Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
851 PM EST Wednesday Dec 11 2013
a reinforcing cold front will move through the area tonight.
Arctic high pressure will build in behind the front Thursday and
Friday. Low pressure will move across the area Saturday into
Sunday. High pressure then briefly builds for early next week.
Near term /through Thursday/...
temperatures across the area a mix of near-freezing and well below
freezing conditions. Dewpoints are not any easier to pin-down...W/
values in the teens only miles away from observation in the u20s. The
recent snow and ice...evaporation...light winds from decoupling...
and clear skies are making for this odd stratification of temperatures/relative humidity
A weak cold front on the way from the upper Midwest...sort of. The
boundary itself will generally move across the area over the next
several hours but the tail end (the southern end) will dissipate and
little-to-no precipitation will make it past the mountains patches of light
snow/flurries will slide from southeastern PA/northern WV into the central Appalachians
into the early morning hours. Just some passing middle clouds east of the
mountains into the predawn hours.
Winds will pick up a bit once the front moves through before
dawn...then the Post-frontal subsidence will keep a steady breeze
over the area well into the late morning hours on Thursday. The surge of
drier northwest winds into the region will not only allow temperatures to drop
back into the teens and 20s overnight...but keep the cold
conditions throughout the day even under ample sunshine tmrw. The
combination blustery conditions and cold temperatures will also cause
low wind chills overnight...espec across the Appalachians where Wind
Chill Advisory is in effect through early afternoon Thursday.
Short term /Thursday night through Friday/...
Arctic high pressure will build overhead Thursday night...bringing
more cold conditions. High pressure will move off to our south
Friday and low pressure will move through the southern Continental U.S.. dry
conditions will continue Friday and it will be cold...but not
quite as cold as Thursday. A Wind Chill Advisory may be needed for
portions of the Allegheny Highlands Thursday night into Friday.
Long term /Friday night through Wednesday/...
high pressure moves off the middle-Atlantic coast late Friday...with
return flow then ahead of the next system ejecting from the southern
rockies. Isentropic lift clouds the area up Friday night...with
chance probability of precipitation for snow in the western half of the County Warning Area for the late
night. The 12z European model (ecmwf) is now faster with precipitation late Friday
night...onset depends on moist flow over coming the dry
Categorical probability of precipitation late Saturday into Saturday
night. The initial surface low will track along the west side of the
Appalachians...so southerly low level flow should make this a wintry mix
case. A coastal low looks to develop as the upper trough axis
approaches late Saturday night. Thus a brief cold air damming
wedge may develop Saturday night...lengthening the time for wintry
p-types as opposed to a changeover to rain. A surface high will build
over New England Saturday...but as of now does not appear to wedge
in like the case from this past Sunday.
Precipitation will end from west to east across the County Warning Area Sunday morning
as the low moves off to the NE. Cold breezy nwrly flow will fill
in for Sunday and the beginning of the workweek. Upslope snow is
possible for areas along the Allegany front on Sunday...when wind
direction and upstream fetch will be most favorable. The rest of
the County Warning Area will be dry through the end of the period as high pressure
passes overhead Monday morning and remains in control through the
middle of the workweek.
Aviation /00z Thursday through Monday/...
VFR conditions expected through Friday. Northwest winds will gust
around 20 knots late tonight and Thursday.
Low pressure brings precipitation...a wintry mix generally changing over to
rain Saturday into Saturday night. IFR conds possible during any
precipitation. Generally southerly flow ahead of the cold front. Cold front
late Saturday night brings VFR conds and gusty west winds.
VFR conditions are expected during the early portion of next week.
a cold front will pass through the waters tonight. Behind the
front...gusty northwest winds late tonight through Thursday. A
Small Craft Advisory is in effect for the waters during this time.
High pressure will build overhead Thursday night before building
to our south Friday. Winds gusts will be close to Small Craft Advisory criteria
over the waters...but capped gusts around 15 knots for now due to
a weaker pressure gradient.
Southerly flow in advance of a cold front Saturday into Saturday night.
Westerly flow Post-frontal may warrant a Small Craft Advisory Sunday
across the waters.
A Small Craft Advisory is likely as breezy nwrly flow fills in
behind a departing low Sunday and Monday.
District of Columbia...none.
Maryland...Wind Chill Advisory from midnight tonight to 1 PM EST Thursday
Virginia...Wind Chill Advisory from midnight tonight to 1 PM EST Thursday
WV...Wind Chill Advisory from midnight tonight to 1 PM EST Thursday
Marine...Small Craft Advisory from midnight tonight to 6 PM EST
Thursday for anz530>543.