Area Forecast Discussion
Issued by NWS Sterling, VA
FXUS61 KLWX 271855
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
255 PM EDT Mon Mar 27 2017
A cold front will cross the area late Tuesday. High pressure
builds over the region Wednesday into Thursday. Another
disturbance will approach the area late Thursday into early Saturday.
.NEAR TERM /THROUGH TONIGHT/...
While it took some time...visible satellite imagery and surface
observations indicate that the stubborn marine stratus layer
has all but eroded from the area as warm front lifted northward
into PA. As expected...this has led to a rapid warmup...with
highs in most places well into the 70s by late afternoon (with
even some U70s possible across central VA and the Shenadoah
CAPE gradient sets up this afternoon roughly from Montgomery
County to the south...with ~500-700 J/kg of MUCAPE (~250 J/kg
MLCAPE) expected across central/northern VA into south central
MD. Thus, could be a few scattered thunderstorms this afternoon
across these areas along the differential heating boundary. 0-6
km effective bulk shear generally near 30-35 kts suggests a
storm could briefly become somewhat semi-organized. Though, lack
of deep quality moisture coupled with long skinny CAPE profiles
and relatively weak winds aloft likely limit any stronger
thunderstorms. Gusty winds and small sub-severe hail would be
the primary threats in any activity this afternoon. Thunderstorm
chances rapidly decline after sunset.
Isolated (to perhaps scattered at times) shower chances continue
through the overnight. Though, think most places will remain
dry through much of the night. Best chance for precipitation
arrives across the SW after midnight and then spreads NE
through the morning as shortwave approaches. There could be
some isolated thunder with this elevated activity.
In addition...there could be some patchy dense fog tonight as
we decouple and low-level moisture remains. Guidance continues
to indicate the most likely location for fog would be from DC
and to the NE.
.SHORT TERM /TUESDAY THROUGH WEDNESDAY/...
Another warm day tomorrow as moisture/warmth pools ahead of
cold front. SPC continues to delineate the southern half (i.e.,
from DC south) and east of the Blue Ridge in a marginal risk
for severe weather. While CAPE is higher tomorrow (e.g.,
~500-800 J/kg MLCAPE with the higher amounts to the south) shear
is also considerably less (i.e., ~20-25 knots). Thus, expect
the possibility of a few poorly-organized marginally-severe
thunderstorms across the risk area. Any threats expected to be
isolated and confined to damaging wind gusts and small hail.
Chances for precipitation should be ending late Tuesday evening
as the shortwave moves off the coast and cold front pulls away
from the area. High pressure returns Tuesday night and Wednesday.
Temperatures Wednesday cool nearly ten degrees from Tuesday (though
still remain above normal).
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Thursday starts out dry as a high pressure builds into the NE
CONUS. Meanwhile, a strong closed low will be moving northeast
from the southern plains and into the Mid-Atlantic. This system
will bring decent amounts of moisture into the region, with
rain starting Thursday night and remain into sometime Saturday.
Many GEFS members bring the highest QPF amounts on Friday night.
Conditions become dry behind this system Saturday and into
Monday. High temperatures will be in the 50s and 60s, and lows
in the 40s.
.AVIATION /18Z MONDAY THROUGH SATURDAY/...
VFR expected through the remainder of today...with perhaps a
passing shower or thunderstorm this afternoon. Chance is too
low to include in the TAF...but most likely terminals would be
IAD/DCA/CHO. Dense fog is also possible at some of the
terminals overnight. Best chances for fog or low clouds at
IAD/MTN/BWI/DCA. Kept TAFs at IFR for now...though if fog does
occur there could be some sub-IFR conditions.
A chance for thunderstorms returns to the terminals Tuesday
afternoon...with the possibility of gusty winds and small hail
in the strongest storms. Conditions should improve late Tuesday
evening through Wednesday with the return of VFR as high
pressure builds into the area.
Dry/VFR conditions expected for Thursday before rain approaches
over the area Thursday night, possibly bringing sub-VFR
conditions over the terminals Friday into early Saturday.
SCA currently in effect for the southern portion of the waters
through late afternoon. In addition, there is a low probability
of an isolated thunderstorm with gusty winds late this afternoon.
Thunderstorms will again be possible Tuesday afternoon, some of
which could produce SMW-level winds. Wind gusts will then
increase Tuesday night into Wednesday behind frontal
passage...with SCA possible as early as early Wednesday
morning...but likely during the day Wednesday. Winds expected to
diminish later Wednesday.
Dry conditions expected for Thursday before rain approaches over
the area Thursday night bringing showers over the waters into part
of Saturday. Wind gusts will be near the small craft advisory
threshold mainly Friday night into Saturday... therefore SCA possible
MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ533-