Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Sun Jul 09 2023 05:43:05 AWUS01 KWNH 090542 FFGMPD VAZ000-NCZ000-WVZ000-OHZ000-TNZ000-KYZ000-091130- Mesoscale Precipitation Discussion 0670 NWS Weather Prediction Center College Park MD 142 AM EDT Sun Jul 09 2023 Areas affected...Ohio Valley Concerning...Heavy rainfall...Flash flooding possible Valid 090541Z - 091130Z Summary...Showers and thunderstorms developing ahead of a cold front will expand in coverage and drift across the area overnight. These slow moving storms with rainfall rates of up to 2"/hr may cause flash flooding. Discussion...The regional radar mosaic tonight depicts an expanding area of rainfall with embedded thunderstorms from central TN through southeast OH. This convection is developing ahead of a surface cold front analyzed by WPC an within the favorable diffluent RRQ of a poleward arcing jet streak clearly evident in the GOES-E WV imagery. The thermodynamic environment continues to be favorable for heavy rain noted by GPS measured PWs rising to around 1.7 inches, above the 90th percentile for the date, and MUCAPE still analyzed by the SPC RAP of 500-1000 J/kg. Although surface CINH is noted in most areas, the increased deep layer ascent through upper ventilation and downstream of a vorticity max is allowing parcels to strengthen within the elevated CAPE. Rainfall rates within thunderstorms have been estimated by KJKL to be 1-1.5"/hr, resulting in significant FLASH responses near the TN/KY border already due to slow motions. As the RRQ of the upper jet continues to overlap the surface front, and a shortwave lifts northeast within the broad synoptic troughing, forcing for ascent will remain robust overnight. This will occur in tandem with 850mb inflow from the W/SW of 15-20 kts to resupply high PWs and instability. Although the LLJ may veer more to the W overnight, this will continue to originate from a very moist column, and PWs may climb to 1.8-1.9 inches, nearing daily records. A lack of bulk shear should keep most convection to the pulse variety, and will likely be generally embedded within a more expansive moderate precipitation shield on the persistent WAA. However, generally weak steering flow noted via 0-6km mean winds of just 10 kts, and the veering LLJ, will allow the Corfidi vectors to collapse to just 0-5 kts. This will result in nearly stationary storms at times, especially in upwind terrain features. The most intense rainfall rates within convection could produce as much as 0.5"/15min according to the HRRR, which when combined with the larger shield of moderate rain could produce 2-3" of rainfall. Locally higher amounts are likely, especially within any stationary convection or where upslope flow can enhance ascent, as reflected by HREF 3"/6hrs probabilities as high as 30%. 7-day rainfall according to AHPS has been generally 100-150% of normal, compromising FFG to as low as 1.5"/3hrs in some areas. While the HREF exceedance probabilities are modest, it is likely that the heaviest rain rates, especially if they occur in sensitive terrain, will result in rapid runoff which could produce instances of flash flooding as well. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!5K8EdRksRlfCwfAI_jpyjTRyH8SAw9so9ayjWiMRNAOydD5PnQTladXBiks-HkdNx5Rs= AhSr3fTlbzhAEd6at5f0eOo$ for graphic product... ATTN...WFO...GSP...ILN...JKL...LMK...MRX...OHX...PBZ...RLX... RNK... ATTN...RFC...LMRFC...OHRFC...SERFC...NWC... LAT...LON 40018225 40018206 39838103 39378038 38828020=20 37908054 37038124 36138183 35538254 35218354=20 35268420 35528506 36068587 36708598 37508545=20 38048504 38188497 38798439 39368377 39788309=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) .