Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 181308

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

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


Upper-level low pressure over the western Great Lakes will remain
nearly stationary through this afternoon. Low pressure is
reflecting at the lower levels of the atmosphere near the
Appalachian Mountains and this will also remain nearly stationary
throughout this afternoon. Another upper-level disturbance will
pass by well to our south off the Carolina coast. High pressure
will remain centered over New England and a northeast flow will
continue to usher in unseasonably cool conditions for this time of
year. Plenty of clouds are also expected due to moisture being
trapped underneath the subsidence inversion...thanks to the low-
level easterly flow.

Periods of rain are expected across the Allegheny and Potomac
Highlands as well as portions of the Shenandoah Valley...eastern
West Virginia and western Maryland through this afternoon...closer
to the upper-level low. However...the rest of the area may end up
split in between this system and the one to the south.
Therefore...much of the day may turn out dry for the Washington
and Baltimore Metropolitan areas into southern Maryland and
central Virginia. Still will allow for the chance for light rain
given the moisture that is trapped underneath the subsidence
inversion. Any rainfall amounts will be light.

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.


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.


Rain will begin moving 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.


VFR conditions this morning. Cigs will likely drop to MVFR levels
later this afternoon into this evening as an upper-level
disturbance passes through the area. Light rain is
possible...especially across KCHO and KMRB.

MVFR cigs expected overnight 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.


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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