Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 180835

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
335 AM EST Sun Feb 18 2018

High pressure builds into the region today and moves offshore
tonight. A warm front will lift northward through the area on
Monday, ushering in another round of unseasonably warm
temperatures. A cold front will approach during the middle
portion of the work week.


First note: holding on to the winter headlines in the higher
elevations for a little while longer. Traffic camera in
Frostburg does show light snow falling -- radar is overshooting
the echoes. This should be winding down before daybreak, and the
window for additional meaningful accumulation is almost over.

There is a bit of a slushy snowy mess left after yesterday`s
precipitation, and temperatures are at or below freezing
roughly north of a line from Cumberland to Harrisonburg to
Dulles to Baltimore. Some slick spots remain possible and
caution should be used, especially on that first step outside
and the first portion of any driving done early this morning.
Temperatures will be solidly above freezing by 9am everywhere,
ending any remaining issues.

Otherwise, no significant weather today with a good deal of
sunshine and highs approaching 50 except at the higher
elevations. Lows will remain above freezing tonight in many
areas as cloud cover increases and winds begin to shift out of
the southeast.


The new work week begins with a warm front swinging northward
through the area. Although I hate using a 50 PoP because it
feels like a hedging of bets, I`m looking at a pretty even mix
of model guidance that shows virtually nothing and guidance
that paints a period of light rain. Will keep likely PoPs west
of the Blue Ridge, where there`s just slightly more moisture
available. Regardless, I think we are talking about less than a
tenth of an inch of rain in most areas -- so nothing like the
precip events we`ve had recently. Can`t rule out a bit of light
lingering rain into Monday night, mainly near the Bay.
Temperatures Monday night probably don`t move much, and might
even perhaps rise slightly during the night.

Tuesday begins a two-day period of significant heat for mid-
February, reminiscent of the warm spell in the second half of
February last year. 00 UTC GFS MOS guidance is a jaw-dropper in
our western CWA and points west, giving Cumberland MD a high of
79 and Petersburg WV a high of 81. I`m not willing to go there
quite yet but it`s not out of the realm of possibility either.
The notable difference between this upcoming Tuesday and last
Thursday (which was similarly warm) is that it will be even more
humid. Given good model consensus on expected dewpoints and
wind, I think many places may struggle to drop below 60 Tuesday
night. I went several degrees above guidance, and my gut feeling
is I may still be on the cool side of reality.


An anomalously strong upper level ridge (heights 2-3 SD above
climatology for February) will be positioned near the southeastern
US coastline through the end of the week and into the weekend. This
will provide for strong and persistent southwest flow aloft and
continued bouts of moisture/warm air advection, which will lead to
an active period with above normal temperatures and precipitation

A cold front will be on the approach during the day Wednesday, and
models are beginning to form more of a consensus with frontal
passage likely late Wednesday or Wednesday night, and therefore
increasing chances for rain showers by Wednesday afternoon and
Wednesday night. Out ahead of the front, southwest flow and very
warm conditions are expected. After a morning start in the 50s to
around 60F, with 850mb temperatures progged to be from 12-14C and
925mb temperatures from 14-17C, widespread 70s are expected for
highs across the region. These temperatures will be in  (something that is
incredible for me to type)the realm of 25-30 degrees above
climatological normals for the day (49/32F at DCA).

As the front shifts southward Wednesday night and Thursday strong
high pressure will build into southeast Canada and New England. This
will create a cold air damming set-up across the Mid-Atlantic, as
low level northeasterly flow is overrun by continued southwest flow
and additional warm air advection aloft. This will create an
unsettled day weather-wise for Thursday with cloudy skies and rain
chances. Temperatures will be significantly cooler than Wednesday,
although still near or above daily normals.

The frontal zone will remain nearby through Friday and Saturday, and
current model guidance depicts the boundary surging back northward
with the region back in the warm sector by Saturday. But with the
zone still nearby, a wet and active pattern will be in place with
numerous chances for rain showers.


Dealing with low clouds and fog at the moment; these will be
gone by or after daybreak, leaving no further issues for
aviation through 18z Monday. Monday afternoon, there is a 50-60
percent chance of rain, and an even higher likelihood of
lowering ceilings, with MVFR likely and IFR possible. Sticking
with MVFR in the forecast for now. If the rain materializes,
visibility could be similarly restricted. Those restrictions
should improve as a warm front passes late in the day. Tuesday
will be extremely warm and a bit breezy, but dry.

Predominantly VFR expected Wednesday with gusty southwest flow.
Chances for showers will be on the increase by late Wednesday, and
periods of sub-VFR conditions become possible from Wednesday evening
through Thursday with rain and low cloud potential.


With high pressure moving overhead today, there will be no
marine concerns through Monday. As the high shifts offshore and
a warm front pushes through Monday afternoon (perhaps
accompanied by some light rain), southerly winds will pick up,
with gusts to SCA criteria possible Tuesday and Tuesday night.

Small Craft Advisories may be needed Wednesday with gusty southwest
winds. With warm air temperatures expected over considerably cooler
waters, the strongest gusts will likely be observed along the
shorelines. SCA potential continues into Thursday behind the frontal
boundary as well as winds turn to the north.


Some all-time February highest minimum temp records could be in
jeopardy, but it depends on how quickly the cold front moves
through Wednesday night.

If the Wednesday morning "low" that we are currently
forecasting ends up being the Wednesday calendar day low (60 at
DCA), it would be the first time not dropping below 60 at DCA in
February since 1891, and only the sixth time on record in the
entire meteorological winter season. Even a low 56 or higher at
DCA would be the warmest low in the month of February since

The all-time February highest minimums are:
61 at DCA/Washington (2/17/1891)
58 at BWI/Baltimore (2/17/1891)
55 at IAD/Dulles (2/17/1976)
- records only go back to 1960 at IAD

It almost goes without saying that daily records are in
jeopardy. A table of those records follows:

Record warm daily maximum temperatures
       Tue 2/20   Wed 2/21
DCA    76 (1930)  75 (1953)
BWI    76 (1930)  74 (1930)
IAD    70 (1971)  70 (1997)

Record warm daily minimum temperatures
       Tue 2/20   Wed 2/21
DCA    59 (1939)  51 (1954)
BWI    57 (1939)  49 (1981)
IAD    46 (1981)  45 (1981)


MD...Winter Weather Advisory until 5 AM EST early this morning for
VA...Winter Weather Advisory until 5 AM EST early this morning for
WV...Winter Weather Advisory until 5 AM EST early this morning for
     Winter Storm Warning until 5 AM EST early this morning for


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