Mesoscale Precipitation Discussion 0742
NWS Weather Prediction Center College Park MD
153 PM EDT Sat Sep 01 2018

Areas affected...eastern WV into western/central VA

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

Valid 011752Z - 012345Z

Summary...Slow moving thunderstorms will have the potential to
produce 2-4 inches a few locations from eastern WV into western
and central VA. Given low Flash Flood Guidance (FFG) values across
the region, flash flooding will be possible.

Discussion...Visible satellite and radar imagery showed scattered
thunderstorms underway across the WV/VA border as of 1730Z with a
general mean movement off toward the northeast at 10-20 kt.
Forecasts of 850-300 mb mean winds showed 10-15 kt across the
central/northern WV/VA border with flow weakening to 5-10 kt
farther south along the border by 21-00Z, indicative of slower
storm movement. Precipitable water values from 17Z were between
1.5 to 1.7 inches across the WV/VA border into central VA, but
CIRA layered PW imagery showed a deep layered connection of
moisture from the central Gulf Coast, where tropical moisture
resided, into the central Appalachians with forecasts for
increased precipitable water through 00Z approaching 2 inches in a
few locations across the Mid-Atlantic region.

Forecast RAP soundings across western VA indicate LFC-EL mean flow
of 5-10 kt which is similar to or slightly weaker than 850-700 mb
which may promote a few areas where thunderstorms can stall. 2-4
inch totals are expected in a few locations which would fall over
a 1-3 hour period. Given the high moisture environment and low FFG
values of 1.5 to 2.5 inches in 3 hours, some exceedance of FFG is
possible through the remainder of the afternoon. There will be a
near term flash flood threat across the higher terrain over the
next few hours with a localized threat into portions of
west-central VA by early evening with increasing CAPE/moisture and
slow storm motions.

Otto

ATTN...WFO...AKQ...LWX...PBZ...RLX...RNK...

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

LAT...LON   39247908 39127840 38777816 38287820 37817838
            37157893 36777963 36518064 36478109 36518139
            36618159 36808161 37108158 37588116 38138050
            38807995 38997954