Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 231542

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1042 AM EST Thu Feb 23 2017

High pressure will remain centered off the Mid-Atlantic coast
through Friday. A cold front will pass through the area on
Saturday. High pressure builds over the area during the early
part of next week. Another cold front will move through the area
around the middle part of next week.


Quiet and warm weather through Friday. Note the threat for
thunderstorms and gusty winds Saturday afternoon. These may be
sub-severe storms over land, but be particularly dangerous over
the waters.

As of 10am, low clouds/fog have mixed out with light south winds
across the area. Very warm with highs reaching into the mid
70s. There will actually be sufficient instability (200-400 J/KG
of CAPE) for pop-up scattered showers and isolated
thunderstorms mainly between 20z- 02z over the nrn Shenandoah
valley, ern WV panhandle and north cntrl MD. Showers will
dissipate with loss of heating later in the evening. More low
clouds and/or fog tonight as area remains in warm sector.


500 mb ridge crests over the area around 00Z Sat with sfc temps
rising another 1-4F degs. An elevated mixed layer also advects
northward into the area keeping atmosphere capped. Won`t rule a
few spots hitting 80F. Very warm Fri night with record high
minimums likely. Fog not likely to be a problem as winds
strengthen, but low clouds still possible.

Attention then turns to sharp cold front fcst to move through
the area Sat. SPC DY3 Otlk now has entire area under marginal
risk. Simulated cloud imagery from GFS shows convection
remaining strong possibly severe as it moves across ern OH, wrn
PA, and wrn MD between 12Z-15Z then weakening/becoming
shallower after 15Z as it crosses the rest of the fcst area.
Based on this, it appears any severe threat would be confined to
morning hours as strongest forcing stays north over PA. Cdfnt
clears the Chesapeake Bay by 00Z Sun, then turning much cooler
and windy.


High pressure will be building overhead on Sunday. While temperature
departures will be some 15-20 degrees lower from Saturday, highs
will still be near or slightly above normal. Outlying areas could
fall below freezing Sunday night.

The remainder of the extended period becomes much more uncertain.
The upper level pattern will feature mean troughing in the western
US and a building ridge over Florida and the Caribbean. With fast
WSW flow aloft, any cold air intrusions are unlikely, with
temperatures likely remaining above normal for the remainder of the
forecast period.

The tricky part will be timing in shortwave troughs within the fast
flow, with the possibility of a front remaining somewhere near the
area. If the GFS low pressure solution arrives early enough Monday,
there could be a little wintry precipitation in the mountains, but
this is far from certain. Otherwise, the forecast will carry a low
chance of showers for each period due to the wide spread of model
solutions. There is a little better agreement on more substantial
troughing arriving late Wednesday or Thursday...which would
represent a more targeted opportunity for rainfall.


VFR until a cold front Saturday. Light south flow today through
Saturday morning. Sharp cdfnt to move through the area Sat with
showers and gusty shifting winds.

VFR with high pressure Sunday into Sunday night. There are a wide
range of model solutions regarding the timing and strength of the
next low pressure system arriving Monday (or later), thus confidence
on impacts is low.


Small craft advisory conditions likely Sat through Monday.
Showers/isolated thunderstorms and a cold front Sat afternoon
may require SMWs or a gale warning. Water temperatures are still
in the mid 40s, so Saturday afternoon weather looks to be
particularly dangerous.

Winds will likely diminish through the day Sunday as high pressure
moves into the area, but SCA conditions may continue for a time. The
high will quickly move offshore Monday, but models differ on how
strong southerly winds will become, depending on the strength of low
pressure to the west. Will mention possible SCA conditions in the
marine synopsis.


Temperatures Friday are expected to be at least the second
warmest day on record (behind Feb 24, 1985). High minimum
records are possible for Friday and less likely for Saturday due
to evening temperatures dropping behind a cold front.

Record high temperatures for February 24:
BWI 79F (1985)
DCA 78F (1985)
IAD 79F (1985)

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 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 22nd)
DCA: 45.5   BWI: 42.1   IAD: 42.7

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 21)
DCA: 43.0    BWI: 39.6    IAD: 39.9




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