Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
930 am EST Monday Dec 22 2014

Synopsis...
a weak area of low pressure will track up the middle-Atlantic coast
today into Tuesday. Stronger low pressure will push north along
the Appalachians on Wednesday...sending a cold front eastward
Wednesday night. Breezy conditions will follow the front on
Thursday...then high pressure will build back into the region to
close out the week.

&&

Near term /through tonight/...
low pressure will move up the middle-Atlantic coast today and tonight
while a surface ridge from high pressure over New England remains
overhead.

Warm and moist air will overrun the surface cold air in
place...causing plenty of clouds along with precipitation that
will continue to overspread the area from southwest to northeast.
Precipitation has already overspread central Virginia and it is
moving into the Washington metropolitan area. Temperatures remain
close to freezing with dewpoints in the 20s. Therefore...the
Freezing Rain Advisory has been extended northeast to include the
Washington metropolitan area. However...any ice near Interstate 95
will be light and confined mainly to elevated surfaces.

Temperatures are colder farther north and west...but timing of
precipitation is still uncertain with areas across the Potomac
Highlands likely ending up dry for most of today. This adds to the
uncertainty for freezing rain across these areas. Will continue
with a Freezing Rain Advisory across northern and central Virginia
where confidence is highest for precipitation and cold air to
intersect...causing ice accumulation from freezing rain.

Weak low pressure continues moves up the middle-Atlantic coast
tonight. Highest probability of precipitation will be closest to the Bay...lower in the
mountains. Much of the County Warning Area looks warm enough for primarily rain
tonight but there still may be pockets of sub-freezing air west of
the Blue Ridge and any rain or drizzle may freeze and advisory may
need to be extended into tonight for those areas.

&&

Short term /Tuesday through Wednesday night/...
in the wake of the low...mid-Atlantic remains in a wedge/light flow
regime on Tuesday therefore cloudy skies and the chance for light
rain or drizzle will continue. Temperatures should be warm enough
for just liquid precipitation.

While there is general synoptic agreement in the computer models
through the middle of the week...there is still quite a bit of
spread in the smaller scale features. Amplified upper level pattern
through the middle portion of the week. Trough over the central
Continental U.S. Will lift east...inducing cyclogenesis over the western Gulf
of Mexico Tuesday night. This low will ride up the western side of
the Appalachians...reaching central Quebec by Thursday.

A strong low level jet ahead of the deepening low will transport
moisture up the eastern Seaboard Tuesday night...bringing increasing
chances of rain. Temperatures drop little from tuesdays highs...so
no frozen precipitation concerns. While probably not continuously rainy
through the period...90-100 probability of precipitation are warranted...with moderate rain
possible at times. The nature may become more showery on
Wednesday...but not a compelling reason to break that out at this
time. 00z NAM/met guidance much cooler for highs on
Wednesday...likely due to a much weaker surface low than the global
models...which allows the cold pool to linger east of the mountains.
However...the other guidance of 60s may be a bit overdone...except
perhaps east of I-95. If this occurs...will also have to monitor for
the potential of strong wind gusts if convective elements develop.

The cold front trailing the low will push through Thursday
night...bringing an end to the precipitation except some possible upslope.
However with the warm start...it will take until late in the night
for the temperatures to drop cold enough to support any snow. All
told...impressive precipitable water values and a dynamic system could lead to
storm total rainfall in excess of an inch...especially east of the
mountains.

&&

Long term /Thursday through Sunday/...
Thursday will be breezy behind the front. Any upslope snow showers
should gradually come to an end. There will only be a glancing blow
of cold air advection...as high pressure will be building in from the southwest.
This high will remain over the southeast states through Saturday and
temperatures are expected to remain above normal. The next chance of
precipitation will arrive as the next trough approaches Saturday into
Sunday. Model solutions still differ quite a bit...so probability of precipitation remain
low. There will be potential for temperatures to cool back down
behind this system for the second part of the weekend.

&&

Aviation /15z Monday through Friday/...
precipitation is expected to spread north through early afternoon.
Period of light freezing rain/sleet is most likely at cho/iad and
possibly BWI. May be too warm at dca for freezing rain...but
initial period of sleet can/T be ruled out before turning to rain.
Expect conditions to drop into MVFR this afternoon...then likely
IFR or LIFR tonight and continuing into Tuesday.

Below-VFR ceilings will linger through Wednesday night. Visibility could drop
below VFR in heavier rain/showers at times from Tuesday night
through Wednesday night. Winds will shift from southerly to westerly
Wednesday night and could gust above 25 knots on Thursday. No
significant weather expected after Thursday evening.

&&

Marine...
weak low pressure moves off the middle-Atlantic coast tonight. Marginal
Small Craft Advisory expected on the lower portions of the waters this afternoon
otherwise winds below Small Craft Advisory through Tuesday.

A strong low pressure system will move through the region between
Tuesday and Wednesday night...bring moderate rain at times over the
waters. A Small Craft Advisory is likely Wednesday through Thursday...with the
strongest gusts expected on Thursday. Winds will diminish Thursday
night as high pressure builds in.

&&

Lwx watches/warnings/advisories...
District of Columbia...Freezing Rain Advisory until 6 PM EST this evening for dcz001.
Maryland...Freezing Rain Advisory until 6 PM EST this evening for mdz013-
014-503>506.
Virginia...Freezing Rain Advisory until 6 PM EST this evening for
vaz025>031-036>040-051>054-501>508.
Freezing Rain Advisory until noon EST today for vaz050-055-056.
WV...Freezing Rain Advisory until 6 PM EST this evening for wvz055-
505-506.
Marine...Small Craft Advisory until 6 PM EST this evening for anz534-
537-543.

&&

$$
Synopsis...ads
near term...bjl/bpp
short term...ads
long term...ads
aviation...bjl/ads/bpp
marine...bjl/ads/bpp

National Weather Service Glossary of Abbreviations