Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 260120
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
920 PM EDT Tue Jul 25 2017

.SYNOPSIS...
High pressure will build into the Mid Atlantic tonight before
moving offshore Wednesday. A cold front will approach the area
Thursday before passing through Friday into Friday night. High
pressure is expected to return for the weekend.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
High pressure is centered over the eastern Great Lakes this
evening, and with its eastward progress tonight, a light onshore
flow will eventually develop. Upper trough axis is moving
offshore now, and while stratocu has retreated closer to the PA
border, it may not completely exit northeast Maryland. The
onshore flow beneath the subsidence inversion may allow the
clouds to spread back westward, but it looks like they will
remain east of the Blue Ridge (if even that far west). Patchy
fog may develop where there are clear skies and light winds
(most likely western valleys), although there`s not a strong
signal in model data.

Light showers which have been observed over New Jersey and
surrounding areas may eventually spread westward to the
Chesapeake Bay late tonight into Wednesday morning, where the
deepest moisture (albeit still only 500 ft or so deep) will
reside. Sprinkles may be a better expectation. Low temperatures
will be in the 60s for most locations.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH FRIDAY NIGHT/...
Low Fog/stratus will mix out during the late morning or early
afternoon Wed. No wx is expected in the afternoon as subsidence
inversion will remain quite strong. A warm front will lift
through the area Thu with warm humid air moving in. Scattered
showers/t-storms expected in the afternoon mainly in the west,
then widespread showers/t-storms Thu night into at least the
first half of Fri as wave of low pressure moves across. Still
uncertainty in timing of frontal wave moving across and
instability available given expected widespread clouds and
showers. Both a severe and flash flooding risk are present with
flash flooding having higher odds at this time given potential
for repeated activity.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
A closed upper level low is forecast to swing across the Mid-
Atlantic region Saturday. Low pressure along a cold front will
likely be moving south of the Mid-Atlantic region. Showers may
linger into Saturday until the upper level trough axis swings
through by Saturday evening. High pressure will move into the region
behind the departing sfc low Saturday night. High pressure will
likely be in control into the start of the work week.

&&

.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
BKN stratocu may never completely exit Baltimore area. The
question is whether MVFR cigs in NJ/NE PA will move into the
area with the introduction of onshore flow. Feel this is most
likely at MTN, with a conditional threat (SCT in TAF) at BWI,
DCA, and IAD. Patchy light fog also possible at CHO and MRB,
although there`s not a strong signal in guidance.

VFR on Wednesday, with another chance of fog near MRB/CHO
Wednesday night.

Showers and t-storms likely Thu night and Fri with flying
restrictions likely at some point.

Improving weather Saturday night into Sun.

&&

.MARINE...
Winds will continue to diminish through Wed night and
begin to strengthen Thu afternoon into Sat. SCA conditions are
possible during this time. SMWs may also be required due to
potential for convection.

Small craft conditions possible Saturday into Sunday, but winds
should be on the downward trend by Sat night.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...LFR
NEAR TERM...ADS/LFR
SHORT TERM...LFR
LONG TERM...HSK
AVIATION...ADS/HSK/LFR
MARINE...HSK/LFR



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