Mesoscale Precipitation Discussion 0643
NWS Weather Prediction Center College Park MD
340 PM EDT Sun Aug 12 2018

Areas affected...Virginia, Northern North Carolina

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

Valid 121939Z - 130130Z

Summary...Several lines and clusters of storms continue to make
eastward progress into Virginia. They should continue to push east
to the Tidewater region this evening, and build into northern
North Carolina. These storms may produce rain rates of around 2
in/hr at times and the potential for flash flooding, particularly
if aligned with urban areas.

Discussion...Regional radars showed several organized convective
clusters and lines pushing into central Virginia now, and they
were beginning to arrive in a plume of deeper moisture. As
indicated by the GOES-16 Simple Water Vapor and Air Mass RGBs,
this plume of deeper moisture was centered on Virginia as well as
central North Carolina, with some drier air to the west, and drier
air aloft in eastern North Carolina. The deeper moisture should
support rain rates to around 2 in/hr in some cases, which could
cause flash flooding. Some of the lines of thunderstorms, though,
were showing signs of increased forward propagation, especially
the one approaching Fredericksburg as of 1930Z. This may reduce
the flash flood threat somewhat. However, with access to strong
instability (MLCAPE 2000-2500 j/kg) and around 40 knots of
effective deep layer shear, thunderstorms should remain relatively
organized and continue to push east and southeast into the early
evening hours.

One area to watch would be around Richmond, where the 12Z HREF
blended mean rainfall from 21-03Z is around 3 inches, with around
one-quarter of the members showing rainfall in excess of 5 inches.
Accelerating compact storm cluster to the north could reinforce a
thunderstorm outflow boundary near the I-64 corridor and
potentially aid in focusing training convection later in the
afternoon or early in the evening.

Lamers

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

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

LAT...LON   38817778 38807704 38327670 37527625 36617609
            35987822 35747956 35708089 36258158 37128021
            37977939 38287850