FXUS61 KLWX 211613

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1113 AM EST Wed Feb 21 2018

Southerly flow south of a warm front will bring near record
warmth to the region this afternoon. A cold front will pass
through tonight into Thursday before stalling out to our south
Thursday night. The boundary may return north as a warm front
Saturday before a stronger cold front passes through from the
west on Sunday. High pressure will return for early next week.


Exceptional warmth for late February is expected again today
with record high temperatures likely.

Most clouds have moved out/dissipated, with partly/mostly sunny
skies at present. With 925 mb temperatures progged to be even
slightly higher than on Tuesday, highs will likely be even a bit
warmer with widespread upper 70s to even some low 80s. If these
come to fruition, daily records will be set, and the all-time
February max temperatures may be approached or exceeded, with
Washington-Dulles having the highest chance (see Climate
section below).

A cold front moving through the Midwest this morning will then
approach the region later this afternoon, crossing the area
during the evening and overnight hours. Chances for rain showers
will increase from west to east during the afternoon hours, and
with the warmth and moisture, several hundred joules of CAPE
will likely develop, and some thunder or gusty showers are also
possible. The highest chances of rain showers will remain
north/west of the metro areas through the day, then push south
through the metros during the evening.


As the front sinks southward across the area during the overnight
hours, falling temperatures and lowering clouds are expected.
There may also be areas of light rain and showers, although
significant rainfall isn't expected during the overnight hours.
Towards morning as an area of low pressure moves along the
frontal zone through the Ohio Valley, more widespread rain will
likely approach parts of eastern WV and western MD. Temperatures
by morning will fall into the 40s/50s.

Thursday will feature low clouds, periods of rain, and drizzle as
the weak system passes by. The greatest forcing and most
significant rain will likely pass north of the area across
Pennsylvania, but the strong warm air advection over cool/moist
low levels should still lead to rain and drizzle across the
region. Temperatures not really expected to go far with daytime
highs similar to the morning lows, in the 40s/50s. In fact,
temperatures may be falling much of the day.

With a strong high pressure center still over northern New England
Thursday night, funnelling in cool northeast flow, and an
anomalously strong upper level ridge over the southeast US
providing warm southwest flow aloft, areas of light rain and
drizzle will persist Thursday night and into Friday morning. By
Friday afternoon, as the next wave of low pressure moves along
the stalled frontal zone, some areas may break into the warm
sector, but uncertainty on its position remains high. Will show
40s across northeast MD to upper 50s/low 60s south/west Friday


Low pressure will develop over the Rockies and central Plains
Saturday. This will cause a boundary to our south to retreat
north as a warm front. However...the boundary is likely to stall
over our CWA which makes for a tricky forecast. The ECMWF has
been consistent in keeping the boundary farther south over
central Virginia into extreme southern Maryland. The GFS is a
bit farther north closer to the Mason-Dixon Line. The boundary
will separate chilly marine air to the north vs more very warm
air to the south. Did tweak the forecast a bit closer to the
ECMWF based on the latest trends of the guidance which shows the
GFS edging a bit farther south with the boundary vs previous
runs. Certainty remains very low. Shortwave energy will pass
through in the southwest flow aloft...bringing the likelihood
for some rain. Highest confidence for rain is across the
northern portion of the CWA...where there is an increased chance
for overrunning ahead of the boundary and closer to the
shortwave energy. Max temps are forecast to range from the lower
to middle 50s north of the boundary to the mid and upper 60s
south of the boundary.

The low over the Rockies and Plains Saturday will track through
the Great Lakes Saturday night and into southern Canada Sunday.
The cold front associated with this system will approach the
area Saturday night into Sunday. This may cause the boundary
overhead to move farther north as a warm front. A period of
unusually warm conditions is likely during this time. An
increasing low-level jet and shortwave energy will bring the
chance for showers during this time as well. Again highest
confidence in precipitation will be across the northern CWA into
the Appalachian Mountains. The cold front associated with the
low will pass through Sunday afternoon. A few showers and
perhaps even a few thunderstorms will accompany the frontal

Will have to watch for the potential of heavy rain Saturday and
Sunday. We will have an anomalously moist airmass in place. As
of now it appears that the best chance for flooding from heavy
rain will be to our north later Saturday into Sunday where
forcing will be stronger. Will continue to monitor.

High pressure will return for early next week bringing drier and
more seasonable temperatures.


VFR and gusty southwest winds at all sites through the rest of
today. As a cold front approaches and crosses the region this
evening and tonight, rain showers and even an isolated
thunderstorm are possible, with best odds being at MRB, then
moving towards DCA/BWI/IAD later in the evening. Winds will
turn northerly behind the front, and low ceilings with MVFR
conditions are forecast develop by early Thursday morning.
MVFR/IFR conditions are then likely in low clouds, areas of
rain, and drizzle Thursday, Thursday night, and potentially
lasting into Friday.

A boundary will remain overhead Saturday before possibly
retreating as a warm front Saturday night into Sunday. IFR
conditions are likely on the north side of the boundary.
Certainty in the position of the boundary remains low at this
time. A cold front will pass through Sunday. A few showers and
thunderstorms are possible along and ahead of the cold front.


Southerly winds with SCA conditions across the waters today.
With warm air temperatures expected over considerably cooler
waters, the strongest gusts will likely be observed along the
shorelines. As a cold front crosses the region tonight, winds
will turn northerly behind the front, and now look more likely
to reach SCA criteria, so have raised one for the bay and
adjacent waters (except the Potomac) for after midnight.

A boundary will remain near the waters through Saturday before
possibly moving north as a warm front Saturday night into
Sunday. A Small Craft Advisory may be needed on the south side
of the boundary during this time. Confidence in the position of
the boundary remains low at this time. A stronger cold front
will pass through from the west Sunday. A few showers and
thunderstorms may accompany the frontal passage.


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

The all-time February highest maximums are:
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

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

Record warm daily minimum temperatures
Wed 2/21
DCA 51 (1954)
BWI 49 (1981)
IAD 45 (1981)


MARINE...Small Craft Advisory until 6 PM EST this evening for
Small Craft Advisory from midnight tonight to 6 PM EST
Thursday for ANZ530>534-537>543.


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