Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 130902
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
402 AM EST Fri Jan 13 2017

.SYNOPSIS...

A cold front is moving through the Mid Atlantic overnight. High
pressure will build into the area today...as a complex
frontal system develops across the Tennessee Valley Friday night.
The front is expected to push into the Carolinas Saturday. A warm
front is forecast to push through the region Monday. A cold front
will approach the area before weakening during midweek.


&&

.NEAR TERM /TODAY-TONIGHT/...

Freezing rain headlines discussed below in this section.

As of 330am, a 1043mb surface high is over western MN (well below
zero in the northern Great Plains and western Great Lakes) with a
1002mb surface low over the Gulf of St. Lawrence. All of this is
under a broad upper trough with a 150kt jet and north of an upper
level high centered over FL. A surface trough ahead of this upper
trough stretches from NYC to the central Shenandoah Valley as noted
by a thin line of light showers approaching Baltimore and DC. Lower
elevations are still in the mid to upper 50s with dewpoints in the
50s.

NW winds behind this front will bring in much drier air with
dewpoints expected in the 20s by this afternoon. Max temps mid to
upper 40s north in sunshine and low to mid 50s south under
decreasing clouds. By late tonight a 1040mb high will be over Ottawa
with a surface ridge extending south to the central Mid-Atlantic.
The front stalls to our south and returns north as a warm front this
evening as cold air damming sets up.

Warm air overriding this surface cold air is a recipe for a wintry
mix. East to west oriented bands of precipitation are expected to
develop tonight over portions of the area. These bands will maximize
precip and may cause a couple inches of snow on the cold side an an
ice glaze along and south. Overall QPF looks to be around a quarter
inch with locally more under the best bands. Given a warm start,
this will not be the most efficient freezing rain, so one to two
tenths Blue Ridge and west is a reasonable storm total ice for now.
For that, went with a freezing rain advisory Blue Ridge and west.
Some sleet could mix in, particularly at lower elevations where the
cold air is thicker, but the primary threat is freezing rain.

However, farther north, more snow and sleet warrants a winter
weather advisory. As of now, went just with Allegany County for this
advisory for wintry mix. Any freezing rain warrants an advisory, so
these headlines are expected to expand across most if not all of the
rest of the area starting either very late tonight or Saturday
morning. Cold air damming persists at least through Saturday over
the area, so wintry precip is expected for areas north of the wedge
front at least through Saturday. Precip chances look to decrease
Saturday night, but again any freezing rain or drizzle warrants an
advisory, so expect headlines through Saturday night if not into
Sunday.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY/...

SW winds on the highest ridges Saturday afternoon may bring the
temperature above freezing, but temperatures may drop back down
Saturday night, so for now went through Saturday with all headlines.

Lowered PoPs for Sunday though reinforcing high pressure may keep
the cold air damming in place, therefore did not remove the PoPs
completely.


&&

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...

The first part of the forecast is definitely the more challenging
portion. A warm front is expected to be pusing to the north Sunday
night. Wintry precipitation will be possible although it is too
early to pin down precip type.

After the front moves north of the region Tuesday-Thursday should
see a significant warm up as an upper level ridge builds over the
southeastern states Tuesday pushing high temperatures back into
the 50s.

A cold front will be positioned near the Appalachians Wednesday.
This would lead to a continued feed of warm air ahead of the front
along with chances for rain showers. Highs Wednesday look to
approach 60. The front is expected to push through the Mid
Atlantic but little in the way of cold air is expected for
Thursday. Highs still to be in the 55-60 range.

&&

.AVIATION /07Z FRIDAY THROUGH TUESDAY/...

VFR conditions through today with NW winds gusting around 20 knots.
Cold air damming sets up late tonight across the DC metros with
potential IFR cigs and a wintry mix developing after midnight if not
close to sunrise. This low condition and wintry threat continues
into Saturday night under the cold air damming wedge.


Sub-VFR conditions possible Sunday night as a warm front tracks
north through the Mid Atlantic bringing the potential for more
wintry weather. After the warm front moves north of the area VFR
conditions expected Monday and Tuesday.

&&

.MARINE...

Marine Cold front is moving through the waters early this morning
with NW winds expected to rise through the morning with around 20
knot gusts into this evening. SuB-SCA Onshore flow develops tonight
as a high pressure wedge develops and persists through Sunday.

Not expecting small craft advisory conditions Sunday night
through Tuesday.

&&

.CLIMATE...

Two record daily high temperatures were set for January 12th:
70 degrees at BWI (ties record for Baltimore area from 1890)
70 degrees at IAD (breaks record of 63 set in 1995)

Record daily warm low temperatures set for January 12th:
DCA (DC area): 51 degrees breaks the old record of 47 set in 1890
BWI (Baltimore area): 49 degrees breaks the old record set in 1890
IAD (Dulles area): 49 degrees breaks the old record of 41 set in 2013

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Winter Weather Advisory from midnight tonight to 6 PM EST
     Saturday for MDZ501-502.
VA...Freezing Rain Advisory from midnight tonight to 6 PM EST
     Saturday for VAZ025>031-504-507-508.
     Freezing Rain Advisory from 10 PM this evening to 6 PM EST
     Saturday for VAZ503.
WV...Freezing Rain Advisory from midnight tonight to 6 PM EST
     Saturday for WVZ050-055-502-504-506.
     Freezing Rain Advisory from 10 PM this evening to 6 PM EST
     Saturday for WVZ501-503-505.
MARINE...Small Craft Advisory from 8 AM this morning to 6 PM EST this
     evening for ANZ530>532-535-536-538>541.
     Small Craft Advisory from 8 AM this morning to 1 AM EST
     Saturday for ANZ533-534-537-542-543.

&&

$$
PRODUCTS...BAJ/WOODY!



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