Flash Flood Guidance
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Issued by NWS
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250 AWUS01 KWNH 090725 FFGMPD NCZ000-SCZ000-GAZ000-TNZ000-KYZ000-ALZ000-MSZ000-ARZ000-091300- Mesoscale Precipitation Discussion 0247 NWS Weather Prediction Center College Park MD 324 AM EDT Thu May 09 2024 Areas affected...Tennessee River Valley into southern Appalachians and Piedmont Concerning...Heavy rainfall...Flash flooding likely Valid 090723Z - 091300Z SUMMARY...Areas of flash flooding will continue across portions of the TN valley into the southern Appalachians through sunrise and possibly extend into portions of the Carolina Piedmont. Scattered additional rainfall totals of at least 2 to 4 inches are expected across the region, falling atop saturated soils, with locally significant impacts possible. DISCUSSION...07Z radar imagery and surface observations depicted a composite outflow boundary extending from the Carolinas into northern GA and TN, where it intersected an advancing, broken line of thunderstorms in western TN. Area VAD wind plots showed 850 mb winds of 35-45 kt from the SW to the south of the outflow boundary, overrunning warm/humid air atop the rain-cooled airmass where 1000 to 2500 J/kg MUCAPE was depicted via the 06Z SPC mesoanalysis. A dual jet structure aloft present over the eastern U.S. placed the TN Valley within an upper level diffluent and divergent regime. Anomalous moisture values of 1.5 to 1.8 inches were in place across the region via GPS data and Blended TPW imagery, supporting MRMS-derived peak rainfall rates of 1-3 inches per hour and a 6-hr rainfall max of 4-7 inches over northwestern GA, ending 07Z. The NE to SW oriented broken convective line in western TN is expected to continue to progress toward the ESE over the next several hours, out ahead of a cold front moving through eastern MO/AR. Meanwhile, the southwestern flank of the forward propagating squall line tracking through the western Carolinas, is likely to train over portions of GA into SC as mean west to east steering flow aligns with the outflow boundary orientation. Continued low level overrunning of the elongated outflow boundary will continue to support training/repeating rounds of high rainfall intensity to the north of the outflow as well with rainfall rates of at least 1-2 in/hr, locally near 3 in/hr over portions of TN into northern AL/GA through the morning hours. The advancing convective line from western TN will likely track over areas of the TN Valley and far southern Appalachians providing a quick inch or so of rain, adding onto rainfall totals across the region. Expectations are for at least an additional 2-4 inches for portions of the discussion area through 13Z, though locally higher amounts cannot be ruled out. Given the prolonged duration of heavy rainfall across the region, some significant areas of flash flooding will be possible. Otto ...Please see www.wpc.ncep.noaa.gov for graphic product... ATTN...WFO...BMX...CAE...FFC...GSP...HUN...LMK...MEG...MRX... OHX... ATTN...RFC...LMRFC...OHRFC...SERFC...NWC... LAT...LON 36748565 36548461 35748302 35618162 34738097 33928118 33678274 33828457 34108639 34238968 35319013 35878838 36608691