Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 240046
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
846 PM EDT Thu Jun 23 2016

.SYNOPSIS...
A low pressure system will move east across the region tonight and
Friday. High pressure will build in from the north Saturday and
Sunday. A cold front will cross the region early next week.

&&

.NEAR TERM /THROUGH FRIDAY/...
Surface features are diffuse at this time, but numerous strong to
severe thunderstorms have been feeding off of a stalled boundary
across southern Virginia and West Virginia. That area has high
CAPE values (3000 j/kg per recent mesoanalysis) as well as
precipitable water values approaching 2 inches. Although shear has
been high locally, mean layer instability and forcing have been
lacking, in addition to a dry mid layer. A few showers and
thunderstorms have been able to develop in late day heating across
southern Pennsylvania, and these may clip northern Maryland this
evening. Otherwise, there isn`t much radar activity at the present
time.

There is too much precipitation too close to the Central
Shenandoah Valley/adjacent eastern West Virginia panhandle to pull
PoPs there, but have scaled back. If current trends hold, we will
be able to let the Flood Watch drop at 10 pm.

Overnight, patchy fog may develop in many areas. Approaching
trough may also keep some showers or isolated thunderstorms going
through the night. Am limiting that potential to south of a
Petersburg WV to Fredericksburg VA line. Lows will be in the 60s.

Friday, the upper level trough passes through and the front should
still be lingering especially in central VA. There may be enough
forcing and CAPE to trigger some additional strong to severe
thunderstorms but uncertainty is high. Best odds favor central VA
on south. Highs should rebound into the 80s.

&&

.SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/...
High pressure will push southward into the region Friday night and
dominate through the weekend as the center shifts eastward to our
north. Any lingering showers should die out Friday night.
Generally dry Saturday though lingering moisture and easterly
upslope flow along with heating may spark a shower in the
mountains. Sunday looks completely dry as ridge aloft builds
directly overhead. Warming trend will develop Sunday though
tempered by a somewhat easterly flow.

&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...
High pressure will remain in control into early next week. 590+
DM 500 MB heights suggest decent heat. Warm and humid conditions
briefly envelop the region Monday before a cold front moves in
from the west, which may trigger a round of scattered showers and
thunderstorms.

High pressure and seasonably cooler temperatures will return for
the middle part of next week.

&&

.AVIATION /00Z FRIDAY THROUGH TUESDAY/...
VFR conditions prevail at the terminals this evening. Don`t
believe showers and thunderstorms will be an impact. There`s a
continuous line south of CHO, with additional scattered activity
north of MTN. The northern batch should dissipate before midnight.
While the southern activity will last longer, it too will weaken
while remaining south of the area.

Patchy fog may reduce cigs and vis later tonight into Friday
morning. Low levels are humid, but am uncertain how much
radiational cooling we will see. Focused more on vsbys vs
cigs, assuming that there will be thin spots in cloud decks that
aren`t all that low just yet...taking a predawn period of IFR at
climo preferred locations (IAD/MRB/CHO) and MVFR elsewhere. IFR
could be more widespread, and LIFR possible. However confidence in
a more drastic solution lacking at this time.

Thunderstorms may redevelop Friday afternoon. Don`t have a good
feel for specifics yet, so aside from P6SM -SHRA at CHO have
mainly kept the risk out of the TAFs at this point.

Fog may redevelop again late Friday night into Saturday morning
before air mass can dry out. After that, VFR should prevail
through the rest of the period.

&&

.MARINE...
Due to ongoing cloud cover, winds have been below 10 kt for the
most part. Expect sub-SCA conditions this evening through Sunday
as high pressure slowly builds in from the north. However,
showers and thunderstorms will remain possible again on Friday
with SMW`s possible. Storm-free Saturday and Sunday.

Southerly channeling and small craft conditions possible Monday
ahead of a cold front.

&&



.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...Flash Flood Watch until 10 PM EDT this evening for VAZ025-026-
     036>038-503-504-508.
WV...Flash Flood Watch until 10 PM EDT this evening for WVZ505-506.
MARINE...None.

&&

$$
SYNOPSIS...RCM
NEAR TERM...HTS/RCM
SHORT TERM...RCM
LONG TERM...DFH
AVIATION...HTS
MARINE...HTS/RCM/DFH



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