632
AWUS01 KWNH 171513
FFGMPD
VAZ000-NCZ000-172030-

Mesoscale Precipitation Discussion 1029
NWS Weather Prediction Center College Park MD
1112 AM EDT Tue Sep 17 2024

Areas affected...Southeast VA...Northeast NC...

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

Valid 171510Z - 172030Z

SUMMARY...South to north training and efficient rainfall rates up
to 2-3"/hr approaching urban centers of SE VA pose possible
localized flash flooding/rapid inundation flooding through early
afternoon.

DISCUSSION...Active convection this morning over the Pamlico River
supported a tightening of the surface triple point as well as an
associated boundary layer to 850mb low.  While these two features
have separated with the occluded low still remaining south toward
the mouth of the Pamlico River; the elevated circulation has
lifted northward over toward the Chowan/Albermarle Rivers
continuing to lift north.  The trailing tail has become highly
convergent with easterly surface to 850mb both north of the warm
front (near Roanoke Island) lifting north and veered southeasterly
flow out of the warm sector over the central sound and Atlantic
east of the Outer Banks.  Tds in the mid to upper 70s with temps
increasing to the mid-80s in the warm sector is supporting
increasingly unstable air with MLCAPEs over 1500 J/kg fueling
stronger updrafts within the strengthening deep layer convergence
axis.  Total PWats of 2-2.25" are more than sufficient (loaded
with 1-1.2" in the lowest sfc-850mb per CIRA LPW) with the
strength of flux to support 2-2.5"/hr perhaps occasionally ticking
up to 3"+/hr for short-durations and highly localized.

Deep layer steering will support a south to north training that
may result in a few hours of training.  This may result in 3-5"
localized totals across far SE VA and NE NC; however, there is
some uncertainty that propagation to the east due to the strength
of inflow may reduce the training duration but also shift the
focus along or just offshore, limiting the flash flooding/rapid
inundation risk.  While much of the area is sandy soils (FFG
3-4"/3hrs) and supports higher infiltration, rates over 3"/hr or
even proximity to urban centers have a higher probability of
inducing flash flooding.   Hi-Res CAMs are more persistent in
allowing for more westerly cell motions expanding the flooding
threat westward; however, nearly all do not resolve this low level
wave lifting north acting like a barrier as well as reducing
insolation with increased cirrus canopy and therefore unstable
downstream air.  The 12z ARW2 seems to handle this wave best of
the overall solutions but trends appear west compared to
observations.  Bottom line, these variations due reduce overall
confidence in precise placement but the rates/potential totals
should result in localized flash flooding.

Gallina

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

ATTN...WFO...AKQ...MHX...

ATTN...RFC...MARFC...SERFC...NWC...

LAT...LON   37847641 37717571 37347562 36797581 36067559
            35427534 35247557 35717611 36137646 36437669
            36857687 37347693 37667677