Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 220908 AAA

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
408 AM EST Sun Jan 22 2017

Low pressure will impact the area through Monday before moving
away Tuesday. A cold front will pass through the area Wednesday
into Wednesday night and an upper-level trough may build overhead
for the end of the week.


An upper-level disturbance will move away from the area early this
morning...but plenty of low-level moisture remains trapped
underneath the subsidence and nocturnal inversions.
Therefore...more low clouds along with areas of fog and drizzle
are expected through mid-morning. Fog will be dense in some
locations. A Dense Fog Advisory is in effect for northern and
central Maryland...northern Virginia and the eastern Panhandle of
West Virginia. Clouds and rain with the upper-level disturbance
has kept visibility just a bit higher farther south and east...but
visibility may decrease around sunrise as the upper-level
disturbance departs. A Dense Fog Advisory may be needed for these
areas...but confidence is too low at this time since the rain will
be clearing out close to sunrise.

Cutoff low pressure in the southern stream of the jet will track
through the Gulf Coast States later today before tracking
northeast into the Tennessee Valley and Carolinas tonight. A
strengthening gradient between this system and high pressure over
New England will allow for an easterly flow to develop and
strengthen later today. This will cause moisture to move in from
the Atlantic Ocean while at the same time warm and moist air from
the Gulf of Mexico will overrun the surface cooler air in place.
The overrunning will allow for more clouds along with periods of
rain. The best chance for rain will be this afternoon through
tonight when overrunning will be deepest. Rainfall amounts should
be light through this evening...since the bulk of the forcing from
the low will remain to our south.

However...moderate rain is expected to develop overnight as the
low-level jet strengthens in response to the approaching low. The
strengthening gradient will also cause windy
conditions...especially along the ridge tops and also across
north-central Maryland into the Washington and Baltimore
Metropolitan areas as well as southern Maryland. A Wind Advisory
may be needed for portions of these areas with frequent gusts
around 35 to 45 mph expected and gusts around 50 mph possible.


The low will slowly pass through our area Monday before tracking
to the north and east Monday night. A soaking rain is expected
to start Monday morning...but a dry slot will slowly move into
the area and this will decrease rainfall rates from south to north
later Monday morning into Monday afternoon. Gusty east to
northeast winds are expected Monday morning...but winds will
gradually diminish throughout the day as the low moves overhead
and the gradient subsides. The strongest winds are expected
through midday Monday across north-central Maryland into the
Washington and Baltimore Metropolitan areas and southern
Maryland...and perhaps across the Blue Ridge Mountains. A Wind
Advisory may be needed for portions of these areas.

Depending on the track of the low...the dry slot may be strong
enough for some breaks of sun to develop. The best chance for this
will be across southern Maryland into central Virginia.
Therefore...max temps will range from the 30s along the ridge tops
above the lower and middle 40s across northern the middle 50s across central Virginia. Confidence
in temperature forecast is low due to the uncertainty of how
strong the dry slot will be.

One other note is that with the upper-level low overhead...this
may cause enough dynamical cooling for rain to mix with snow
across the ridge tops of the Allegheny and Potomac Highlands.
Accumulating snow is possible across these areas...especially
above 3kft.

As the low slowly moves away from the area Monday night...wrap
around showers are likely across the area but rainfall rates will
be much lighter compared to late Sunday night and Monday morning.
Snow showers are possible along the ridge tops of the Allegheny
and Potomac Highlands mainly above 3kft.


Center of sfc low expected to be moving northeastward near/off the
Jersey coast by Tuesday morning...with a few lingering light
scattered wraparound showers mainly from DC and to the N/NE.
Upslope snow/rain showers could continue into mid-afternoon before
moisture becomes too shallow for quality ice crystal formation.
While rain will shift out of the area...breezy W/NW winds up to 20
kts and relatively warm conditions will remain Tuesday with drying
on W/NW flow. Heights rise over the area Tuesday into
Wednesday...ahead of next system. Unseasonably warm Wednesday with
highs in the U50s/L60s.

Cold front crosses the region Wednesday into Thursday...and, with
limited moisture east of the mountains, expect most areas to remain
dry. However, persistent upslope component through a saturated
layer should lead to prolonged upslope snow showers...of varying
intensity...Thursday afternoon through perhaps much of the
weekend...with some snow perhaps spilling east of the Allegheny
Front at times.

Main impact east of the Allegheny Front will be a drop in
temperatures back closer to seasonable averages Friday into the


Low clouds and area of dense fog will continue through mid-
morning along with occasional drizzle. LIFR to VLIFR conditions
are expected during this time. Cigs/vsbys will likely improve a
bit late this morning and afternoon...but IFR conditions will
persist. Periods of light rain will develop this afternoon through
this evening. A steadier rain is expected overnight into Monday.
IFR conditions are expected during this time.

Gusty east to northeast winds will develop overnight and persist
into Monday morning before slowly diminishing later Monday. This
is in response to low pressure moving overhead. Gusts around 30 to
40 knots are possible. A strong low-level jet is expected during
this time with east to northeast winds around 50-60 knots expected
around 2kft. This does pose a threat for low-level wind
shear...but will leave out of the forecast for now since gusty
winds are expected at this surface. This may cause more turbulence
instead of low-level wind shear. Low pressure will move away
from the area Monday night. Showers are still likely...but
cigs/vsbys may improve a bit more as the flow gradually turns to
the northwest.

Becoming mostly VFR by midday Tuesday as low pressure system moves
away...with only a few lingering light showers remaining.
Though, breezy conditions will continue with gusts 20-25
kts...before subsiding Tuesday night. VFR Wednesday with dry high pressure briefly nudges into the area. Weak
front moves through mostly dry Wednesday into Thursday with VFR


Low pressure will approach the waters through this evening. Winds
will gradually strengthen this afternoon through this evening. A
Small Craft Advisory is in effect for the Bay and lower Tidal
Potomac River this afternoon. will be marginal.
There is higher confidence in solid SCA conditions this evening as
winds continue to strengthen.

The pressure gradient will rapidly strengthen late tonight into
early Monday morning before gradually dissipating from south to
north later Monday. A Gale Warning is in effect for the waters
from late tonight through midday Monday. East to northeast winds
will gust around 35 to 40 knots during this time.

A Small Craft Advisory will likely be needed for portions of the
waters later Monday through Monday night as the low slowly moves
away from the area. Gusty NW winds exceeding SCA criteria remain
Tuesday behind departing low pressure system. Winds slacken late
Tuesday as influence from low wanes. Mostly dry cold front crosses
the waters late Wednesday into Thursday...with gusty winds
possibly to SCA criteria behind it Thursday afternoon.


Persistent easterly flow will increase the risk for minor tidal
flooding during high tide cycles beginning Monday afternoon and
lasting into early parts of Tuesday morning (especially at
Annapolis, Solomons, and Straits). Developing westerly flow should
allow for some decrease in anamolies later Tuesday.


MD...Dense Fog Advisory until 10 AM EST this morning for MDZ003>006-
VA...Dense Fog Advisory until 10 AM EST this morning for VAZ027>031-
WV...Dense Fog Advisory until 10 AM EST this morning for WVZ050>053-
MARINE...Small Craft Advisory from 6 PM this evening to 1 AM EST Monday
     for ANZ535-536.
     Gale Warning from 1 AM to 1 PM EST Monday for ANZ530>543.
     Small Craft Advisory from noon today to 1 AM EST Monday for


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