868
AWUS01 KWNH 181852
FFGMPD
VAZ000-NCZ000-WVZ000-SCZ000-190050-

Mesoscale Precipitation Discussion 0289
NWS Weather Prediction Center College Park MD
251 PM EDT Sat May 18 2024

Areas affected...Southwest VA...Much of Western and Central NC

Concerning...Heavy rainfall...Flash flooding possible

Valid 181850Z - 190050Z

SUMMARY...Scattered slow-moving areas of showers and thunderstorms
are expected to develop this afternoon and continue into the
evening hours. Rainfall rates of 1 to 2 inches/hour and slow
cell-motions will foster a localized and generally urban concern
for flash flooding.

DISCUSSION...Early-afternoon visible satellite imagery shows
convective initiation underway across the higher terrain of the
Blue Ridge from southwest VA down into northwest NC as small-scale
terrain induced circulations and differential heating work in
tandem with a gradually destabilizing boundary layer for
convection to develop.

Meanwhile, surface observations shows a quasi-stationary front
draped across the region with a wave of low pressure currently
noted along the front just west of Greensboro. MLCAPE values
across western and central NC have already risen to locally over
1000 J/kg with a rather moist airmass in place characterized by
PWs of locally 1.5+ inches from near the NC Triad and points east.

The convection initiating near the Blue Ridge should tend to
develop off to the southeast with time, with additional convective
development expected in close proximity to the aforementioned low
center and the greater NC Triad over the next few hours where
low-level convergence/forcing will tend to be relatively stronger.

Cell-motions are expected to be quite slow given the weak steering
currents aloft, and this coupled with rainfall rates that will be
capable of reaching 1 to 2 inches/hour will support some spotty
storm total amounts that could reach 3 to 4 inches in just a
couple of hours. This is supported by the 12Z HREF guidance.

Given the rainfall amounts, and moist antecedent conditions and
locally high streamflows (as suggested by NASA SPoRT and USGS data
respectfully), there should be at least a localized threat for
flash flooding. However, the greatest sensitivities will be to the
urban corridors and this will include the NC Triad region
involving Greensboro and the Raleigh-Durham area. Areas south and
east of the NC Triad will also have a regional threat for
slow-moving convection going into the evening hours given
proximity of the front, and thus some isolated flash flooding will
be possible here too.

Orrison

...Please see www.wpc.ncep.noaa.gov for graphic product...

ATTN...WFO...AKQ...GSP...MHX...RAH...RNK...

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

LAT...LON   37538052 37518019 37308005 36837994 36487970
            36387850 36157759 35897707 35477669 35137681
            34937738 34987804 35057923 35258075 34988206
            35088275 35558261 36318150 37228091