070
AWUS01 KWNH 251501
FFGMPD
VAZ000-NCZ000-GAZ000-TNZ000-KYZ000-ALZ000-252100-

Mesoscale Precipitation Discussion 1053
NWS Weather Prediction Center College Park MD
1101 AM EDT Wed Sep 25 2024

Areas affected...Southern Appalachians

Concerning...Heavy rainfall...Flash flooding likely

Valid 251500Z - 252100Z

SUMMARY...Flash flooding will be possible this afternoon as the
Predecessor Rain Event (PRE) begins from northeast Alabama through
the Southern Appalachians

DISCUSSION...The well-advertised PRE has begin to take shape
across portions of the Southeast this morning. Storms have
developed in a cluster across eastern Alabama with another one
over eastern Tennessee. FFGs in the area are high...generally
around 2.5 inches in 1 hour for Alabama and Georgia, but they are
much lower in eastern Tennessee around Knoxville.

An upper level low across far western Tennessee is drawing
increasing moisture northwestward across Georgia into this zone
where the storms are forming. Upper level jet stream winds are
expected to approach 100 kts, which will increase the upper level
divergence over the storms in the right entrance region, thus
further enhancing the lift.

Through mid-afternoon, CAMs guidance suggests additional line
segments of storms will develop generally aligned SSW to NNE
across the area. Embedded cells within the lines, as now, will
track NNE, roughly parallel to the lines. The result will be some
areas seeing multiple rounds of training thunderstorms, each
capable of producing rainfall rates to 2.5 inches per hour...with
those heaviest rates more likely once the storms move more into
Georgia later this afternoon. Further, since the storms will be
moving roughly parallel to the lines, the lines` forward speed to
the east will be slow, allowing for multiple cells repeating over
the same areas. Even now with pockets of 2 inch per hour rates
associated with the strongest storms, the training nature of the
storms will result in multiple rounds over potentially flood-prone
and urban areas. Thus, even where FFG values are higher, the
repeating nature of the storms will locally lower values as
repeated storms move overhead.

Wegman

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...BMX...FFC...GSP...HUN...JKL...MRX...

ATTN...RFC...LMRFC...OHRFC...SERFC...NWC...

LAT...LON   36768370 36298236 34918356 33728479 32768559
            33518664 34718567 35388522