AWUS01 KWNH 211556
FFGMPD
NCZ000-SCZ000-GAZ000-212145-
Mesoscale Precipitation Discussion 1102
NWS Weather Prediction Center College Park MD
1155 AM EDT Fri Aug 21 2026
Areas affected...Much of the Carolinas...Adj. East Central
Georgia...
Concerning...Heavy rainfall...Flash flooding likely
Valid 211545Z - 212145Z
SUMMARY...Environment for colliding boundaries and sufficient
organization to support 2-2.5"/hr rates with occasionally locally
higher 3"/hr rates probable. Potential for above normal scattered
incidents of 2-4" likely to result in localized flash flooding,
especially near multiple large metro areas through the Piedmont.
DISCUSSION...A favorable moist and unstable environment with
multiple sufficient dynamic elements to help generate strong,
efficient rainfall producing thunderstorms exists across the
Carolinas this afternoon. GOES-E WV suite shows a convectively
enhanced shortwave/MCV at the base of the larger scale trough
currently in Western NC along the eastern slopes of the
Appalachians with a positive tilt trough/orientation back across
central GA. This wave is lifting northeastward behind the initial
convective line. This convective line remains progressive across
SW VA with an outflow/convergence boundary draped southward across north-central NC. A surface front intersects the coast near
Jacksonville, NC before reaching a well defined surface low
northeast of Florence, SC; while the upstream stationary front
remains well defined toward Augusta, GA. However, a differential
heating boundary exists across north-eastern NC (east of the
aforementioned outflow boundary), so while post-frontal, solid
insolation and Tds in the low to mid-70s remain allowing for an
expanding wedge of SBCAPEs across much of eastern and central NC
with tight gradients and rising to 2500-4000 J/kg from near
Charlotte to the SE NC coast. The last piece of forcing is
related to failed convection/outflow boundaries across central SC
lifting northward off the surface frontal boundary; though
sea-breeze may be a contributing factor though not established at
this time.
Being at the base of the long wave trough with elongated
shortwave/vorticity feature along the Appalachians will support
and expanding right entrance region mainly across NC throughout
the early afternoon providing further divergence and deep layer
effective bulk shear around 25-30kts, suggesting a bit more
overall organization and less pulse-like up/downdrafts further
north across the area. However, with overall TPW values of
2-2.25" pooled along the boundary and toward the Atlantic coast,
the modest surface to boundary layer directional convergence may
over-come the weaker overall speeds but allow for quick vertical
ascent and moisture loading. Quick conversion to 2-2.5"/hr rates
are initially possible near the boundary. However, with the
shear/outflow and multiple colliding boundary potential, slow
moving, merging clusters should evolve allowing for localized
enhanced residency and occasional up-tick in rates toward 3"/hr
locally. By 21-22z, there should be scattered areas of localized
2-5", with higher areal concentration generally north and east of
the surface low, near the front.
Hydrologically, the most prone areas/lowest FFG align with the
Fall-line from Augusta to Columbia to Charlotte to Raleigh-Durham
all of which have a solid potential of being intersected by
thunderstorms. Given hourly FFG values less than 2" and 3hr
values of 2-2.5" if directly under the slow moving cells will
likely result in incidents of rapid inundation/flash flooding.
While FFG values are much higher eastward into the Coastal Plains,
FFG value of 3-4"/3hrs still may be exceeded given HREF
probability of 3"/6hr remains above over 50-60% within 40km of any
given point in the MPD area of concern and further expands to over
80% if extending out to 00z. All in all, a wet afternoon/evening
will see incidents of flash flooding but they may be more locally
focused at least initially.
Gallina
...Please see
https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!DZ3fjg!8ETGedN8zjbOvNmTcDZE9PGlmhPw2h4zc9p77JvLDVB5jJ3O5FQgCZASfMQ4ZiX4PmRtyuuTpvDqkD5c_W12gWv75E8$ for graphic product...
ATTN...WFO...CAE...FFC...GSP...ILM...MHX...RAH...
ATTN...RFC...ALR...NWC...
LAT...LON 36167792 35707692 34857645 34687682 34417736
34187768 33807790 33737871 33767967 33498070
33138221 33528310 34688278 35818112 36087928
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