Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 210125

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
825 PM EST Mon Nov 20 2017

High pressure will build to our south through tonight. The high
will move offshore Tuesday and a cold front will pass through
Tuesday night into early Wednesday. High pressure will build
back overhead later Wednesday through Thanksgiving Day. The high
will build to our south for Friday and Saturday before a cold
front moves through Saturday night.


High pressure is adrift toward the western Atlantic to our south
this evening. Scattered high cirrus noted over the Ohio Valley
is moving east into the area. That coupled with a developing
low level jet will be less than ideal for radiational cooling
after midnight, but temperatures are falling quickly this
evening with low dew points and clear skies. Most places
outside the cities will likely tank early, then rebound late.
Lows will be below freezing where radiational cooling can get
going early, but the cities should have trouble falling much
below 40.


High pressure continues sliding east off the coast on Tuesday as
low pressure starts developing off the southeast coast late in
the day. Strong southerly to southwesterly flow will bring
warmer air north, so it will be breezy and somewhat milder, with
highs likely to top 60 in warmer locales. High clouds will be
thickening as the next series of shortwaves approaches, but
otherwise dry weather expected.

A lot of uncertainty remains regarding development and track of
coastal low Tuesday night. American models still keep the system
east of the region, with rain just scraping southern MD, while
EC brings rain up to I-95 and Canadian guidance spreads rain
across the entire CWA. Have tapered POPS gradually, with likely
in southern MD, chance along I-95 and slight chance near I-81
in response. With the milder air brought north on Tuesday, this
should be all rain across these regions. However, late at night
the cold front currently entering the northwestern Plains will
arrive, bringing colder air and showers along the Allegheny
Front, which are likely to change to snow before the night is
over. Lows will stay well above freezing east of I-81, but the
Allegheny Front will drop below late.

Cold front sweeps any rain east of the region early on
Wednesday, with a gusty northwest wind and ongoing cold
advection. Temps likely to not follow a normal diurnal trend,
perhaps steady or slowly falling during the afternoon, but
should not be as windy as Sunday. Otherwise, reasonable
travelling weather is expected for the day before THanksgiving.
Temps will be hovering near 50 much of the day along I-95,
cooler west.

High pressure builds east into the region Wednesday night, with
diminishing wind and a return of more widespread sub-freezing


High pressure will build into the region Thursday through
Friday night. Dry conditions with plenty of sun expected each
day and mainly clear skies each night. Despite the daytime sun,
temperatures each period will be about 5 to 15 degrees below
average with highs in the upper 40s to low 50 and lows in the
upper 20s to near 30. Thursday will be the colder of the two
days, with some moderation Friday as winds turn southwest.

A storm system over eastern Canada will bring a cold front
toward and across the mid-Atlantic Saturday and Saturday night.
There is a chance for a few rain showers along the Mason-Dixon
region Saturday with a chance of rain and snow showers in the
Appalachians and along the Mason-Dixon regions Saturday night.
Temperatures will be closer to normal Saturday.

A gusty northwest wind will usher in cold air into the region
Sunday. With that, a chance of snow showers are expected in the
Appalachian Mountains. Below average temperatures expected to
retake the region. High pressure will be in control on Monday.
Dry conditions with below average temperatures across the


Generally VFR through the TAF period. High pressure shifting
east overnight will set up a low level jet over the terminals by
early morning, so included a little low level wind shear in the
TAFs - it may last a bit longer than currently indicated.
Currently shown in BWI/IAD TAF (35-40 kts through 2000 feet)
but not DCA as surface winds here will be a few knots higher
thus shear a touch lower (but still non-zero, 25-30 kts through
2000 feet). After inversion breaks, should generally be a gusty
S-SSW wind perhaps up to 30 knots at times during the day. A
period of sub-VFR cigs and vis is possible Tuesday night
depending on track of a coastal low pressure - American models
are further east, while Canadian and European suites bring some
rain into the terminals overnight. Solidly VFR Wednesday-
Wednesday night with a gusty northwest wind of 20-30 knots
during the day, diminishing a bit at night.

VFR conditions Thursday through Friday night. Winds light and
variable Thursday and Thursday night. Winds northwest becoming
south around 10-15 knots Friday into Friday night.


Winds are in a bit of a lull right now but made no change to
going headlines as winds will slowly ramp up beneath a
developing low level jet tonight. SCA continues for Bay waters,
and starts up again on the more sheltered waters by early
Tuesday, with mixing expected to bring 20-30 knots gusts to the
surface before midday Tuesday. This low level jet may be
disrupted as a coastal low passes to the southeast Tuesday
night, so relax SCA headlines as we head through the night.
However, SCA likely to return Wednesday as another cold front
blows through early in the day. Winds may start to relax again
later Wednesday night.

No marine hazards Thursday-Thursday night. Winds light and
variable Thursday and Thursday night. Increasing winds from the
southwest Friday into Saturday ahead of the next cold front may
require more Small Craft Advisories.


MARINE...Small Craft Advisory from midnight tonight to midnight EST
     Tuesday night for ANZ531-539-542.
     Small Craft Advisory from 6 AM to 6 PM EST Tuesday for ANZ535-
     Small Craft Advisory until midnight EST Tuesday night for
     Small Craft Advisory from 6 AM Tuesday to midnight EST Tuesday
     night for ANZ530.


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