Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 141503

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1003 AM EST Tue Feb 14 2017

High pressure will move offshore this afternoon. A cold front
will pass through the region Wednesday. High pressure builds
overhead late in the week and into the first half of the
weekend. An upper level disturbance passes nearby Sunday.


Surface high pressure will continue to build offshore this
afternoon while an upper level disturbance passes through the
area. Some mid level and high clouds will continue to stream
across the region late this morning before there will be
partial clearing from northwest to southeast this afternoon.
Radar echos show some possible activity extending from the
Appalachian Front east to the Potomac River Basin. However,
recent observations on the ground reveal no precipitation. For
the time being, we will leave a slight chance to chance of a few
snow flurries mainly across the Virginia Piedmont to the
Rappahannock River Basin into early this afternoon. The best
chance for precipitation will be across the Potomac Highlands.
Any precipitation amounts will be light. Snow may coat the
ground for locations along and west of the Allegheny Front.

A southwest flow will allow for max temps to remain above
climo. However...should clouds hold on longer than expected then
max temps could be several degrees cooler than forecasted.

Low pressure in the northern stream of the jet will move
through eastern Canada tonight while the cold front associated
with this system approaches from the west. Low pressure in the
southern stream will track through the Gulf Coast States. Our
area will remain split in between these systems...but there
could be enough southern stream moisture for a period of rain
overnight across central Virginia into southern Maryland. Any
rain that does occur will be light. Also...a few snow showers
are possible near the Allegheny Front ahead of the cold front
but precipitation amounts across these areas will also be light.
More mild conditions are expected for this time of year due to
increasing cloud cover and a light southerly flow. Min temps
will range from the mid and upper 20s along the ridge tops of
the Allgheny Front to the mid and upper 30s near Washington and


The southern stream low will pass by well to our south Wednesday
morning...and a period of rain is possible across central
Virginia into southern Maryland. Light rain may make it as far
north as Washington DC...but confidence is low at this time. The
cold front associated with the northern stream system will pass
through during the afternoon. Blustery and seasonably chilly
conditions are expected behind the boundary for Wednesday
afternoon. Scattered snow showers are possible near the Allgheny
Front...but any accumulation will be confined to locations along
and west of the Front.

Low pressure will rapidly intensify near New England toward Nova
Scotia Wednesday night through Thursday while an upper-level
trough remains overhead. Blustery and chilly conditions are
expected thanks to the northwest flow behind the low. A few snow
showers are during this time...but accumulating snow will be
confined mainly for locations along and west of the Allegheny
Front due to an upslope flow.

High pressure will build overhead Thursday night. Dry and cold
conditions are expected. There may be an upper-level disturbance
that rotates around the departing upper-level trough Thursday
night. This could bring a period of light snow overnight...but
confidence is too low at this time to mention in the forecast.
Will continue to monitor.


Few changes to long term forecast from last night...with little
in the way of impactful weather on the horizon.

Westerly low-level flow remains through much of high
pressure slides to our south across the gulf states. This will
allow for some gradual airmass modification...with highs
returning to seasonable norms.

Warm air advection increases Friday into Saturday as high
pressure slides off to our SE and southwesterly return flow
redevelops. Hence, above normal temperatures Saturday with
M/U50s across the Mason-Dixon line and M/U60s south across
central VA.

Disorganized upper-level disturbance approaches Sunday. General
consensus is that it will pass just to our south. Regardless,
not expecting much in the way of impacts across our area.
Precipitation amounts very light...with WPCs 90th percentile
less than a tenth of an inch across most of the area (50th
percentile has no accumulation across much of the area).


VFR conditions continue through Thursday night. Southwest flow
will gust around 15 knots this afternoon before diminising this
evening. A cold front will pass through the terminals Wednesday.
Gusty northwest winds are expected behind the boundary through
Thursday with gusts around 20 to 30 knots possible. Winds will
diminish Thursday night as high pressure builds overhead.

VFR conditions expected Friday and into the weekend with high
pressure over the area.


High pressure will move off the coast this afternoon and a
south to southwest flow will develop and persist through
tonight. Wind gusts will be close to SCA criteria this afternoon
into tonight. The wind field is strong enough aloft underneath
the mixing layer for a few gusts around 20 knots...but
confidence is too low for a headline at this time since the
waters will be relatively cooler than the airmass during this
time. Southerly channeling is possible tonight...but the
gradient will be relatively weak.

A cold front will pass through the waters Wednesday and gusty
northwest winds will develop behind the boundary through
Thursday before gradually diminishing Thursday night. A Small
Craft Advisory is in effect for the waters Wednesday and will
likely be needed through Thursday. A Gale Warning may be needed
for portions of the Bay and lower Tidal Potomac River Wednesday
night into Thursday.

Relatively light winds expected Friday and into the weekend with
high pressure over the area.


Southerly flow will develop this afternoon and persist through
tonight. Wind speeds should be light...but this may be enough of
a push to combine with the water that is piled up to our south
from the previous strong offshore flow. Water levels may spike
up this afternoon into this evening...and minor tidal flooding
cannot be ruled out. CBOFS indicated minor tidal flooding with
the tide cycle later this afternoon into this evening while
other guidance is lower. Leaned toward the other guidance since
the flow will be light...but this will have to be monitored
throughout the day.


MARINE...Small Craft Advisory from 9 AM to 6 PM EST Wednesday for


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