Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 201529

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1029 AM EST Tue Feb 20 2018

Southerly flow south of a warm front will bring near record
warmth to the region today and Wednesday. A cold front will
pass through Wednesday night into Thursday before stalling out
to our south Thursday night. The boundary will return north as a
warm front Friday into Saturday before a stronger cold front
passes through from the west on Sunday.


Warm front has dissolved and is reforming to the north as low
level inversion is rapidly mixing out. Clouds are quickly
dissipating and temperatures in the region are rising rapidly.

For the rest of today, south/southwest winds and very warm
temperatures will be the main story as highly anomalous upper
level ridge (heights 2-3 SD above climatology for Feb) sits
parked off of the southeast US coastline. 850 mb temperatures
will rise into the 13-15C range by this evening, which is very
rare territory for Feburary. Expecting high temperatures to
reach the 70s for most locations, except holding in the 60s in
northeast MD and along the Chesapeake Bay where clouds clear
last. Some locations west of the Blue Ridge will make a run at


Tonight, with plenty of low level moisture as dew points sit in
the 50s, some fog and low clouds become possible again.
Extremely mild conditions for this time of the year are expected
with lows in the 50s to locally near 60F.

Wednesday will be exceptionally warm again with another day of
highs in the 70s to locally near 80F. As a cold front
approaches from the northwest later in the day, some showers
become possible west of the Blue Ridge.

The cold front will push southward across the region Wednesday
night, with surface northerly flow taking over. Aloft, with the
strong ridge still positioned near the southeast US coastline,
southwest flow will continue. This combined with some energy
aloft, will set the stage for a day of rain and drizzle on
Thursday, with temperatures crashing back towards normal, with
daytime highs in the 40s/50s.


A boundary to our south will return north as a warm front Friday
and it will stall out near our area Friday night through
Saturday. Most of the area should remain north of the boundary low clouds along with chilly conditions are expected
with perhaps even some light rain and drizzle.

The boundary will likely move into the area Friday night and
hang around through Saturday night. There is high uncertainty
as to exactly where the boundary will be which means that there
is high uncertainty with the forecast. The boundary will
separate chilly marine air to the north vs unusually warm and
moist air to the south. It does look like there will be
shortwave energy passing through in the southwest flow rain is likely although it will probably not be
raining the whole time. Given the anomalously moist airmass in
place...moderate to locally heavy rain is possible.

A stronger cold front is still expected to pass through the area
later Sunday into Sunday night from the west. More showers are
likely ahead of the front. A few thunderstorms cannot be ruled
out either...depending on whether or not the previously
mentioned boundary is overhead or to our north. If it is to our
north...then the warm sector may provide enough instability for
some thunderstorms to develop.


Low clouds and fog have nearly finished mixing out. VFR is
expected through this evening with a southwest wind. Winds may
gust up to 25 knots this afternoon.

Additional low clouds and some fog are likely again tonight,
with potential for IFR returning, especially BWI/MTN/DCA/CHO.
Similar to today, these ceilings/visibilities will improve
through Wednesday morning with VFR by the afternoon.

As a cold front crosses Wednesday night with rain likely
Thursday, another period of sub-VFR is likely.

A boundary will approach from the south Friday as a warm front
and it will stall out nearby or just to our north Saturday
through Saturday night. Times of rain are likely along with
subVFR cigs/vsbys ahead of the boundary Friday. In
fact...IFR/subIFR conditions are likely during this time. SubVFR
conditions are likely Friday night and possible Saturday
depending on how far north the boundary makes it. Uncertainty in
the position of the boundary remains high at this time.


Southerly flow will increase by this afternoon and a Small
Craft Advisory is in effect. With warm air temperatures
expected over considerably cooler waters, the strongest gusts
will likely be observed along the shorelines. The same situation
will occur Wednesday and a SCA is in effect. Additional Small
Craft Advisories may become necessary on Thursday as well as
northerly winds increase behind a cold front.

A warm front will approach the waters from the south Friday and
it will stall out nearby later Friday night through Saturday
night. Confidence on where the boundary sets up remains low at
this time. If the boundary sets up to the north...then SCA wind
gusts are possible in the warm sector. However...the boundary
may remain just to the south as well which would mean lighter
winds but extended low clouds/fog. Times of rain are likely
regardless of the frontal postion Friday through Saturday night.


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

If the Wednesday calendar day low does not drop below 60
degrees, 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 1976.

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...None.Record warmth is possible behind the warm front later today
through WednesdayVA...None. WV...None. MARINE...Small Craft
Advisory until 8 PM EST this evening for ANZ530>543. Small Craft
Advisory from 9 AM to 6 PM EST Wednesday for ANZ530>543.


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