Mesoscale Precipitation Discussion 0586
NWS Weather Prediction Center College Park MD
626 PM EDT Thu Aug 02 2018

Areas affected...NW VA, W MD, E WV, SC PA

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

Valid 022224Z - 030330Z

Summary...Increasing thunderstorms along and east of the Blue
Ridge Mountains in northern Virginia may begin to repeatedly
affect the same areas and lead to locally heavy rainfall and flash
flooding in those portions of Virginia, and perhaps into western
and central Maryland. Other areas of rain may begin to increase
from eastern West Virginia into southern Pennsylvania. Flash
flooding may be less likely in the immediate future there, but
given wet grounds and elevated streams across the area, flooding
should be considered possible across the entire outlined area.

Discussion...KLWX and KFCX radars showed a quick increase in
convective coverage and intensity along the Blue Ridge Mountains
in northern Virginia. This was also roughly aligned with the
low-mid level mean wind, and thus the developing storms may begin
to train in the confluent flow. The environment over northern
Virginia and central Maryland is characterized by moderate
instability (1500 j/kg MLCAPE) and deep moisture (PW around 2
inches), which should support organized bands of thunderstorms
with the potential for rain rates up to around 2 in/hr. Flash
flood guidance in this area is substantially reduced, with up to
an inch of rain in the preceding 24 hours, and over 3 inches of
rain in the past week. Therefore, training storms could pose a
threat for additional flooding in these areas.

Elsewhere across the area, weaker rain bands were developing in
eastern West Virginia and into southern Pennsylvania. These were
likely weaker due to less access to the primary reservoir of
instability (further east). Nevertheless, increasing forcing into
the evening hours may support a slow uptick in rain coverage and
intensity. Streamflow in this area is generally above the 90th
percentile, so even moderate rain, sustained over several hours,
could lead to additional flooding issues. Furthermore, some of the
hi-res models indicate that the stronger convection may begin to
drift back to the west with time; while that may not be likely, it
is a possibility and would increase the flash flood potential if
that were to occur.

Lamers

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

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

LAT...LON   40247747 39737692 38637761 37997819 37277909
            37357964 37837978 38388017 39257973 40107889