Mesoscale Precipitation Discussion 1064
NWS Weather Prediction Center College Park MD
616 AM EDT Thu Sep 26 2024
Areas affected...eastern GA, Upstate SC into the southern/central
Appalachians
Concerning...Heavy rainfall...Flash flooding likely
Valid 261015Z - 261445Z
SUMMARY...Flash flooding, with locally significant impacts
possible, should be expected for portions of the southern
Appalachians this morning. Training of heavy rain is also likely
to produce areas of flash flooding for other portions of the
Southeast through 14Z.
DISCUSSION...Regional radar imagery at 10Z showed an axis of heavy
rainfall with embedded mesoscale circulations extending from
east-central GA along I-16 (Laurens and Treutlen counties)
northward into far Upstate SC and western NC, along the southeast
facing slopes of the Blue Ridge Mountains. MRMS-estimates
indicated rainfall rates of 1 to 1.5, locally up to 2 in/hr over
the past 1-2 hours within this axis. In addition, 24 hour
estimates from MRMS showed 4 to 8 inch rainfall totals from Oconee
County in far Upstate SC into McDowell County in western NC. The
axis of heavy rain has been co-located with an area of strong low
level moisture flux convergence centered from eastern and northern
GA into western NC where 09Z SPC mesoanalysis data showed ~500
J/kg MUCAPE but with higher values of instability closer to the
Southeast coast (1000+ J/kg). Precipitable water values ranged
from 1.7 to 2.3 inches across the region (higher toward the
southeast), with an area of strong upper level divergence located
within the right entrance region of a nearly stationary upper
level jet max located east of a closed low positioned over the
Lower OH Valley.
Short term forecasts from the RAP show very little movement to the
axis of low level moisture flux convergence over GA/SC/NC over the
next 2-4 hours. Given little change in the forcing mechanisms in
place, heavy rain potential looks to continue over the next couple
of hours across many of the same locations already seeing heavy
rain. The biggest change is a forecast minor reduction in the
available instability, already somewhat low, over inland
locations. Rainfall rates of 1-2 in/hr may reduce in magnitude but
areas of heavy rain are likely to continue, overlapping with areas
that have already seen heavy rainfall and are experiencing ongoing
flash flooding. Additional rainfall totals of 2-4 inches are
expected through 14 to 15Z with locally significant flash flooding
possible across portions of the Blue Ridge from Upstate SC into
western NC.
Otto
ATTN...WFO...CAE...CHS...FFC...GSP...JAX...MRX...RNK...
ATTN...RFC...LMRFC...OHRFC...SERFC...NWC...
LAT...LON 36628109 36318087 35428126 34578160 33488154
32718152 31958196 31978300 33478369 34918367
36068281 36588194
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