Area Forecast Discussion
Issued by NWS Sterling, VA

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359
FXUS61 KLWX 070230 AAA
AFDLWX

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

.SYNOPSIS...
Coastal low pressure will move away from the region tonight before
high pressure briefly returns Wednesday. A potent cold front will
pass through Thursday. Arctic high pressure builds overhead Friday
into the weekend.

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Precip is ending sooner than advertised by models. While there
could be some patchy light drizzle overnight, temps have risen
above freezing everywhere and both 00Z RAOBs from IAD and PIT
show that you have to go above 10 kft to see any sub-freezing air.
Main concern is for fog development overnight, but current obs
show vsbys still good in many places much better than suggested
by guidance. Have cancelled all warnings and advisories.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
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.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
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.&&

.AVIATION /20Z TUESDAY THROUGH SUNDAY/...
IFR/LIFR cigs possible overnight with 2-4SM vsbys.
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.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...

&&

.MARINE...
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
persist across the middle and lower portions of the Bay and lower
tidal potomac. SCA conditions will continue into Wednesday
afternoon.

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.

&&

.TIDES/COASTAL FLOODING...
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.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory until midnight EST tonight for ANZ531-536-
     538-539.
     Small Craft Advisory until 1 PM EST Wednesday for ANZ532>534-
     537-540>543.
     Small Craft Advisory until 3 AM EST Wednesday for ANZ530.

&&

$$
SYNOPSIS...LFR
NEAR TERM...LFR
SHORT TERM...HSK
LONG TERM...KLW
AVIATION...LFR/KLW
MARINE...LFR/KLW
TIDES/COASTAL FLOODING...LFR



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