Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 281458

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
958 AM EST Tue Feb 28 2017

A warm front will lift north across the area through today,
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.


It`s a mostly sunny start to the day for much of the region, but
as a warm front located over the Ohio Valley moves towards the
region, will see rapidly increasing clouds as well as increasing
chances for rain showers by later this afternoon.

Currently monitoring the progress of ongoing
showers/thunderstorms along the warm frontal boundary across
West Virginia/Ohio/Kentucky. NAM/HRRR seem to have the best
handle of its evolution this morning, and leaned towards their
solutions, while also slightly speeding up their arrival across
our region. Expecting the first showers to make their entrance
towards the Allegheny Front by noon-1pm, spreading eastward and
reaching the metros around 3-5pm. Forecast CAPE/Showalters
indicate that much of the initial activity should be plain rain
with no thunder activity, but some elevated instability does
work in later in the evening and overnight, so thunder chances
increase then.

Temperatures have already risen into the 50s, and highs in the
60s to around 70F prior to rain seem on track.

After the disturbance passes later tonight, the chance of
precipitation declines. Warm southerly flow and clouds will keep
temps elevated, with lows well into the 50s in most of the
area. Warmest spots may not fall below 60.


Wednesday is the big show. Very powerful cold front pushes in
from the west as low pressure slides past to our north, with a
strong upper level shortwave and considerable low level
instability (for March 1st, at least). There is a LOT of wind
aloft to tap into, with 850s 50 knots plus at times. Given this,
the SPC continues the slight risk for severe thunderstorms, with
damaging winds still expected to be biggest threat, though more
organized cells could bring hail. Some early sun should push
temps close to, if not past, 80 in parts of the region, aiding
the thunderstorm threat.

Timing is still a little uncertain, and some storms may linger
towards midnight. After that, quick drying and cooling takes
place on a gusty NW wind. Potential for some gusts up to 40 mph
behind the front late Wednesday night and Thursday. Pressure
gradient declines as we head thru the day Thursday so winds
should diminish later on. Highs will struggle to rebound much
with considerable cold advection. Then we have to watch the
clipper system which looks to push into the region later
Thursday night with a reinforcing shot of cold air to boot.
Right now guidance favors northern areas seeing any snow before
dawn on Friday, with lows much colder than recent days
supporting it.


Friday the Alberta clipper scoots east from the area in the morning
with the upper trough axis shifting east across the area late
morning through midday. Instability under this low looks to produce
snow streamers/showers/flurries over the area during daylight hours
Friday. Guidance consensus max temps still is in the 40s across the
area to around 50F well south of DC in gusty NWly flow. However,
with the 850mb temps around -10C, wet bulb zero temps are less than
1000ft (a critical level for snow/rain). Therefore, went for snow
exclusively for NWrn suburbs and rain or snow metro areas and south.

Downsloping plays an important role in snow streamers in NWly flow.
Elevation increases from the Laurel Ridge of PA south along the
Allegheny Front of MD/WV. Therefore, accumulating snow chances
generally decrease south from the Mason-Dixon line due to increased
downsloping. However, the narrow bands that develop can produce
localized accumulating snow wherever they set up. Above freezing
temperatures will limit impact.

Surface high pressure settles overhead Friday night, then shifts
south to the SErn CONUS with a warming trend Saturday through Monday.


VFR expected into early this afternoon. Showers and sub-VFR
potential increases later this 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. An Alberta
Clipper shifts east from the area Friday morning with a shot
for brief accumulating snow through the day Friday across the DC
metros. High pressure/tranquil and cold Friday night.


Generally sub-SCA winds expected for most of today. SCA goes
into effect at 4 PM as southerly winds increase late in the day
and overnight. Southerly winds increase further Wednesday with
gale conditions possible, but confidence is low so went with SCA
for now. 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 into
Thursday morning before winds subside Thursday afternoon and

An Alberta Clipper shifts east from the Chesapeake Bay region Friday
morning with a reinforcing shot of cold air through Friday and
another gale possible into Friday night.  High pressure overhead
Saturday with south flow and warming Sunday and Monday.


Another period of unseasonably warm weather is forecast to culminate
in near-record warmth ahead of a cold front that crosses the area
Wednesday evening. 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 DCA and IAD and probably a close new
record at BWI.

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 27th)
DCA: 47.3    BWI: 43.9    IAD: 44.6

Washington is on pace for the third warmest winter on record,
Baltimore will have a top 10 warmest winter, and this will be the
warmest winter on record for Dulles.

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 27th)
DCA: 43.7    BWI: 40.4    IAD: 40.7

This has been a very dry February. Showers and isolated
thunderstorms are expected this evening across the Baltimore-
Washington area, so rainfall before midnight will be added to these

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 27th)
DCA: 0.34    BWI: 1.21    IAD: 0.33


MARINE...Small Craft Advisory from 4 PM this afternoon to 6 PM EST
     Wednesday for ANZ530>543.


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