735
AWUS01 KWNH 171736
FFGMPD
PAZ000-MDZ000-VAZ000-WVZ000-172335-

Mesoscale Precipitation Discussion 0283
NWS Weather Prediction Center College Park MD
135 PM EDT Fri May 17 2024

Areas affected...Portions of the Central Appalachians/Blue Ridge

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

Valid 171735Z - 172335Z

SUMMARY...Slow-moving shower activity with heavy rainfall rates
will tend to increase in coverage this afternoon across areas of
the central Appalachians including parts of the Blue Ridge. This
coupled with moist antecedent conditions will promote a threat for
some instances of flash flooding.

DISCUSSION...A broad mid to upper-level trough over the OH Valley
will continue to move gradually off to the northeast today toward
the central Appalachians. Some generally weak DPVA/forcing
associated with this will be interacting with modest
diurnally-enhanced instability and a relatively moist airmass for
broken areas of heavy showers.

Radar imagery already shows some locally heavy shower activity
impacting areas of southeast OH into southwest PA and down through
central WV as the leading edge of relatively stronger forcing
aloft arrives. Some expansion of this activity with a general
increase in rainfall rates can be expected this afternoon as
MUCAPE values increase to locally over 1000 J/kg and couple with
smaller scale areas of more targeted moisture convergence in
vicinity of a quasi-stationary front draped over the higher
terrain.

Relatively moist southeast flow will also provide a localized
orographic component to the rainfall threat with southeast-facing
slopes of the central Appalachians and portions of the Blue Ridge
seeing pockets of more focused low-level forcing for slow-moving,
but heavy shower activity.

The rainfall rates should be efficiently high given the overall
depth of moisture through the vertical column which was evidenced
in 12Z RAOB data across the broader OH Valley this morning in
connection to the aforementioned trough. The modest increase in
instability will favor some shower activity capable of producing
rainfall rates of 1 to 1.5 inches/hour with the stronger cells.

Given the overall weak steering flow, and orographic nature of
some of the convection, there may be a sufficient level of
persistence to the showers to yield some excessive totals. This is
being supported by the 12Z HREF guidance which suggests some of
the heavier rates focusing over parts of southwest PA through the
eastern WV/MD panhandles and northwest VA in vicinity of the Blue
Ridge. Some spotty 2 to 3+ inch rainfall totals will be possible
by early this evening, and with moist antecedent conditions/lower
FFG values in place, some instances of flash flooding will be
possible.

Orrison

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

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

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

LAT...LON   40787982 40647909 39927823 39017800 38467818
            37967900 37958023 38148058 38558072 39468048
            40398038