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Area forecast discussion...updated 
National Weather Service Baltimore Maryland/Washington District of Columbia
551 am EST Mon Dec 5 2016

Synopsis...
high pressure will briefly build over the region today into
tonight. Coastal low pressure will impact the area Tuesday into
Tuesday night before high pressure briefly returns again for
Wednesday. A potent cold front will pass through Thursday and
Arctic high pressure will build overhead during the weekend.

&&

Near term /through tonight/...
the upper-level disturbance that brought the rain overnight will
move off to the east today while high pressure builds overhead
from the west. A northwest flow and subsidence behind the upper-
level disturbance will allow for increasing sunshine today and any
rainfall early this morning will quickly taper off. Max temps will
range from the 40s in the mountains to the middle 50s near
Washington and Baltimore.

High pressure will shift north and east toward New England tonight
while low pressure tracks through the Gulf Coast states into the
Tennessee Valley. Most of tonight will be dry...but clouds will
increase well ahead of this system. Precipitation will likely
move into the Potomac Highlands and central Virginia toward
daybreak. Low-level temps may be cold enough for sleet to mix in
with the rain...but surface temps should be above freezing for
most valley locations into central Virginia. Surface temps across
the Blue Ridge mountains and the Potomac Highlands may be cold
enough for freezing rain.

&&

Short term /Tuesday through Tuesday night/...
low pressure over the Tennessee Valley will Transfer its energy to
a coastal low Tuesday along the North Carolina coast. Warm and
moist air will overrun the surface colder air in place...resulting
in rain across the entire area. Cold air will remain wedged in
place so it will be quite chilly. In fact...evaporative cooling
at the onset of precipitation will cause low-level temps to drop
below freezing. The layer of cold air may cause sleet to mix in at
times...but surface temps across most of the valleys and east of
the Blue Ridge mountains should remain above freezing.

However...freezing rain is a concern for the Blue Ridge moutains
into the Allegheny and Potomac Highlands with most guidance
showing a layer of subfreezing air between about 1kft and and
5kft. Ice accumulations are likely across these areas and winter
headlines may be needed. For locations near the Mason-Dixon line
into the eastern West Virginia Panhandle...a period of snow and
sleet cannot be ruled out Tuesday morning. It appears that any
accumulation will be light and confined to grassy areas with
surface temps just above freezing.

The coastal low will gradually shift off to the east Tuesday
night. Precipitation will gradually end from southwest to
northeast.

&&

Long term /Wednesday through Sunday/...
coastal low will be moving off the NC/Virginia coast by Wednesday
morning...with high pressure beginning to build into the area.
This will effectively end precipitation chances across the
area...with the possible exception of some early morning showers
across NE Maryland and some light rain/snow showers across the Allegheny
Front. Remainder of Wednesday will feature dry weather with
seasonable afternoon highs.

Strong cold front crosses the area Thursday into Friday. High
intra-/inter-model spread remains with regards to timing...precip
type...and quantitative precipitation forecast. And...while most guidance shows only light quantitative precipitation forecast (if
any)...precip type/timing will ultimately determine the level of
impact.

What is certain is Artic high pressure building into the area
behind the front...likely bringing the coldest air of the season
to the region. Friday's highs will struggle to reach 40f (even in
the metros)...while areas west of the Blue Ridge will remain below
freezing the entire day. Very cold Friday into Saturday...with
lows in the 20s across much of the area.

Another cold day Saturday...as Arctic high pressure builds
overhead. Highs will again struggle to breach 40f. High begins
to move offshore Sunday...with a southerly wind component to
develop. This will allow for some slight airmass
modification...with temperatures back in the low 40s.

&&

Aviation /12z Monday through Friday/...
IFR cigs this morning should give way to VFR conditions as drier
air works its way into the area from west to east. Most areas
should clear out between 12z and 15z. Northwest winds are expected
late this morning through this afternoon wtih gusts around 15 to
20 knots expected. High pressure will cause light winds tonight.

Coastal low pressure will impact the terminals Tuesday into
Tuesday night. Rain and IFR conditions are expected to develop
Tuesday morning. Rain may mix with sleet at times...but little or
no accumulation is expected with surface temps above freezing.
Drier air may work its way in late Tuesday night as the coastal
low moves off to the east.

Any flight restrictions remaining early Wednesday will quickly ease
by early morning as high pressure builds into the area. Cold front
crosses the area Thursday into Friday...and while precipitation
amount/type is in question...gusty northwest winds are expected behind it
through early Saturday in strong cold air advection pattern.

&&

Marine...
winds will turn toward the northwest late this morning through
this afternoon as high pressure approaches from the west. A Small
Craft Advisory is in effect for the waters during this time...but
it will be marginal with gusts around 15 to 20 knots. High
pressure will build overhead tonight before coastal low pressure
impacts the waters Tuesday. A Small Craft Advisory is in effect
for portions of the waters Tuesday afternoon.

While high pressure briefly builds into the waters
Wednesday...winds may gust near Small Craft Advisory criteria during period of
best mixing (i.E., Daytime). Strong cold front crosses Thursday
into Friday. Small Craft Advisory are certain behind the front through early
Saturday in the strong cold air advection pattern...with gale
warnings also possible for portions of the waters.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory from 9 am this morning to 5 PM EST this
afternoon for anz530>543.
Small Craft Advisory from noon to 6 PM EST Tuesday for
anz532>534-537-540>543.

&&

$$
Synopsis...bjl
near term...bjl
short term...bjl
long term...mm
aviation...bjl/mm
marine...bjl/mm

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