Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 280150
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
850 PM EST Mon Feb 27 2017

.SYNOPSIS...
A warm front will lift north across the area through Tuesday,
followed by a strong cold front late Wednesday and Wednesday
night. After a brief period of high pressure Thursday, an area
of weak low pressure will cross the region Friday.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
A weak upper-level disturbance will pass through late this
evening before moving offshore overnight. A few sprinkles are
possible late this evening...but with plenty of low-level dry
air in place most areas will end up dry.

Breaks in the clouds are expected overnight behind the departing
disturbance. High pressure will remain offshore...so a southerly
flow will allow for milder conditions compared to recent nights.
Lows will range from the upper 30s in portions of the Shenandoah
Valley into eastern West Virginia...to the mid 40s across
Washington and Baltimore into southern Maryland/central
Virginia.

Will have to watch for overrunning toward Tuesday morning. There
may be enough warm and moist air that overruns the cooler air at
the surface...resulting in a couple showers across southern
Maryland. Will leave the slight chance for showers across this
area.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/...
Strong warm air advection moves overhead Tuesday as the warm
front crosses the region. The day should start partly sunny but
see an increase in clouds through the day. Chances for showers
and possibly a few thunderstorms increase in the afternoon and
evening as ongoing activity moves in from the west. Temperatures
will rise into the 60s area-wide.

Showers and few thunderstorms Tuesday evening should wane
overnight. However, there will be continued chances for a few
showers/thunderstorms through the night with deep moist
southwest flow, marginal instability, and elevated mixed layer
moving overhead. Lows in the 50s to around 60F.

Significant weather day possible Wednesday. Deepening low
pressure center will be passing through the eastern Great Lakes
Tuesday night and into Wednesday with a trailing cold front
moving towards and through the Mid-Atlantic states later
Wednesday and into Wednesday night. Some morning
showers/thunderstorms may be ongoing across the area, mainly
north, but most of the activity will likely be associated with a
cold frontal passage later Wednesday afternoon and evening.
Temperatures will soar in the warm sector out ahead of the front
well into the 70s to around 80F with dew points in the 50s to
near 60F. This should help generate MLCAPE values into the
500-1000 J/KG range. At the same time, very strong southwest
flow will move overhead, with 0-6KM shear increasing to 60-70
knots. Equally impressive is the 850mb flow maxing out at about
50-60 knots. These factors will help set the stage for potential
severe weather late Wednesday and Wednesday evening ahead of the
cold front. The Storm Prediction Center has already placed our
region in a Slight Risk for severe thunderstorms.

After cold front passes, will see gusty northwest winds take
over later Wednesday night with falling temperatures. Some
upslope snow showers also possible late near the Allegheny
Front. Lows Wednesday night from the upper 30s to mid 40s.

&&

.LONG TERM /THURSDAY THROUGH MONDAY/...
Upslope snow showers over the Appalachian Mountains early Thursday.
Weak high pressure will move overhead Thursday afternoon and evening
before moving offshore Thursday night.

An upper level disturbance is expected to approach the region from
the Great Lakes and bring a chance for a little rain or snow
Friday.

An associated surface cold front will bring a re-inforcing shot of
colder air into the region Friday afternoon through Friday night. A
chance of lingering snow showers or sprinkles Friday night.
Temperatures will be seasonably chilly.

High pressure will build into the region Saturday through Sunday,
keeping dry conditions and chilly temperatures across the region.

As the high moves east late Sunday and Sunday night, a dry front is
expected to move through the area.

On Monday, high pressure will be south of us as a warm front pushes
northward helping to spread clouds and perhaps some sprinkles across
the region.

&&

.AVIATION /01Z TUESDAY THROUGH SATURDAY/...
VFR expected into Tuesday afternoon. Rain and sub-VFR threat
increases later Tuesday afternoon and evening. Gusty
thunderstorms with sub-VFR cigs and vis are also likely later
Wednesday and Wednesday night as a strong cold front passes.
Some thunderstorms may become strong to severe. Winds will be
increasing out of the south, light today, but steady and gusty
by Wednesday afternoon, then turn gusty from the NW after the
front passes Wednesday night.

VFR conditions expected Thursday and Thursday night. MVFR
conditions possible with a chance for a little rain or snow
Friday. VFR conditions then return for Friday night and Saturday.
Winds gusty out of the northwest early Thursday become west 5
to 10 knots Thursday night. Winds west 10 to 15 knots gusts 20
knots Friday, and turning back southerly Saturday.

&&

.MARINE...
Generally sub-SCA winds expected for tonight into Tuesday. SCA
goes into effect at 4 PM Tuesday as southerly winds increase
late in the day and overnight. Southerly winds increase further
Wednesday with gale conditions possible. In addition, there is
the potential for strong to severe thunderstorms late Wednesday
and Wednesday evening as a cold front crosses the region. Winds
then turn northwest Wednesday night with gale conditions
possibly continuing.

Gale conditions possible into Thursday morning will gradually
weaken through the day, with lighter winds Thursday night.
Small craft advisories possible again Friday. No marine hazards
Friday night and Saturday.

&&

.CLIMATE...
Another period of unseasonably warm weather is forecast to
culminate in near-record warmth ahead of a cold front late
Wednesday. Here is a list of record daily warm temperatures for
March 1st (Wednesday).

Site   Record High   Record Warm Low
DCA    80 (1976)     57 (1910)
BWI    80 (1972)     53 (1910)
IAD    77 (1972)     43 (1997/1987/1976)

Here are updated February and Winter records. A warm Tuesday
will ensure the warmest February at all three sites.

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 26th)
DCA: 47.4    BWI: 44.0    IAD: 44.8

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 the 26th)
DCA: 43.8    BWI: 40.4    IAD: 40.8

Driest Februaries (total precipitation)
   DCA           BWI           IAD
1. 0.35 (2009)   0.26 (2009)   0.25 (1978)
2. 0.42 (1978)   0.36 (2002)   0.35 (2009)
3. 0.47 (2002)   0.56 (1978)   0.46 (2002)
4. 0.62 (1901)   0.63 (1977)   0.49 (1977)
5. 0.66 (1977)   0.65 (1901)   0.68 (1968)

Feb 2017 (through the 26th)
DCA: 0.34    BWI: 1.21    IAD: 0.33

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 4 PM Tuesday to 6 AM EST Wednesday
     for ANZ530>543.

&&

$$
SYNOPSIS...BJL/MM
NEAR TERM...BJL/MM
SHORT TERM...MM
LONG TERM...KLW
AVIATION...BJL/MM/KLW
MARINE...BJL/MM/KLW
CLIMATE...LWX



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