AWUS01 KWNH 271313
FFGMPD
VAZ000-NCZ000-WVZ000-SCZ000-GAZ000-TNZ000-271810-

Mesoscale Precipitation Discussion 1076
NWS Weather Prediction Center College Park MD
913 AM EDT Fri Sep 27 2024

Areas affected...Upstate SC, western NC, far northeastern TN,
southwest VA, and southern WV

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

Valid 271310Z - 271810Z

SUMMARY...Life-threatening flash flooding and the likelihood of
catastrophic impacts to continue across much of the southern
Appalachians through at least early this afternoon with an
additional 2-4" of rain.

DISCUSSION...The center of Tropical Storm Helene is racing
northward and entering Upstate SC as of 1245Z. Along with it
resides an area of 2-3" per hour rainfall rates (via MRMS) in what
is the leftovers of a northern eyewall over western NC. Peak
3-hourly rainfall observations from NWS/AWOS/ARL sites also
confirm these amounts. This torrential rainfall is occurring over
a region that has experienced widespread rainfall amounts of 5-12"
over the last 24 hours, making for a particularly dangerous and
life-threatening situation as ground conditions are already
oversaturated and FFGs remain extremely low. Flash flooding is
ongoing and will likely continue/worsen over at least the next few
hours across western NC.

A large area of 60-80 kt southeasterly 850mb winds per the 11z RAP
on the eastern periphery of Helene are leading to an extremely
favorable upslope enhancement across western NC orthogonal to the
Blue Ridge/southern Appalachians, along with record-breaking PWs
(per the NAEFS ESAT) in the 2-2.5" range surging northward. This
along with nearby MUCAPE values of 500 J/kg advecting northeast
and wet bulb zero heights above 14k feet (near the daily record
for GSO per SPC's sounding climo) will allow for warm rain
processes.

The only positive news is that Helene continues to race north at
30 mph (per NHC) and lead to a quick exit of this extreme
rainfall, with intense rates ending across Upstate SC first by 14Z
and western NC by around 16Z. However, this region will also take
the brunt of the tropical moisture surge and the highest
additional totals. Heavy rain will slide northward as it exits the
western Carolinas and impact regions of southwest VA and southern
WV with rainfall rates of 1-2" per the 06z HREF through 19-20Z.
This region also remains mostly saturated after 1-3" of rain over
the past 24 hours.

Snell

...Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!=
DZ3fjg!6ecx4mCqBJ8EKCSwJa6MWjyHZvbUGxePGOkFskfSW7xeiBJZ65S7AMiTPU4I3Bz9-hEq=
Nh3RMBfd1a3mcT0f0UD9Fhw$  for graphic product...

ATTN...WFO...GSP...MRX...RAH...RLX...RNK...

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

LAT...LON   37928066 37767976 37107967 35968032 35158118=20
            34928231 35008318 35328353 36048310 36828245=20
            37678156=20

=3D =3D =3D
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