Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 180730

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
330 AM EDT WED MAY 18 2016

.SYNOPSIS...Low pressure will pass well to the south tonight. High
pressure builds tonight through Friday. Low pressure will impact
the area over the weekend.


.NEAR TERM /THROUGH TONIGHT/...High pressure is located across the Midwest
this morning while a stationary front is to the south of the Mid-
Atlantic. A shortwave trough will move through the Ohio River
Valley this morning.

The Mid-Atlantic region is between two upper level disturbances this
morning with areas of rain to the northwest and southeast. Only a
few showers have been observed overnight with even clearing across
the interior. Patchy fog has been observed. As the northern
shortwave trough moves eastward rain will move across the Potomac
Highlands and Nrn MD early this morning. Rain will then track
eastward across the rest of the region by late morning.
Overall...most of the rain should stay to the west and north of the
forecast area with only light amounts expected across the area this
morning. The one exception is across the Nrn Potomac Highlands where
up to a quarter inch is expected. Northeast winds will continue
today and due to the slow progression of drier air moving into the
region...mostly cloudy conditions are expected through the
afternoon. Rain will taper off by afternoon. Temps will be cool
again...mid to upper 50s to the low 60s across the I-95 corridor.

High pressure continues to build into the region tonight however dry
air will take its time. A chance of rain continues mainly across the
VA Highlands and Shenandoah Valley tonight.


.SHORT TERM /THURSDAY THROUGH FRIDAY/...High pressure will be across
the region Thursday however another upper level disturbance will
cross the region Thursday afternoon. Although there will be some
breaks in the clouds...partly sunny to mostly cloudy conditions
are expected and a few showers can not be ruled out.

Then finally...ridging moves into the Mid-Atlantic briefly on Friday
and mostly sunny conditions are expected for the first part of the
day. Temps will reach the low 70s on Friday before clouds build back
into the region in the afternoon. Showers will approach the SW as
the next system approaches.


into the southwest part of the fcst area Fri evening and spread
slowly to the northeast overnight Fri as overrunning increases
ahead of low pressure moving across the southern mid-Atlc states
Fri night and Sat. Model guidance has trended more progressive
and weaker with accompanying mid-upper level trough through Sat now
showing an open trof but still show development into a large
cutoff low over the Chesapeake Bay Sun night as opposed to Sat
as indicated 24 hrs ago. Given the more progressive nature of the
steadier rains, projected rainfall totals are a little less now
but 1 to 2 inches of rain are still likely. Showery weather still
likely to continue Sun as upper low lingers. Instability daytime
showers and t-storms possible Mon and Tue as cool temps aloft
remain. By Wed, upper low should have weakened considerably and
lifted well to the northeast with model guidance indicating upper
level convergence and sfc ridging establishing over the area
leading to a rain free day.


.AVIATION /07Z WEDNESDAY THROUGH SUNDAY/...Some clearing across the
metro terminals resulted in patchy fog. Clouds are increasing and
fog is dissapating.

Conditions are expected to worsen this morning as rain
approaches the terminals. Cigs will likely drop to MVFR at the
terminals and IFR at CHO. There is a chance IFR cigs may reach
IAD/DCA this morning however confidence is low and cigs should stay
further south. -SHRA will move east across the Mid-Atlantic this
morning however coverage should be scattered with the exception of
MRB. Cigs will likly improve by the afternoon with CHO staying MVFR
into the evening.

MVFR cigs expected tonight into Thursday morning. IFR expected at
CHO. Conditions will improve Thursday becoming VFR by Thursday
afternoon. VFR conditions expected Friday.

MVFR/IFR conditions likely Sat and Sat evening in rain. Conditions
improve late Sat night low pulls out and rain ends. Winds
strengthen from the NNW Sun with gusts to 20 kt.


.MARINE...Sub-SCA conditions expected today and tonight as high
pressure builds into the region. High pressure will move over the
waters Friday resulting in calm winds.

Small craft advisory conditions appear likely Sat through Sun as
pressure gradient tightens in response to deepening low off the VA




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