WPC Met Watch |
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Mesoscale Precipitation Discussion: #0794 (2020) |
(Issued at 801 PM EDT Thu Sep 24 2020
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MPD Selection |
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Mesoscale Precipitation Discussion 794
NWS Weather Prediction Center College Park MD
801 PM EDT Thu Sep 24 2020
Areas affected...Northern GA...Eastern TN...Western NC...Northeast
AL
Concerning...Heavy rainfall...Flash flooding possible
Valid 250000Z - 250600Z
Summary...Periods of moderate to heavy rain through 6Z may lead to
some minor instances of flooding for portions of the southern
Appalachians, especially for locations that have a couple of hours
of steady 1 inch hourly rainfall rates.
Discussion...A corridor of enhanced moisture convergence to the
northeast of Post-Tropical Cyclone Beta is leading to widespread
moderate to heavy rainfall with some embedded thunderstorms. This
is being confirmed by regional Doppler radars from northeast
Alabama to east-central Tennessee. This is being fueled by a
30-40 mph low level jet advecting PWs to near 1.75 inches, and
isentropic lift over a warm front across northern Georgia is
providing lift along with upper level difluence from the right
entrance region of the 250 mb jet. Furthermore, the veering
surface to 850 mb flow is mainly orthogonal to the terrain of the
southern Appalachians and resulting in orographic ascent. A
mitigating factor here is the relative lack of instability, with
much of that residing south of the warm front. Therefore, hourly
rainfall rates should generally be in the 0.5 to 1.5 inch range at
the peak of the event late this evening.
The latest suite of CAM guidance is suggesting the potential for
rainfall totals of 1 to 3 inches through 6Z, with isolated higher
totals of 4 inches possible. Based on current radar trends, it
appears the experimental HRRR, NMMB, and ARW are closest to the
depiction and expected evolution over the next several hours.
Flash flood guidance values are lowest over the northern portion
of the outlook area across northeast Tennessee, and therefore
slightly more vulnerable to flooding from heavy rainfall.
Hamrick
ATTN...WFO...BMX...FFC...GSP...HUN...MRX...OHX...
ATTN...RFC...LMRFC...OHRFC...SERFC...NWC...
LAT...LON 36528289 36318199 35668197 35178262 34808332
34438431 34278500 34228560 34348606 34678641
35328614 35858535 36208431
Last Updated: 801 PM EDT Thu Sep 24 2020
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