Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 170140
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
840 PM EST Mon Jan 16 2017

.SYNOPSIS...
High pressure will build over the area overnight. A stationary
front over the southern mid-Atlantic states will move north as a
warm front Tuesday. A weak cold front will push through the area
early Wednesday. High pressure briefly returns Thursday followed
by another system Friday.

&&

.NEAR TERM /THROUGH TUESDAY/...
In spite of ample low level cloudiness, surface high pressure
resides from the Delmarva to the eastern North Carolina this
evening. There have been a few sprinkles across northern Maryland
and adjacent eastern West Virginia, but recent trends have been
declining. Will reposition slight chance PoPs to chance sprinkles.

In the bigger picture, overrunning and shortwave energy has been
better across Pennsylvania. Low pressure can be analyzed near St
Louis; the nearest organized rainfall is in the mid Ohio Valley.
Recent RAP/HRRR runs suggest this area, supported by a warm front,
won`t make it to the mountains til 12z...a little slower than
GFS/ECMWF. The evening RAOB dry above 650 mb, so it will take some
time for deep moisture to advance. Have scaled PoPs down for the
overnight hours.

Warm front and shortwave energy will lift northward toward the
area into Tuesday...with overrunning precipitation overspreading
the western zones early Tuesday. Rain chances increase rapidly
during the morning, and peak near midday. Upper-level energy
weakens as it approaches the area and it also skirts by to our
north, so expect greater precipitation totals across NY and PA.
Around here, generally less than a quarter of an inch, except in
upslope areas across the Allegheny Front where a half inch (to
locally three quarters of an inch) is possible.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY/...
While steadier rain ends by early evening Tuesday...scattered
showers remain possible until weak cold front pushes through the
area early Wednesday. Further...intense upper-level energy moves
over the region Wednesday...which could lead to at least some
isolated showers. Best chances for these would be across upslope
areas and near the Mason Dixon line. Otherwise...expect warm
weather with highs in the 50s to low 60s Wednesday.

Drying out everywhere late Wednesday as high pressure builds into
the area.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
High pressure over the region Thursday will slide to the East
Coast Thursday night. Dry conditions are expected with mild
temperatures.

A low pressure system over the western Ohio Valley will pivot
northeastward into the Lower Great Lakes region Friday into Friday
night. Some energy associated with this main low will push across
our region during the same time. Light to moderate rain will
gradually spread northeastward across the Shenandoah Valley early
Friday. Rain should reach the District of Columbia and surrounding
areas by Friday afternoon. Temperatures will remain mild with high
temperatures about 10 degrees above normal. Drier air will work its
way into our region from the west behind this wave low pressure
energy and escorted by high pressure building in from the Ohio
Valley.

Even though high pressure will be overhead Saturday into
Saturday night, a weak piece of energy could linger nearby
keeping clouds and perhaps a slight chance for rain showers in
the forecast later Saturday into Saturday night. Temperatures will
stay mild throughout the period. A separate area of high pressure
over New England could aid in the cloud cover as we look at an
onshore flow in the east and an upslope flow along the Blue Ridge
and in the Potomac Highlands.

High pressure will hang on Sunday and Sunday night as a low
pressure system develops and deepens over the Mississippi Valley.
This low could send additional energy into our region Sunday night,
bringing the chance of rain showers once again.

On Monday, the main low will try to pivot northeast, bringing a cold
front across the region. The threat for more rain showers exist
Monday with a continuation of mild temperatures.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
Trapped low level moisture have resulted in flight restrictions
across the terminals. MVFR has dominated, although there have been
periods of IFR, especially at CHO/MRB.

Trends will be worsening as rain approaches, mainly during the
overnight hours. By the morning push, anticipate widespread IFR,
with LIFR possible. Restrictions will be due more to lowering
ceilings vs vsbys, although vsbys will be affected by rainfall
during the daylight morning/midday hours. Improving conditions
anticipated late Tuesday into Wednesday as high pressure builds
toward the area.

VFR conditions Thursday and Thursday night. Winds northwest
becoming south 5 knots Thursday. Winds south becoming southeast
less than 5 knots.

&&

.MARINE...
Light winds expected through Tuesday. Wind gusts could approach
marginal small craft criteria Wednesday afternoon behind the cold
frontal passage. Winds subside late Wednesday as high pressure
builds into the area.

No marine hazards Thursday and Thursday night.

&&

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

&&

$$
SYNOPSIS...MSE
NEAR TERM...HTS/MSE
SHORT TERM...MSE
LONG TERM...KLW
AVIATION...HTS/MSE/KLW
MARINE...MSE/KLW



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