Flash Flood Guidance
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Issued by NWS
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747 AWUS01 KWNH 232104 FFGMPD VAZ000-NCZ000-WVZ000-TNZ000-KYZ000-240215- Mesoscale Precipitation Discussion 1044 NWS Weather Prediction Center College Park MD 504 PM EDT Mon Sep 23 2024 Areas affected...eastern KY/TN into the central/southern Appalachians Concerning...Heavy rainfall...Flash flooding possible Valid 232103Z - 240215Z Summary...Isolated flash flooding will be possible across portions of eastern KY/TN into the central/southern Appalachians. Rainfall rates of 1-2 in/hr will be possible where brief training of cells occurs. Discussion...2045Z visible satellite and regional radar imagery showed scattered thunderstorms ongoing from portions of central KY/northern TN into the central/southern Appalachians. A recent increase in the coverage of storms appears to be driven by daytime heating and increased ascent ahead of an elongated vorticity maximum observed on water vapor imagery from western TN into northern MS. SPC mesoanalysis data from 20Z showed 1000-2000 J/kg MLCAPE and weakly anomalous precipitable water values of 1.5 to 1.9 inches across the region. The ongoing cells were moving with the deeper layer mean wind of 15-25 kt in a general eastward fashion. There is some concern that as the vorticity max over TN/MS continues to advance toward the northeast, increased forcing ahead of this feature will act on instability already in place to support greater coverage of cells heading through the remainder of the evening, increasing the potential for areas of brief training that could support locally higher rainfall rates of 1-2 in/hr. While this threat is expected to remain low, areas of low FFG exist ever portions of eastern KY/TN into the Appalachians with 1 to 2 inches in an hour. Outside of terrain, no significant boundaries were analyzed that are expected to have an impact on cell placement and the expectation moving forward is that cells will continue to remain somewhat disorganized and multicellular in nature, although increasing shear from the west may support some more organized cells. However, beyond ~02Z, the expectation is that diminishing instability with the loss of daytime heating will contribute to a reduction in storm coverage and a lowering of the flash flood threat. Otto ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...GSP...JKL...LMK...MRX...RLX...RNK... ATTN...RFC...LMRFC...OHRFC...SERFC...NWC... LAT...LON 37758313 37678264 37428100 37278083 36548088 36148161 35238255 35358389 35848446 36568457 37018485 37318493 37658490 37738455 37748401