Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 141838

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
138 PM EST Thu Dec 14 2017

High pressure will build overhead through tonight. Low pressure
will develop along the North Carolina coast Friday and move out
to sea Friday night. High pressure will return for Saturday
before weak low pressure impacts the area early next week.


Cold front has crossed the region with blustery northwest flow
occurring this afternoon area-wide. Strato-cumulus has been
gradually scattering out and diminishing, and this trend should
continue for the rest of the afternoon. At the same time, high
clouds will once again be increasing late in the day and
overnight in response to a developing jet max and next fast-
approaching system. Temperatures should still be able to fall
quite a bit overnight with lows in the teens and 20s.


Northern stream upper level trough will be quickly approaching
the region during the morning Friday. At the same time,
additional shortwave energy will be rapidly pushing eastward
from the lower Mississippi River Valley and across the
Appalachians by the afternoon. These two shortwaves are expected
to remain un-phased until well offshore, which will keep
any precipitation on the low side. That being said, surface low
pressure is expected to develop along the baroclinic zone left
by today`s frontal passage near the North Carolina coastline
Friday morning and move northeastward and offshore Friday
afternoon. This now looks like it will be just close enough,
when combined with the forcing from the northern stream trough
and intensifying jet max to bring some light snow to portions of
the region on Friday. Model differences still exist with
respect to westward extent, but the trends today have been for
high chances for our region.

Have increased snow probabilities to likely across portions of
southern Maryland and to chance as far west as the I-95 corridor
for late Friday morning, peaking in the afternoon, and ending
during the early evening. Have shown accumulations of less than
one inch for the Maryland counties that border the Chesapeake
Bay, going to a trace or less west of I-95. However, uncertainty
is still quite high at this time. Highs during the daytime
remain on the cold side, in the 30s area-wide.

Flow will turn northwest following the system`s departure Friday
night, with a brief period of upslope snow showers likely along
the Allegheny Front. Accumulations will be low though as
moisture will be quite shallow, up to about an inch of snow or
so. Lows Friday night in the 20s.

High pressure will then build in south of the region on
Saturday, with dry conditions expected. Highs Saturday in the
upper 30s to mid 40s and lows Saturday night in the 20s.


High pressure, centered to our south on Sunday,
will generate southerly flow over our region, allowing for high
temperatures to reach the mid to upper 40s for most of our CWA. A
shortwave trough will move across the area Sunday night into early
Monday. This will increase PoPs over our area, but still uncertain
how much QPF will be associated with it and any p-types.

Guidance suggests that mid to upper level energy could bring a
slight chance of precipitation  between Monday and Tuesday with
still above normal temperatures -reaching the 50s. A front could
bring a chance of precipitation Tuesday night into early Wednesday.
High pressure builds behind this front Wednesday into Thursday
bringing dry and more near-normal high temperatures.


Predominantly VFR conditions are expected through Saturday
night. Gusty northwest winds up to around 25 knots are expected
through today, diminishing by sunset. A period of light snow or
snow showers are possible across the eastern terminals later
Friday...but confidence is low at this time. This may bring a
period of reductions, with highest chances at DCA/BWI/MTN. High
pressure will then build in for Saturday.

Mainly VFR conditions expected early Sunday into Tuesday.
However periods of sub-VFR conditions are possible at times as
showers could move through the terminals.


SCA is in effect through the rest of the afternoon for all
waters with gusty northwest winds following the frontal passage
this morning. Winds will gradually lessen this evening and
tonight, but will likely remain gusty enough over much of the
Chesapeake Bay and lower tidal Potomac to keep SCA going until
midnight. Winds will then drop below SCA criteria later tonight
and remain that way through Friday as high pressure moves

Low pressure will then develop and move out to sea later
Friday. Gusty winds will develop behind the front Friday night
into Saturday. SCA goes into effect Friday night and may need to
be extended into Saturday.

Winds are expected to stay below small craft advisory threshold
Sunday into Tuesday. Winds could increase Tuesday night.


MARINE...Small Craft Advisory until midnight EST tonight for ANZ531>534-
     Small Craft Advisory from 8 PM Friday to 6 AM EST Saturday for
     Small Craft Advisory until 6 PM EST this evening for ANZ530-


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