Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 220211
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
911 PM EST Sun Jan 21 2018

.SYNOPSIS...
High pressure will remain off the southeast coast through
Monday. A cold front will approach the area Monday night and
cross the area early Tuesday. This will be followed by another
area of high pressure for the second half of the work week.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
High pressure will remain extended from the Atlantic Ocean into
the Carolinas tonight. A southwest flow around the high will
usher in plenty of warm air for this time of year. Increased
moisture will accompany the warmer air and that will result in a
bkn to ovc deck of stratocu. Most of the time will be dry due to
little in the way of lift...but an isolated shower cannot be
ruled out. The best chance for showers will be along/west of the
Allegheny Front. Will continue with min temps forecast to be in
the lower to middle 40s for most locations...thinking the clouds
will keep temps up a bit compared to last night.

Patchy fog is also possible...but current thinking is that the
stratocu deck will prevent widespread fog from developing. Did
allow for fog in the river valleys and rural areas overnight.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
Southerly flow will increase on Monday with mild conditions
expected. Morning strato-cumulus will give way to a cirrus deck
by the afternoon. Highs will be able to break into the 60s
pretty much area-wide.

A cold front will approach the region Monday night, crossing the
area Tuesday morning. This will bring rain showers to the region
Monday night into Tuesday. As the front moves through, a period
of heavier rainfall, gusty winds, and perhaps a convective fine
line and a rumble of a thunder will move from west to east. Lows
Monday night will be quite mild with southerly flow and
increasing moisture, mainly in the 40s to low 50s. Temperatures
Tuesday will range from near 50F out in western areas where
front will pass first to the mid/upper 60s south/east. Areal-
average rainfall should average around a half inch of rain.

Cold air advection will begin in earnest behind the front for
late Tuesday and Tuesday night, with temperatures falling back
into the 20s/30s by Wednesday morning. Gusty west/northwest
winds are expected as well, and gusts may reach into the 40-50
mph range across the higher terrain. A Wind Advisory may be
necessary for those locations. Elsewhere, gusts in the 25-35 mph
range appear more likely. In addition, in the increasing
westerly flow, some upslope snow showers are likely along and
west of the Allegheny Front with a light accumulation possible.

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
The 21/12Z GEFS shows a weak short wave crossing the region
on Wednesday.  This will cause a chance of snow showers in the
favored upslope areas Wednesday through early Thursday, along with
the chance of flurries along and west of the Blue Ridge.
Daytime highs and nighttime lows will be normal Wednesday and Thursday.

GEFS H5 mean height rises begin early Thursday, and continue through
Saturday. This will produce an expansive meridional surface
high pressure system impacting the entire eastern U.S. seaboard
before moving offshore late Friday. Temperatures will be above
normal both Friday and Saturday, with increasing chances of
precipitation on Saturday.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
Predominantly VFR expected through Monday. A stratocu deck
around 4-6kt is expected through midday Monday before
dissipating from south to north. MVFR cigs cannot be ruled out
overnight but confidence is too low to mention in the TAFs at
this time. Patchy fog is possible as well...but again confidence
is too low for a mention in the forecast since the stratocu deck
will prevent some radiational cooling.

As a cold front then approaches and crosses Monday night into
Tuesday, lower ceilings and a period of rain and possibly a few
thunderstorms are likely. This will bring sub-VFR conditions to
the region. In addition, low level wind field will be increasing
and low level wind shear is expected. Gusty surface winds in a
potential rain squall are also possible Tuesday morning. VFR
will return Tuesday afternoon with gusty west/northwest winds
expected.

Low chances of sub-VFR conditions Wednesday through Friday,
with the chance of sub-VFR conditions late Saturday.

&&

.MARINE...
Sub-SCA winds expected through tonight. Southerly flow will be
increasing Monday, but cool waters with warmer air temperatures
should limit mixing, so have kept below SCA criteria for now.
Low level wind field then increases further Monday night into
Tuesday morning, and SCA is in effect Monday night. Gusty
showers and gale conditions are also possible as a cold front
crosses the region Tuesday morning. SCA conditions are expected
to continue Tuesday and Tuesday night with gusty northwest winds
developing.

Small Craft Advisories may be required post-frontal on Wednesday,
and then again on Saturday on strong southwest flow.

&&

.TIDES/COASTAL FLOODING...
Increasing southerly flow ahead of an approaching cold front
will cause water levels to increase Monday into Tuesday. Minor
coastal flooding is possible, especially during the midday high
tide cycles Tuesday if the cold front isn`t through by then.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 1 AM to 6 AM EST Tuesday for
     ANZ530>532-535-536-538>541.
     Small Craft Advisory from 7 PM Monday to 6 AM EST Tuesday for
     ANZ533-534-537-542-543.

&&

$$
SYNOPSIS...Lee
NEAR TERM...BJL/MM
SHORT TERM...MM
LONG TERM...Lee
AVIATION...BJL/MM/Lee
MARINE...BJL/MM/Lee
TIDES/COASTAL FLOODING...



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