####018002707#### AWUS01 KWNH 081422 FFGMPD VAZ000-TNZ000-KYZ000-ILZ000-MOZ000-082020- Mesoscale Precipitation Discussion 0239 NWS Weather Prediction Center College Park MD 1022 AM EDT Wed May 08 2024 Areas affected...TN/KY/VA border region Concerning...Heavy rainfall...Flash flooding likely Valid 081420Z - 082020Z Summary...Scattered to numerous instances of flash flooding are likely into the afternoon with additional 2-3" of rainfall expected locally. Some flash flooding may be significant. Discussion...Heavy showers and thunderstorms are ongoing across the TN/KY/VA border region this morning, resulting in localized totals of up to 2-3" over the past several hours (per MRMS estimates). This heavy rainfall has occurred after a period of convective organization along a west-to-east oriented outflow boundary from prior convection overnight. This is occurring within a broad warm sector stretching across most of the eastern CONUS, and the mesoscale environment is characterized by an ML CAPE gradient of 1000-2500 J/kg, PWATs of 1.0-1.7 inches (near the 90th percentile, per SPC sounding climatology), and deep layer shear of 40-60 kts. Hi-res CAMs may have had the right idea, but have been far too slow based on the trends with the activity this morning. This is likely related to how defined of a forcing mechanism the outflow boundary became, and how the CAMs have struggled to depict this key mesoscale feature. The HRRR (as usual) does a bit better with this depiction given the hourly refresh cycle, and this would suggest that an additional 2-3" of rainfall are possible through 20z. Unfortunately most of this heavy rainfall will occur over much of the same areas, given the west-to-east movement along the boundary with the greatest total atmospheric moisture (and low-level transport) in western KY and northern Middle TN. While this suggests scattered to numerous instances of flash flooding are likely (given 3-hr FFGs averaging only 1.5" or so), there may also be localized instances of significant flash flooding. In addition, heavy rainfall looks to continue across much of this same region well late into the evening and overnight, so flash flooding may become more widespread (and severe) heading into the evening (and will likely necessitate subsequent discussions). Churchill ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...JKL...LMK...MEG...MRX...OHX...PAH...RLX...RNK... ATTN...RFC...LMRFC...OHRFC...NWC... LAT...LON 37428833 37288668 37068453 37298211 36868167 35908302 35898539 36118752 36488917 37128912 ####018000737#### PENA01 KWNH 081200 @UHPISF000CN MPDSUM@V2.0@0101700060@12080524@@0NMCGPHMPD %P@!' `' ` @ & B7)p&PNAM02@@An}}~~~~~~~}{||{z{{|@@n@@n@@0239 @@d&MESOSCALE DISCUSSION SUMMARY GRAPHIC @@d& OF ALL VALID MESOSCALE DISCUSSIONS AT @@d& TIME OF PRODUCT CREATION:@@d& ISSUED 05/08/2024 1422Z @@ dNOAA/NWS/NCEP@@d WEATHER PREDICTION CENTER @@d FOR COLOR VERSION SEE: @@d WWW.WPC.NCEP.NOAA.GOV @