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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
525 PM EST Tuesday Jan 27 2015

strong low pressure will continue to track northeast off the New
England coast into Wednesday. High pressure will build into the
Middle Atlantic States through Wednesday night. A cold front will
approach from the Ohio Valley Thursday...then pass across the
region Thursday night. High pressure returns Friday and remains
through Saturday night...before low pressure approaches region
late Sunday.


Near term /through Wednesday/...
having received a report of 1.75 inches of new snow today in Montana
storm and 3 inches farther west in Oakland...issued a Winter Weather
Advisory for the Potomac Highlands of WV/Maryland until 1 am.
Subsidence/drying should bring an end to the upslope snow later

Previous discussion...

Even though the intense surface coastal low is now over 500 miles to
the NE of our area...the larger upper level system still extends
back to the eastern edge of the upper Midwest. Along this edge remains
a relatively long/narrow but weak corridor of lift...pivoting and
swinging around the base of the upper level system over New
England. This region of lift has continued to develop batches of
flurries across portions of the area...namely the Blue Ridge and
surrounding counties on either side - up to the northern shen valley. This
feature is slowly dissipating across our area...W/ clouds showing
a fairly steady break-up across the region.

Temperatures have had plenty of trouble increasing today...between the
dense sun-blocking low stratus and the dry/gusty northwest winds. A few
locales around the area have found their way above the freezing
mark but west/ a northwest wind in the 15-25mph range...wind chills have
stayed well into the teens and 20s for most locations.

This theme will carry over into the nighttime hours as another round
of gusty winds will follow the dissipation of the cloud cover.
Ambient temperatures will have little trouble sliding well into the teens
for overnight lows. Add to that...winds gusts in the 20-30mph range
late tonight - wind chills in the single digits will be common.

The start of Wednesday will be met west/ clear skies and still
blustery conditions. Wind chill values around dawn will still be
in the single digits and teens. Although still quite cold...temperatures
will quickly jump back into the 20s and l30s by late morning. Not
enough time in the day however to get much above freezing...espec
west/ northwest winds continuing to gust in the 15-25mph range.


Short term /Wednesday night through Thursday night/...
ridging will move over the middle-Atlantic Wednesday night and surface high
pressure will become centered over the region. Temperatures will drop into
the teens as the region radiates overnight under calm and clear
conditions. A quick transition will occur Thursday morning as the
surface high moves off the coast and southerly flow moves into the
region ahead of a cold front. Warm air advection will move into the
region aloft with 850 temperatures going positive Thursday. The cold front
associated with a Great Lakes clipper will move across the Ohio
Valley Thursday morning. This will allow temperatures across most of the
middle-Atlantic to rise above freezing under southerly flow. Due to
snowcover across the northern portions of the outlook area...temperatures
near the Mason Dixon line should stay colder and barely reach
freezing Thursday afternoon. Temperatures further south will reach the middle
to upper 30s.

Disturbances ahead of the cold front will lead to precipitation to
move across the Allegheny Front and Potomac Highlands Thursday
afternoon. Forecast soundings depict a good amount of low level dry air as
the precipitation moves into the region. This should lead to light
precipitation to start as the column wetbulbs. Snow is expected to
begin across the western slopes and the Potomac Highlands Thursday
afternoon. As the cold front moves into the appalachian
region...light precipitation will move eastward and spread across most of
the middle-Atlantic staying snow near the Mason Dixon line and
rain/snow further south where temperatures will be warmer. All rain is
expected south of District of Columbia including the Piedmont...central foothills and
southern Maryland before changing to rain/snow as the wave of precipitation moves

Note for areas near freezing across the Mason Dixon line...saturation
should lead to a below freezing column but warm air advection aloft may lead to
sleet mixing in. Accumulations will be light ranging from 2-3
inches across the western slopes to 1-2 inches possible across
western Maryland. Less than an inch is expected further south.
Higher amounts across the western slopes are possible and an
advisory may be in the future for this area. Energy from an
amplifying upper level trough behind the cold front may lead to
flurries across the region into Friday.


Long term /Friday through Tuesday/...
both the 12z GFS and 12z European model (ecmwf) has a negative tilt 500 mb trough moving
across southern New England Friday night. This taps very cold 850 mb
temperatures at or below -14 across the entire County Warning Area Friday night...bringing single
digits west of the Blue Ridge and the teens to the metropolitan areas for
Friday night lows. Winds will continue strong on Friday night along
with low min temperatures likely producing advisory level wind chills at
least west of the Blue Ridge along with upslope snow showers.

Sat and Sat night see 500 mb hght rises and a bit of moderating Sunday has a deepening low approaching the County Warning Area from the
Tennessee Valley. The 12z European model (ecmwf) is a bit slower by 6 hours...but both
models have the same idea. With cold temperatures in place...this will
bring rain or snow likely Sunday afternoon and night. Monday will
see a reinforcing shot of colder air with 12z European model (ecmwf) temperatures once again
reaching at or below -14c by Tuesday morning...along with another good chance
of upslope snow showers.

Per the extended mex guidance through the long term...temperatures will be
generally below normal...with Saturday and Tuesday appearing to be
the coldest with both maximum and min temperatures about 10 degree below normal.
Saturday has the least chance of precipitation...and Monday night/Tuesday having the
greatest chance of precipitation.


Aviation /00z Wednesday through Sunday/...
a narrow band of flurries continues to center itself over the northern
Virginia Blue Ridge but is expected to dissipate before 00z. Winds
however will not dissipate in the coming hours...potentially
reaching a relative peak later tonight and into the early morning hours
as skies clear out. Still breezy out of the northwest on Wednesday but clear.

MVFR/IFR conditions are possible Thursday afternoon and evening as a
cold front crosses the terminals. Rain/snow is expected which may reduce
visibilities into Thursday evening.

Strong northwest wind gusts continues on Friday night with VFR.
MVFR conditions return to the terminals late Sunday followed by
another blast of northwest winds Monday and Monday night.


solid Small Craft Advisory conditions across the water today...staying the course
well into tonight and another period of breezy conditions on Wednesday
as well.

Southerly flow will increase across the waters Thursday and Thursday
evening and Small Craft Advisory will be possible. A cold front will cross the waters
by Friday morning and northwest winds will increase to S 20-30 kts with
gusts up to 45 kts on the waters. Gales will be likely Friday.

In the long term...gales will likely continue Friday night...then
return again on Monday and Monday night.


Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...Winter Weather Advisory until 1 am EST Wednesday for mdz501.
WV...Winter Weather Advisory until 1 am EST Wednesday for wvz501-
Marine...Small Craft Advisory until 6 PM EST Wednesday for anz530>543.


short term...has
long term...Lee

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