937
AWUS01 KWNH 300414
FFGMPD
VAZ000-NCZ000-WVZ000-301010-

Mesoscale Precipitation Discussion 1083
NWS Weather Prediction Center College Park MD
1213 AM EDT Mon Sep 30 2024

Areas affected...east-central VA/NC border into central VA and far
eastern WV

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

Valid 300412Z - 301010Z

Summary...Heavy rain showers are expected to maintain a flash
flood threat for portions of VA into WV over at least the next 3-6
hours. Rainfall rates of 1 to 2+ in/hr are expected, overlapping
with wet antecedent grounds.

Discussion...Regional radar imagery at 0345Z showed an axis of
showers extending from the foothills of the Blue Ridge Mountains
in central VA, southeastward to the east-central VA/NC border
between I-85 and I-95. These showers were warm-topped, only -5 to
-15C on "clean channel" infrared imagery with collision and
coalescence processes dominating and have been rather efficient
despite the fact that the bulk of the available instability is
weak and limited to the 0-6 km AGL layer (via 00Z RNK/IAD and RAP
analysis soundings). MLCAPE was only a few hundred J/kg but
precipitable water values were estimated via 03Z SPC mesoanalysis
data to be 1.6 to 1.9 inches. It appears low level convergence
(925-850 mb) was playing a role in the location of these showers
with some degree of isentropic/orographic ascent aiding in lift.

Short term forecasts of instability from the RAP indicate only
gradual weakening and low level convergence of southeasterly winds
to slowly shift north over the next 3-6 hours. Rainfall rates have
been observed locally over 2 in/hr and similar potential will
exist overnight with slow moving and repeating showers likely to
continue, though some weakening should be expected where
instability is lower or decreases with time.

Much of the area still contains lower flash flood guidance due to
wet antecedent conditions due to rainfall over the past week.
Therefore, while perhaps not widespread in coverage, at least a
localized flash flood threat will be likely to continue into the
night with rainfall rates of 1 to 2+ in/hr at times. Additional
storm totals may exceed 3 inches on an isolated basis.

Otto

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

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

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

LAT...LON   38757826 38247779 37147703 36477710 36337764
            36437820 37157878 37297994 37728022 38337988
            38737935