Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 062000

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
300 PM EST Tue Dec 6 2016

Coastal low pressure impacts the area through tonight before high
pressure briefly returns Wednesday. A potent cold front will pass
through Thursday. Arctic high pressure builds overhead Friday into
the weekend.


Sfc high pressure is retreating to the northeast while low
pressure moves off the Carolina coast this afternoon. Strong
moisture advection has resulting in a large area of precipitation
across the region. Rain has been reported across the majority of
the area however...sub-freezing temperatures at higher elevations
has resulted in ice accumulation from sleet and freezing rain. The
greatest reports we have received were across the Allegheny Front
where one to two tenths of an inch of ice has been measured. This
is occuring above 1.5 feet with the greater ice amts above 2k
feet. A winter weather advisory continues until 7pm this evening
for the Allegheny Front...Blue Ridge Mountains and higher
elevations along the Shenandoah Valley and Potomac Highlands.
Further extension in time may be necessary especially along the
Allegheny Front.

A shortwave trough will move across the region this afternoon and
rain will end from SW To NE this evening. Low-level moisture will
stay in place tonight resulting in fog and potentially drizzle
through late tonight. Further ice accretion on surfaces may
continue after rain moves out across the Allegheny Front. Drier
air will eventually move into the region early Wednesday morning
when the coastal low moves out to sea and winds become NW.


Higher pressure will move into the Mid-Atlantic Wednesday and
mostly sunny conditions are expected. Temps will climb into the
40s n/w of the metros and 50s elsewhere.

A strong jet stream will be located over the Mid-Atlantic Wed night
into Thursday. A disturbance in the SW flow aloft will result in
clouds and showers Thursday morning. Rain or snow showers are
expected with the activity which will mostly stay south of DC and
near the Tidewater region of VA. Although sfc temps will be well
above freezing the warm layer may be shallow enough for snow
showers. It will likely be light and no accumulation is expected.

Mild weather will leave the Mid-Atlantic for awhile Thursday night
as an arctic front moves into the region. Temps will drop into the
20s across the region Thursday night. Wind chill values will also
drop into the teens/20s.

High pressure is expected to build in from the west Friday through
Saturday. This high will reinforce chilly air. An upslope flow
could generate snow showers in the Potomac Highlands.

The high will move to the East Coast Saturday night, before moving
offshore Sunday. Temperatures will remain chilly despite a return
flow evolving Sunday.

A storm system should move northeast across the Great Lakes
toward southeastern Canada Sunday night. A trailing cold front will
move across the region Sunday night, bringing a chance of rain or
snow showers. The 12z GFS model indicates that the frontal movement
to the east will be persistent and move to the East Coast waters
sometime on Monday. The 00z European model has a slightly different
outcome in which it pushes the front eastward a little slower and
stalls the front. Another storm system could develop along this
stalled front over the Tennessee Valley Monday. Here is where the
discrepancies lie.

Throughout the day Tuesday, the newly-formed storm system and
associated cold front should move across and east of the region.
Strong high pressure should build in behind the front, bringing very
chilly air into the region once again.&&

Cigs/Vsbys will deteriorate this afternoon/evening as rain
moves across the terminals. IFR/SubIFR conditions are expected
through this evening. Low-level moisture will continue overnight
and IFR conditions will likely persist into the early morning
hours of Wednesday. NW winds increase overnight and drying will
occur. VFR conditions are expected as high pressure builds
overhead. VFR conditions will continue Wednesday night.

Vfr conditions Friday and Friday night. Winds northwest 10 to 15
knots gusts 20 to 25 knots Friday. Winds west-northwest 5 to 10
knots gusts 15 knots Friday night.


Coastal low pressure will develop along the North Carolina coast
today. The gradient will continue to strengthen and a Small Craft
Advisory is in effect for middle portions of the Bay and the lower
Tidal Potomac River. The Small Craft Advisory continues through
this evening. A tight gradient from the coastal low will likely
presist across the middle and lower portions of the Bay and lower
tidal potomac. SCA conditions will continue into Wednesday

High pressure will approach for Wednesday and a northwest flow is
expected. Wind gusts around 20 knots are possible...but confidence
is too low at this time for a headline. Winds will become light
for Wednesday night.

Light winds across the waters through midday Thursday...before winds
increase above SCA criteria Thursday afternoon as cold front crosses
the waters. Solid SCA gusts continue Thursday night into Friday
morning. Increased mixing during the day Friday could lead to
marginal gale force winds...regardless...solid SCA will continue.
Winds drop back below SCA Saturday morning as large area of high
pressure builds overhead.


Persistent and strengthening easterly flow will lead to an
increase in tidal anomalies today. Action stage currently
forecast at the sensitive sites for this evenings high tide cycle
(e.g., Annapolis, Straits Point)...though marginal minor tidal
flooding is possible if anamolies are slightly higher than
currently forecast.


MD...Winter Weather Advisory until 7 PM EST this evening for MDZ501-
VA...Winter Weather Advisory until 7 PM EST this evening for VAZ503-
WV...Winter Weather Advisory until 7 PM EST this evening for WVZ050-
MARINE...Small Craft Advisory until 1 PM EST Wednesday for ANZ532>534-
     Small Craft Advisory until midnight EST tonight for ANZ531-538-


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