NWS Winter Weather Discussion
County Warning Area [CWA]: LWX
Regional NWS Weather Office: Baltimore/Washington DC, Virginia

Likely Snow or Ice Ranges and Start Times Snow or Ice Storm Fall Probabilities

Likely Snow or Ice Ranges and Start Most Likely Snow or Ice Storm Total Expect at Least this much Snow or Ice
Potential for this much Snow or Ice Likely Start Time of Winter Precipitation
Most Likely Ice Glaze
Most Likely Snow Fall Totals 1200Z Outlook
  
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 Forecast Disussion
Forecast Discussion

000
FXUS61 KLWX 210201
AFDLWX

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

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

&&

.NEAR TERM /THROUGH WEDNESDAY/...
Bermuda high remains in place this evening, with a warm front
well north of the area, extended east from low pressure near
Lake Huron. A very sharp cold front extends southwest from the
low. There`s enough gradient around the high that winds remain
somewhat elevated this evening, and temperatures are still in
the mid to upper 60s in many areas. Definitely not typical of 9
PM on February 20.

Southwesterly flow will continue through Wednesday as a cold
front approaches from the northwest and high pressure slowly
retreats off the coast, with a strong ridge aloft.

With high dew points in the 50s and some drop in winds, expect
some patchy fog, low clouds and even a little drizzle to
redevelop, mainly east of the Blue Ridge, but with highest
chances near the Bay. Stratus may rule over fog, especially
inland, as the gradient really won`t relax all night. Valleys
west of the Blue Ridge are more likely to decouple, although
most guidance isn`t keen on much fog. Otherwise, it will be
extremely mild, with lows in the 50s to near 60.

After low clouds/fog burn off on Wednesday, it will be
exceptionally warm again with another day of highs in the 70s to
low 80s. As a cold front approaches from the northwest later in
the day, some showers become possible west of the Blue Ridge,
but odds are not high. Increasing clouds from the west during
the afternoon could limit insolation, keeping all-time February
records from being touched, but the potential for this does
exist. See climate section for details. In addition to the
warmth, it will be breezy again, with southwest winds
potentially gusting up to 30 mph.

&&

.SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY NIGHT/...
Cold front slide southeast into the CWA during the evening and
settles south of us by the overnight hours. Showers will be weak
and scattered at first, but as a wave of low pressure rides east
along the now stalled out front to our south, rain will become
more widespread on Thursday. As the wave passes east Thursday
night and cold high pressure passes by to our north, some chilly
air may make its way into the northern portions of the CWA which
might bring a risk of freezing rain. For now have held temps
just above freezing, but this potential will need to be re-
evaluated.

With the colder air moving in almost continuously from Wednesday
night through Thursday night, temperatures will be dropping or
steady just about the entire time, starting out in the 70s early
Wednesday evening, spending most of Thursday in the 50s and
40s, and then dropping into the 30s Thursday night.

&&

.LONG TERM /FRIDAY THROUGH TUESDAY/...
Cold air damming will be in place Fri with light rain and/or
drizzle as a warm front tries to lift through the area. There
will likely be a lull in precip Fri night into Sat behind warm
frontal passage with next chance of rain on Sat as a another
frontal zone associated with a stronger low over the mid MS
valley establishes across the area. Warm front might not be able
to clear the entire fcst area Sun before low pressure and
associated front become occluded Sun afternoon over Lk Huron.
The front should clear the fcst area by 00Z Mon at the latest
with a drying trend taking place early next week. Temps will
remain generally in the 50s with warm overnight lows due to
abundant cloud cover and high moisture content.

&&

.AVIATION /02Z WEDNESDAY THROUGH SUNDAY/...
VFR through this evening. Wind taking some time to abate (still
up to 14 kt at 9PM), and with a steady pressure gradient,
having the TAFS be more pessimistic in cigs than vsby seems the
most pertinent route to go. Low clouds/fog/drizzle may take
most of the night to spread northwest from their current
configuration. The highest likelihood for low cigs would be
BWI/MTN, followed by DCA, then IAD/CHO. There are many different
solutions pointing to a return of IFR cigs and MVFR vis, so
have gone that way with the TAFs. MRB may stay VFR cigs, but
could also see some dense fog develop if winds go calm. Most
guidance has shied away from such a solution though.

Low clouds/fog/drizzle should break within a few hours after
sunrise Wednesday morning and we turn out pretty much like
today, with VFR conditions and a gusty southwest wind, but
perhaps more mid level cloud.

Sub-VFR conditions possible at times on Wednesday night as a
cold front blows through and winds shift northerly. Sub-VFR is
more likely Thursday as a wave of low pressure brings some rain
to the region. Conditions may improve a bit Thursday night if
enough dry air works southward from high pressure to our north.

Possible flight restrictions Fri into Sat due cold air damming
signature and widespread precipitation.

&&

.MARINE...
Have expired the SCA this evening, although winds remain 10-15
kt in most locations. Expect this to continue through the night
with steady pressure gradient. Isolated gusts near SCA could
occur overnight. Winds likely ramp back up to SCA levels on
Wednesday so SCA goes back into effect mid morning through
afternoon. Cold front brings a wind shift Wednesday night, with
SCA possible on northerly flow in parts of the bay on Thursday.

SCA conditions possible Sunday into Monday with a passing wave
of low pressure and accompanying cold front.

&&

.CLIMATE...
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

In addition, its not out of the question that all-time February
maximum temperatures are tied or broken.

84 at DCA/Washington (2/25/1930)
83 at BWI/Baltimore (2/25/1930)
79 at IAD/Dulles (2/24/1985 and 2/25/2000)
- records only go back to 1960 at IAD

It goes without saying that daily records are in jeopardy. A
table of those records follows. Tuesday`s highs have already
been tied or broken, with BWI reaching 76, DCA 78, and IAD 77.

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)

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...Small Craft Advisory from 9 AM to 6 PM EST Wednesday for
     ANZ530>543.

&&

$$
SYNOPSIS...RCM
NEAR TERM...ADS/RCM
SHORT TERM...RCM
LONG TERM...LFR
AVIATION...ADS/RCM/LFR
MARINE...ADS/RCM/LFR
CLIMATE...LWX

Record Report from: NOAA-NWS
Script developed by: El Dorado Weather & modified by: SE Lincoln Weather