Area Forecast Discussion
Issued by NWS Sterling, VA

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409
FXUS61 KLWX 110903
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
403 AM EST Sun Dec 11 2016

.SYNOPSIS...
High pressure will move off the Mid-Atlantic coast today. A warm
front will move into and lift north tonight followed by a cold
front pushing east Monday. High pressure will briefly move over
the area Tuesday into early Wednesday before the next reinforcing
cold front arrives mid-week with Arctic air behind it.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure is over the Mid-Atlantic region this morning. Warm air
advection is occuring aloft and clouds have increased across the
region. Light radar echoes are apparent across the Ohio Valley and
Potomac Highlands however nothing has been reported across the LWX
outlook area. Low level dry air is in place and snow showers are
having a difficult time reaching the sfc. As activity moves eastward
light snow is possible across the northern Potomac Highlands early
this morning. Little to no accumulation is expected. The mid-level
warm front will move into PA by late morning and dry conditions are
expected across the region today. Cool conditions expected today as
clouds stick around with temps in the mid to upper 30s and 40s
across central VA/southern MD.

Warm air advection aloft continues tonight as high pressure moves
off the Mid-Atlantic coast. Temperatures will fall into the evening
however southerly flow is expected to increase and temperatures will
start to rise this evening and continue to rise into Monday morning.
A plume of moisture ahead of an advancing cold front will enter the
Appalachian region late tonight. Sub-freezing temperatures are
expected across portions of the Potomac Highlands as precipitation
moves into the region and freezing rain is expected. A brief period
of sleet is possible at onset. A freezing rain advisory has been
issued for these locations tonight through Monday morning.
Across the rest of the Highlands and Shenandoah Valley...less
confidence in sub-freezing temperatures and if precipitation will be
rain or freezing rain. Stronger southerly flow is expected to
increase east of the blue Ridge once precipitation arrives and
therefore rain is expected. A 50kt LLJ will be located across the
Mid-Atlantic by early Monday morning. Gusty winds are expected on
the ridges with some gusts approaching 45-50mph. Precipitation will
move across the region by 12z Monday and 0.25-0.5 of liquid is
expected.

&&

.SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
Rain will come to an end from west to east Monday. Temperatures will
continue to climb Monday and reach the 40s across much of the region
and 50s across Central VA. Temperatures will be slow to rise across
the Potomac Highlands especially the valleys. The freezing rain
advisory goes through 15z Monday for these locations.

High pressure will build into the region Monday night into Tuesday
and continue through Tuesday night. Temps will rise into the 40s on
Tuesday.

&&

.LONG TERM /WEDNESDAY THROUGH SATURDAY/...
The polar vortex over northern Ontario at the beginning of the
period slides across central Quebec then quickly into the Canadian
Maritimes on Friday. This feature gives us a brief, glancing blow
of arctic air Wednesday night through early Saturday morning, with
the coldest period of the week appears to be late Thursday into
Friday morning, when temperatures are expected to reach the lower
teens as far east as the Chesapake Bay.

After the cold dome of high pressure moves offshore on Friday,
then a low pressure system over the midwest will approach, tapping
Gulf of Mexico moisture into the region. The models have a lot of
variability at this moment, but with the frigid air mass in place
on Friday, the possibility of freezing or frozen precipitation on
Saturday looms.

&&

.AVIATION /09Z SUNDAY THROUGH THURSDAY/...
VFR conditions expected through tonight. Sub-VFR
conditions expected tonight and will continue into Monday morning as
rain moves across the terminals. There is a slight chance of -FZRA
at MRB late tonight. A strong jet at 2k feet is expected across most
of the terminals late tonight. LLWS is expected however there is
some uncertainity as to how much wind reaches the ground late
tonight. SW winds 10-15kts with gusts up to 25kts are possible at
IAD/DCA. -RA will end from west to east on Monday. VFR conditions
expected Monday night-Tuesday night.

VFR expected Wednesday through Friday, with possible impacts at
all terminals due to strong NW winds on Thursday.

&&

.MARINE...
High pressure will shift offshore this morning. Southerly flow
increases this afternoon, and a SCA is in effect for most of the MD
Chesapeake Bay and lower Potomac. Mixing is expected on the waters
tonight and into Monday morning. SCA is in effect through Monday
morning. Winds will diminish Monday afternoon/evening. as high
pressure moves overhead Monday night and Tuesday.

At a minimum, solid small craft conditions will exist with the
onset of the artic air mass Wednesday night through Thursday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Freezing Rain Advisory from 10 PM this evening to 10 AM EST
     Monday for MDZ003-501-502.
VA...Freezing Rain Advisory from 10 PM this evening to 10 AM EST
     Monday for VAZ028.
WV...Freezing Rain Advisory from 10 PM this evening to 10 AM EST
     Monday for WVZ050>052-503-504.
MARINE...Small Craft Advisory from 3 PM this afternoon to 6 AM EST
     Monday for ANZ531>534-537-539>543.

&&

$$
SYNOPSIS...Lee
NEAR TERM...HSK
SHORT TERM...HSK
LONG TERM...Lee
AVIATION...Lee/HSK
MARINE...Lee/HSK



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