WPC Met Watch |
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Mesoscale Precipitation Discussion: #0259 (2022) |
(Issued at 541 PM EDT Thu May 26 2022
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MPD Selection |
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Mesoscale Precipitation Discussion 0259
NWS Weather Prediction Center College Park MD
541 PM EDT Thu May 26 2022
Areas affected...Southern Appalachians
Concerning...Heavy rainfall...Flash flooding possible
Valid 262140Z - 270330Z
Summary...Showers and thunderstorms will continue to increase in
coverage across the Southeast and lift northward into the Southern
Appalachians this evening. Rainfall rates will likely exceed 1"/hr
at times, which through training could produce an additional 1-3"
of rainfall with locally higher amounts. Flash flooding is
possible.
Discussion...GOES-E visible imagery this evening shows a large
closed low centered over Missouri which is slowly drifting
eastward, while a downstream moisture plume funnels northward from
the Gulf of Mexico. Within this moisture plume, PWs have been
measured by GPS at 1.6-1.8" in GA/SC, well above the 90th
percentile for the date according to the SPC sounding climatology.
Instability is slowly climbing across GA/SC south of a WPC
analyzed warm front lifting into NC, and this is reflected by
blossoming Cb noted in the visible imagery coincident with
strengthening reflectivity noted on local radars. Recent rainfall
rate estimates across GA/SC have been as high as 1-1.5"/hr, and
these are likely to persist as activity shifts northward.
As the large upper low advects to the east, downstream mid-level
divergence and height falls will intensify across the
Appalachians, with deep layer ascent also enhanced by RRQ
diffluence within an accompanying upper jet streak. This
impressive lift will help expand coverage of convection through
the evening, with deep unidirectional southerly flow extending
from the Gulf of Mexico acting to resupply moisture and
instability into the region. The impingement of this forcing into
the favorable thermodynamics will likely permit convection to
remain intense even with loss of daylight, and recent runs of the
HRRR and WoFS suggest the potential for N-S oriented bands of more
than 2" of rainfall, with pockets of 3-4" possible due to
training.
7-day rainfall in the Southern Appalachians has been more than
300% of normal according to AHPS, with MRMS measuring pockets of
2-4" of additional rainfall which has already fallen today in
western NC and Upstate SC. This has likely saturated already
sensitive soils, suggesting FFG is even more compromised than the
modeled 1-1.5"/3hrs. Heavy rainfall training across this area
could lead to flash flooding, which is signaled by both increasing
probabilities in the NWM SRF rapid onset flooding product, and
HREF 3-hr exceedance.
Weiss
ATTN...WFO...FFC...GSP...MRX...RAH...RLX...RNK...
ATTN...RFC...LMRFC...MARFC...OHRFC...SERFC...NWC...
LAT...LON 37448075 37438041 37008026 36378032 35678059
35148096 34748172 34638233 34628305 34748351
34978390 35328392 35558332 35798263 36088207
36478189 37258150
Last Updated: 541 PM EDT Thu May 26 2022
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