Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Mon Jul 22 2024 06:00:09 AWUS01 KWNH 220600 FFGMPD VAZ000-TNZ000-KYZ000-INZ000-221200- Mesoscale Precipitation Discussion 0689 NWS Weather Prediction Center College Park MD 159 AM EDT Mon Jul 22 2024 Areas affected...Northern Tennessee and much of Kentucky Concerning...Heavy rainfall...Flash flooding possible Valid 220600Z - 221200Z Summary...Showers and thunderstorms will regenerate along a convergence boundary and move slowly through the overnight hours. Rainfall rates may exceed 2"/hr at times, leading to 2-3" of rain with locally higher amounts. Flash flooding is possible. Discussion...The regional radar mosaic late tonight shows an expansion of thunderstorms across portions of northern TN and into southern KY. This convection is developing along a convergent boundary that appears to be a remnant outflow boundary (OFB) from earlier Sunday's convection, and downstream of a shortwave moving out of northern MS/western TN. Forcing for ascent is also being provided through the RRQ of an upper jet streak lifting into the Mid-Atlantic, while locally backed 850mb flow noted in VWPs and via the SPC RAP analysis is converging into the region. This LLJ, although modest at just 10-15 kts, is drawing elevated PWs of 1.75-1.9 inches and MLCAPE of 1000 J/kg northward to support heavy rainfall, and recent radar-estimated rain rates have eclipsed 1.5"/hr on the northern edge of the accompanying theta-e ridge. The recent runs of the HRRR have been playing catch up to the current activity noted on radar, but currently is initializing quite well, and appears to be the most reasonable solution of the available CAMs. This indicates that convection will continue to develop overnight, especially along this convergence axis and downstream of the shortwave where ascent will be maximized in the favorable thermodynamic environment. HREF neighborhood probabilities for 1"/hr (2"/hr) rainfall rates reach 40% (10%), and storm motions could effectively be near zero at times along this boundary. Since many of the CAMs outside of the HRRR are struggling with the current activity, the HREF probabilities of just 10-15% for 3"/6hrs are probably a bit low, and where these intense rates drift along the boundary, rainfall could exceed 3" in places, especially from north of Nashville, TN and into the Pennyroyal Plateau. Additional convective development is possible anywhere in the discussion area as forcing and thermodynamics align, and repeating rounds of thunderstorms are possible, but the heaviest rainfall should occur along this remnant OFB. FFG is compromised across much of this region, falling to as low as 2"/3hrs in central KY, and just 1-1.5"/3hrs in eastern KY. This is due to 7-day rainfall that according to AHPS has been more than 150% of normal in many areas, leading to soils that are more sensitive to runoff and flash flooding. Although HREF FFG exceedance probabilities are modest, due at least in part to the non-HRRR CAMs struggling, it is possible that any slow moving or repeating storms with heavy rainfall could cause instances of flash flooding through the early morning. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!94apY-sAbTG2u48sRss6Z1L99OQ0JG2_Pp2vg522wv17jtAN5ncoU6rtx4vm8n2WVbP8= FEMfgMEjjTW9snanWRaCLKo$ for graphic product... ATTN...WFO...JKL...LMK...MEG...MRX...OHX...PAH...RLX... ATTN...RFC...LMRFC...OHRFC...NWC... LAT...LON 38128466 38058328 37888265 37628235 37018262=20 36588381 36308501 36068602 35978694 35988771=20 36138834 36708857 37238813 37638747 37998629=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 3.20-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .