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