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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
921 am EST Sat Dec 20 2014

Synopsis...
high pressure will persist through Sunday. Low pressure will
track up the middle-Atlantic coast late Monday. A strong cold front
will then pass through the area late Wednesday.

&&

Near term /through tonight/...
a shortwave will pass through the region today...causing high and
middle-level clouds while surface high pressure builds overhead.
Seasonably chilly conditions will continue...but the deep moisture
from this system is expected to remain to our south.
Therefore...most areas will turn out dry. A few flurries or
perhaps a period of light snow cannot be ruled out across central
Virginia into the Potomac Highlands...but little or no snow
accumulation is expected.

Multiple rounds of energy will pass over the middle-Atlantic through
tonight. Due to little forcing as the jet stream is further
south...dry conditions are expected through tonight. Subsidence
behind any vorticity maxes may lead to some clearing. Forecast min temperatures
should be in the upper 20s to low 30s in urban areas. Clearing may
result in temperatures dropping a few more degrees.

&&

Short term /Sunday through Monday/...
high pressure extends from New England down into the middle-Atlantic
Sunday. Models suggest a good deal of sunshine with maxima near
climatology.

High pressure edges a little east Sunday night into Monday...with
pressure pattern signaling some semblance of a wedge. At the same
time...southern stream shortwave energy is also forecast to move
northeast on Monday.

Result will be increasing/thickening clouds Sunday night but think
any precipitation will remain to the south through daybreak. Trend of the
models is to delay precipitation a little longer during the day Monday.
Leaned toward European model (ecmwf)/srefs for timing. But if precipitation arrives early
enough...Monday morning may see a wintry mix of precipitation particularly
Blue Ridge westward. Bulk of the precipitation Monday afternoon/evening
appears to be rain but a wintry mix including potential icing from
freezing rain may linger across the higher elevations of the Potomac
Highlands into Monday evening.

&&

Long term /Monday night through Friday/...
shortwave exits late Monday night...but The Wedge remains into
Tuesday and with low level moisture in place chance of rain or
drizzle continues.

Attention then turns to a deep/strong upper level trough sending
a cold front through late Wednesday. Decent low level jet and
plume of moisture are expected to be transported ahead of the
front on Wednesday...leading to showers. Maxima are expected to
be warm for this time of year and have trended maxima near 60 east
of the Blue Ridge for Wednesday.

Dynamic system moves away Wednesday night. Tight gradient and cold
advection bring a windy and cooler Christmas day...although maxima
may actually still be a few degrees above climatology.

&&

Aviation /14z Saturday through Wednesday/...
VFR conditions expected through tonight. High and middle-level clouds
are expected during this time. A few flurries cannot be ruled out
today...but most locations will be dry. Winds will be
light...generally around 5 knots or less. High pressure will
control the weather pattern for Sunday with VFR conditions and
light winds.

Developing wedge and area of low pressure will likely bring some
rain and at least MVFR conditions Monday. If precipitation arrives early
enough Monday morning...it may begin as a mix.

IFR or lower conditions are then expected Monday night into Tuesday
with wedge in place and areas of rain or drizzle. Strong cold front
follows late Wednesday with showers/possibly gusty winds.

&&

Marine...
high pressure will persist across the waters today and tonight. Northwest
winds 5-10kts are expected on the waters today and weaken further
into tonight.

High pressure over New England on Sunday moves offshore early in the
week. Small Craft Advisory conditions are possible in southerly flow ahead of a cold
front on Wednesday...then behind the front for Wednesday night and
Thursday.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...none.

&&

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

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