Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 250151
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
851 PM EST Fri Feb 24 2017

.SYNOPSIS...
A cold front will approach the area tonight and cross the area
Saturday. High pressure will then build over the area Sunday
through early next week. A warm front will then lift north into
the area Tuesday followed by another cold front on Wednesday.

&&

.NEAR TERM /TONIGHT/...

Very mild conditions will continue with persistent southerly
flow and increasing low level moisture. This increasing moisture
may lead to the development of low stratus overnight and into
Saturday morning, especially from the DC metro eastward. There
may also be some areas of fog, with the best chances along and
near the Chesapeake Bay where cooler waters in the 40s interact
with low level dew points in the 50s. Elsewhere, southerly flow
should preclude widespread fog formation. Lows tonight generally
in the 50s.

&&

.SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...

A strong cold front will cross the region Saturday, noted by
sharp wind shift from the south to west-northwest and tight low
level temperature gradient (difference of around 12C at 925 mb).
In addition, will see temperatures surge again out ahead of the
front, although will be dependent on extent and dissipation
rate of any morning fog/stratus. Current forecast of 70s ahead
of the front combined with dew points in the 50s should yield
500-800 J/KG of MLCAPE. That combined with increasing uni-
directional 0-6KM shear of 50-60 knots will set the stage for a
high shear/low cape day.

Expecting a fine-line or squall of convection moving along the
front from west to east through the day, generally in the 10am-
4pm timeframe. These forecast CAPE/shear profiles combined with
the sharp front are favorable for at least a low-end severe
threat. The strongest winds (50kt+) are progged to be generally
700mb and above, so will need some height to the convection to
mix this down to the surface. In addition, the best upper level
forcing will be located north of the region across Pennsylvania.
Because of these factors, current thoughts are for more of a
widespread 30-40 knots with the line, with localized severe
gusts possible. The Storm Prediction Center has placed the Mid-
Atlantic states in a Marginal risk for severe thunderstorms.

Much cooler temperatures will crash in behind the front for
Saturday night with temperatures falling back into the 20s and
30s by Sunday morning. Gusts of 30-35 mph, possibly higher, are
likely behind the front Saturday evening. Will also see some
light upslope snow showers develop in the northwest flow.

Calmer and more seasonable conditions are expected for Sunday
and Sunday night as high pressure builds into the region. Highs
will be in the 40s to low 50s with lows in the 20s and 30s.

&&

.LONG TERM /MONDAY THROUGH FRIDAY/...
As high pressure moves offshore Monday, a warm frontal system
will move parallel to the Ohio Valley and push into the mid-
Atlantic Monday night. A chance of rain and snow showers are
possible with the storm system for Monday night with rain
showers continuing into Tuesday.

The system moves to the east coast Tuesday then offshore
Tuesday night. The next low pressure system will move across
the Great Lakes, dragging its associated cold front across the
Mid-Atlantic Wednesday into Wednesday night. There is a chance
for rain showers ahead of the front.

As the main trough of low pressure pivots across the region
Wednesday night into Thursday, cooler and drier air will follow
with high pressure building in from the west. Some upslope snow
showers could evolve as well through the day Thursday.

A reinforcing shot of colder air will move in behind a cold dry
front Friday, only to be followed by high pressure from the Midwest
U.S.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
The region will remain in the warm sector of a low pressure
system passing to the northwest tonight.

Clouds will increase tonight. Areas of low stratus and possibly
some patchy fog will develop overnight and persist into
Saturday morning. MVFR/IFR conditions likely. Strong cold front
will cross the area on Saturday, likely reaching the metros
during the afternoon. Thin line of gusty showers/embedded
thunderstorms likely (brief IFR possible) , followed by a
several hour period of potential 30+ kt westerly gusts. Winds
will subside through Sunday as high pressure builds in from the
west.

There is the potential for periods of MVFR conditions Monday
through Wednesday with chances of rain showers. Winds will be
generally out of the southwest.

&&

.MARINE...
Southerly flow 10-15 kt tonight with high pressure offshore and
low pressure moving toward Great Lakes. There may be a few
localized gusts to 20 knots this afternoon, mainly along the
shorelines. Areas of fog possible tonight and into Saturday
morning.

A Small Craft Advisory goes into effect at 10am Saturday for
increasing southerly flow ahead of an approaching cold front.
The front will bring a dramatic change in conditions during the
late afternoon to early evening. Line of gusty showers/possible
thunderstorms will mark sharp wind shift to west. There is
potential for strong to severe thunderstorms, so stay weather
aware if out on the waters tomorrow. Behind the front, gale
conditions are expected, and a gale warning is in effect. Winds
slowly taper into Sunday morning, although SCA likely continues
a good portion of Sunday. There should be a lull Sunday night
with high pressure moving across the area.

Periods of SCA conditions are possible in the Monday to
Wednesday timeframe with southerly winds ahead of an approaching
low pressure system.

&&

.CLIMATE...
Record high maximum temperatures for February 24 and 25:
BWI 79F (1985), 83F (1930)
DCA 78F (1985), 84F (1930)
IAD 79F (1985), 79F (2000)

Record high minimum temperatures for February 24 and 25:
BWI 55F (1985), 52F (1930)
DCA 52F (1975), 54F (1891)
IAD 53F (1985), 47F (2000)

Warmest temperatures ever observed in February
BWI 83F (2/25/1930)
DCA 84F (2/25/1930)
IAD 79F (2/25/2000, 2/24/1985)

Warmest Februaries (average temperature)
   DCA           BWI           IAD
1. 46.9 (1976)   44.0 (1976)   42.1 (1990)
2. 45.2 (1990)   43.9 (1949)   41.1 (1976)
3. 44.7 (1997)   43.3 (1890)   41.0 (1998)
4. 44.3 (2012)   42.7 (1932)   40.9 (2012)
5. 43.9 (1949)   42.6 (1909)   40.5 (1997)

Feb 2017 (through the 23rd)
DCA: 46.3    BWI: 43.0    IAD: 43.6

Warmest Winters (Dec 1-Feb 28/29)
   DCA              BWI              IAD
1. 44.7 (1931-32)   45.3 (1931-32)   40.0 (2011-12)
2. 44.3 (1889-90)   44.4 (1889-90)   39.7 (2001-02)
3. 43.3 (2011-12)   42.4 (1948-49)   39.4 (1997-98)
4. 43.2 (2001-02)   41.9 (1949-50)   39.0 (2015-16)
5. 42.8 (1949-50)   41.3 (1879-80)   38.3 (1990-91)

Winter 2016-17 (through Feb 23)
DCA: 43.4    BWI: 40.1    IAD: 40.4

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 10 AM to 2 PM EST Saturday for
     ANZ530>543.
     Small Craft Advisory from 1 AM to 6 AM EST Sunday for
     ANZ530>543.
     Gale Warning from 2 PM Saturday to 1 AM EST Sunday for
     ANZ530>543.

&&

$$
UPDATE...WOODY!
PREVIOUS...MJM/KLW/DFH/RCM


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