Scientific Forecaster Discussion
Area forecast discussion...updated
National Weather Service Baltimore Maryland/Washington District of Columbia
349 PM EST Thursday Dec 12 2013
Arctic high pressure will build to our south tonight through Friday.
Low pressure will approach the area Saturday from the Tennessee
Valley before passing through the region Saturday night. High
pressure will build overhead Sunday through the early portion of
Near term /through Friday/...
update...cancelled the Small Craft Advisory for the waters. Most wind observation over the
waters at or below 15kt at this time...will continue to subside through the rest of
Arctic high pressure will continue to build overhead late this
afternoon...bringing dry and cold conditions despite sunshine. Maximum
temperatures will range from the teens in the mountains to the lower 30s
in central Virginia.
The high will build to our south tonight...but it should remain
close enough to allow for the atmosphere to decouple. Dry
conditions...light winds and mainly clear skies will allow for
radiational cooling. Therefore...it will turn out quite cold with
min temperatures ranging from the single digits in the mountains to the
teens and lower 20s across most other locations.
A southwest flow will develop Friday as high pressure remains to our
south. High and middle-level clouds will build in well ahead of the
next storm system...but there will be some sunshine along with dry
conditions. Maximum temperatures Friday will be a few degrees warmer compared
to Thursday...but still below climatology.
Short term /Friday night through Sunday/...
a split flow in the jet stream is expected with southern branch
energy over the Southern Plains Friday evening and northern branch
energy over the northern plains. The southern branch system will
track into the Tennessee Valley Friday night. The northern branch
system should not have much of an impact on our weather since it is
not expected to phase with the southern branch.
Warm and moist air associated with the southern system will overrun
the low-level cold air in place...causing increasing clouds. Much of
the night will be dry...but some snow is expected to break out
toward morning...especially across the Potomac Highlands into
The southern stream system will move into our region Saturday.
Surface low pressure will track into the Ohio Valley while coastal
low pressure develops near the North Carolina coast. Warm and moist
air will continue to overrun the surface cold air in
place...resulting in plenty of clouds along with precipitation.
There will be enough cold air for wintry precipitation. Most places
will start off as snow and sleet Saturday morning before warmer air
works its way into the storm system...causing precipitation to
change to freezing rain and rain Saturday afternoon and evening.
Accumulating snow is likely across much of the area...especially
across the north and west near the Mason-Dixon line where low-level
cold air will hang on the longest. Ice accumulation from freezing
rain is likely...especially near and west of the Blue Ridge
The low will begin to pull away from the area overnight Saturday and
any leftover precipitation will be light. However...upslope snow
showers are expected along and west of the Allegheny Front.
A dry northwest flow is expected behind the low Sunday. Most areas
will turn out dry...but upslope snow showers are likely along and
west of the Allegheny Front.
Long term /Sunday night through Thursday/...
cold breezy nwrly flow will fill in for Sunday evening and the
beginning of the workweek as low pressure moves off to the NE. 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 builds in from the south on Monday and then gets reinforcement
from Canadian high pressure for the middle of the week.
Aviation /21z Thursday through Tuesday/...
VFR conditions are expected through Friday. Low pressure will impact
the terminals with wintry precipitation Saturday that will change to
rain before ending Saturday night. IFR/subifr conditions are likely
Saturday into Saturday night. Drier air will move in Sunday from the
northwest as the low departs.
VFR visibilities are expected through the period after the low
pressure system departs the area Sunday evening.
another Small Craft Advisory is in effect for portions of the
waters ate tonight into Friday as high pressure builds to our
Low pressure will impact the waters Saturday with wintry
precipitation changing to rain. The low will move away from the
waters Sunday and a Small Craft Advisory may be needed for portions
of the waters during this time.
A Small Craft Advisory is likely as breezy nwrly flow fills in
behind a departing low Sunday afternoon through Monday night.
District of Columbia...none.
Maryland...Wind Chill Advisory from midnight tonight to 10 am EST Friday
Virginia...Wind Chill Advisory from midnight tonight to 10 am EST Friday
WV...Wind Chill Advisory from midnight tonight to 10 am EST Friday
Marine...Small Craft Advisory from midnight tonight to noon EST Friday