Mesoscale Precipitation Discussion 0697
NWS Weather Prediction Center College Park MD
213 AM EDT Mon Aug 20 2018

Areas affected...North Carolina

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

Valid 200613Z - 201120Z

Summary...Heavy rain has already fallen in the Triangle Region of
North Carolina tonight, and flash flooding may continue for a
couple more hours. However, new areas of flash flooding may also
develop elsewhere in North Carolina in the early morning hours as
thunderstorms continue to develop. Rain rates of 1-2 in/hr should
be common, with some localized rates up to 3 in/hr possible.

Discussion...The training band of convection in the Triangle
Region was finally beginning to decrease in organization, and the
areas of higher reflectivity were slowly sinking south along with
a convective outflow boundary. This boundary now likely stretched
along a line roughly from Wilson, to Dunn, to Carthage, to
Salisbury. WSW-SW low-level inflow continues, and should continue
to intercept this boundary at close to a perpendicular angle. This
should continue to focus convergence and ascent into south-central
North Carolina, and may allow continued cell growth along the
outflow boundary. As the cells drift north of the boundary and
merge into existing convection, they could produce areas of heavy
rainfall, despite the convective band appearing less focused in
the past half hour on KRAX radar. Of concern would be if heavy
rain became more focused in the corridor including Montgomery,
Moore, Lee, and Harnett Counties, which have received heavy
rainfall recently and have slightly reduced flash flood guidance.

Another area of potential flash flooding would be in eastern North
Carolina, as convective coverage has rapidly increased in the
primary belt of 925-850mb moisture transport. The low-level flow
is slightly stronger in these areas, and the precipitable water
values are a little higher -- above 2 inches per CIRA blended TPW.
Convective bands in this region may be favored for training as the
flow is favorably aligned from a southwesterly direction up
through around 6km AGL. And rain rates could be higher given the
generally higher moisture content. KMHX radar has already
estimated rain rates approaching 3 in/hr just west of New Bern
with a convective cluster that began to exhibit backbuilding
characteristics and stalled near the Neuse River.

Overall, rain rates should be sufficiently high in the strongest
convection in North Carolina to pose a continued flash flood risk
through the early morning hours.

Lamers

ATTN...WFO...GSP...ILM...MHX...RAH...

ATTN...RFC...SERFC...

LAT...LON   36138013 35777932 35687851 35707743 35907607
            35237601 34647696 34427799 34837939 35288099
            35838115