Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue May 20 2025 21:32:02 AWUS01 KWNH 202131 FFGMPD TNZ000-KYZ000-210200- Mesoscale Precipitation Discussion 0297 NWS Weather Prediction Center College Park MD 530 PM EDT Tue May 20 2025 Areas affected...portions of central and northern West/Middle TN into western and central KY Concerning...Heavy rainfall...Flash flooding possible Valid 202130Z - 210200Z Summary...Training and repeating of 1-2"/hr rates may lead to localized totals of 2-3" (much of which will occur over relatively saturated soils) through 9PM CDT. Scattered instances of flash flooding are possible. Discussion...Semi-discrete severe thunderstorms are rapidly organizing linearly near (and just east) of the MS River (along the TN/AR/MO/KY border). This is occurring within a deeply unstable (2000-3500 J/kg of SBCAPE) warm sector, with the clearing cold front lagging significantly behind the line of storms (across eastern AR/southwest MO). Precipitable water along and ahead of the storms is between 1.5-1.9 inches, between the 90th percentile and record levels for the Nashville area (per BNA sounding climatology), and moderate to strong low-level moisture transport will transport these highly anomalous values northeast into the MPD region (with 925-850 mb flow of 35-45 kts). A semi-phased jet stream is providing sufficient diffluence aloft (though not ideal, within the right exit region of the broad jet streak), and ample deep layer (0-6 km) shear (50-60 kts) to organize updrafts into supercell structures (which are occurring both along and out ahead of the main line). The primary concern going forward with regard to flash flooding are for continued proliferation of convection to result in training and repeating elements along and out ahead of the main line. Notably, Flash Flood Guidance (FFG) across northern Middle TN into south-central KY is much lower than surrounding areas (1.5-2.0" over 3-hr), and this may contribute higher coverage (and greater potential for locally significant) flash flooding. MRMS QPE CREST unit streamflow indicates somewhat elevated activity in this region already, as NSSL QPE estimates 1.0-2.0" totals over the past 6 hours from an earlier line of storms. Hi-res guidance is in relatively good agreement with QPF through 02z (9pm CDT), depicting localized 2-3" totals over the next 3-5 hours (per 18z HREF and experimental 12z RRFSe PMM QPF, as well as the 90th percentile accumulated rainfall of the 19z and 20z runs of the experimental WoFS). Given the aforementioned wet antecedent conditions, this suggests 20-40% chances for FFG exceedance (per 40-km neighborhood method of the 18z HREF and 12z RRFSe ensembles). Scattered instances of flash flooding are possible. Churchill ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!8KWYKChrGYjFMQVCsaqcrvSchhLS26ylgXMWZGbkzN0RVLwRgXU0BUhj6twJC6K0zEPA= Etc7X1uyHR7i8fsGmDu_unI$ for graphic product... ATTN...WFO...LMK...MEG...OHX...PAH... ATTN...RFC...ORN...TIR...NWC... LAT...LON 37778649 37698540 37138513 36348524 36038574=20 35758687 35338956 35958899 36528856 37148819=20 37488745=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) .