Mesoscale Precipitation Discussion 0641
NWS Weather Prediction Center College Park MD
1214 PM EDT Sun Aug 12 2018

Areas affected...Nrn/Wrn Virginia, Far Ern West Virginia, Far NW
North Carolina

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

Valid 121613Z - 122030Z

Summary...Thunderstorms developing in the central Appalachians
will continue to increase in coverage and begin to move east into
the valleys and Piedmont of central Virginia this afternoon. The
storms should be capable of producing localized very heavy rain
rates, perhaps approaching 3 in/hr at times, which could lead to
flash flooding.

Discussion...GOES-16 satellite showed an early start to convective
development in the central Appalachians today, with numerous
thunderstorms already beginning to form near the WV-VA border. The
early start was likely being aided by some stronger forcing for
ascent, and a still moderately unstable air mass in place across
the region. A prominent +PV anomaly, evident on water vapor
satellite channels, was digging S/SE over Ohio at the moment, and
models projected it to continue digging into West Virginia later
today. This was also leading to an increasing upper level jet
streak from the Mid Atlantic up the Eastern Seaboard, and Virginia
should be squarely in the right entrance region of this jet
streak. Thus, there is certainly support for large scale ascent,
and the early convective initiation confirms that.

Hi-res models show an increasing concentration of convection in
the 18-21Z time frame in western Virginia, with the 12Z HREF
indicating 50+ percent chances of over 2 inches of rain in that
time frame along the I-81 corridor from Roanoke to Harrisonburg,
and locations just east of that. In fact, the hi-res models show
some significant hourly rain rates with the most organized
convective clusters. On many of the models, they peak around 3
in/hr, which would be more than sufficient to produce flash
flooding. An area of model agreement on more substantial rain
rates is across northwest Virginia, from near a more concentrated
band of convection at the moment just NW of Harrisonburg, down
into the area near Charlottesville and Culpeper. Flash flood
guidance also happens to be reduced in those same areas, so that
could be a favored area for flash flooding today. However, flash
flooding will be possible through the entire outlined area.

Lamers

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

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

LAT...LON   39057847 38717748 37917782 37297853 36717942
            36398012 36088077 35918156 36158211 36528225
            37128257 37568132 38268020 38757935