a cold front will increase and coverage and train to the east through this evening. Rainfall rates of 1-2"/hr are likely, resulting in 1-3" of rainfall. Flash flooding is possible. Discussion...The regional radar mosaic this afternoon shows rapidly expanding coverage of showers and thunderstorms from eastern KY and southern OH through western PA and much of WV. This convection is developing within modest height falls downstream of a pronounced mid-level trough axis shifting eastward, aided by an embedded shortwave noted in the RAP analysis and GOES-E WV imagery. Additionally, a poleward arcing jet streak over New England is leaving its diffluent RRQ atop the Ohio Valley, providing an additional mechanism for ascent. This deep layer lift is occurring within favorable thermodynamics for heavy rainfall characterized by PWs of around 1.3 inches as measured by GPS, around the 75th percentile for the date, and SBCAPE of 2000-3000 J/kg. Rainfall within this fresh convection is already reaching radar-estimated rates of 1-1.5"/hr, with continued intensification likely into the evening. As the shortwave lifts northeast in tandem with increasing height falls and continued upper diffluence, convection should become more widespread as reflected by the available high-res guidance. This is due not only to the increasing deep layer ascent, but more robust thermodynamics as PWs surge above 1.5" in conjunction with a ribbon of SBCAPE arcing from the SW to above 3000 J/kg. Within this environment, convection will have the capability to produce rainfall rates above 2"/hr as noted by modest HREF probabilities, with 15-min rainfall from the HRR guidance possibly exceeding 0.5" in some areas. General W/SW flow through the 0-6km layer noted in regional 12Z U/A soundings will drive mean storm motions to 15-25 kts, but this speed will be somewhat offset by aligned Corfidi vectors which will also be parallel to a pre-frontal trough. This could result in short term training in many areas, with some backbuilding into the greater instability also possible by this evening. Where the longest duration of training can occur, or along axes where multiple rounds of convection track, rainfall of 1-3" is likely. 7-day rainfall across this regio has been above normal noted by pockets of 150-300% of normal according to AHPS. This has resulted in more sensitive soils and lowered FFG to just 1.5"/3hrs in some areas. Although HREF exceedance probabilities for this FFG peak around 20%, it is possible training atop these vulnerable soils, especially where within more sensitive terrain features, could result in rapid runoff and instances of flash flooding. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!72Fy2QtQMJINp3RHsgEzQ3mBRlO88BceZswcwpfunKWgs63AqU7mRqL2t9CABWMBBPW9= pBYamm1h4TzZTKEeLl0rGUk$ for graphic product... ATTN...WFO...CLE...CTP...ILN...JKL...LMK...LWX...PBZ...RLX... RNK... ATTN...RFC...MARFC...OHRFC...NWC... LAT...LON 41657941 41537872 41107824 40697827 39957843=20 39157904 38347987 37718119 37638234 37918337=20 38648434 39188489 39528478 39828392 40388265=20 41078146 41398075 41628010=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) .