Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
929 am EST Friday Dec 13 2013
high pressure will move off the coast late today. Low pressure
will approach the area from the southwest late tonight and
Saturday then will pass through the region Saturday night. High
pressure will build overhead late Sunday through the early portion
of next week.
Near term /through Saturday/...
high pressure will build to our south today. A west-southwest flow
will allow for milder conditions compared to Thursday...but maximum
temperatures will be below climatology. Maximum temperatures will range from the 30s in
the mountains to the lower and middle 40s in central Virginia.
A cold front will approach from the Great Lakes tonight as high
pressure moves off the coast. The southern branch of the split flow
pattern and shortwave trough will move into the Mississippi Valley
tonight. A broad area of low pressure is expected to move into the
Tennessee Valley approaching the middle Atlantic. Strong moisture advection
will take place Saturday morning as isentropic lift enters SW
Virginia. Temperatures will be below freezing and once the column is
saturated snow is expected to move from SW to NE across the region.
High pressure will approach New England and winds will veer out of
the NE-east causing a wedge of cold air to form against the mountains north-NE
winds and dense cloud cover will only cause areas west of the Blue
Ridge to rise slightly. More of a easterly fetch is expected
elsewhere and the water will help increase temperatures slightly. Similar
to last weekend...a wedge of cold air will persist Saturday as
warmer air begins to nose in aloft. The further north in latitude
the less of an effect of the warm nose. Therefore...snow is expected
to change to ice pellets across the Blue Ridge and west before switching to
zr-ip. Snow will continue for areas near the Mason Dixon line and
Potomac Highlands Saturday. Across I-95 and
east...temperatures are expected to rise to a few degrees above 32
and snow will change to rain-ice pellets and then rain. A Winter Storm Watch is
in effect for zones near the Mason Dixon line since they have the
best potential for 5 inches or more of snow Saturday into Saturday
Short term /Saturday night through Sunday/...
still may have some snow/sleet near the Mason Dixon line Saturday
evening...but thermal changes should support most of the snow
shifting to the north...with a period of freezing rain then likely
across western and north central Maryland...the eastern West
Virginia Panhandle and into northern Virginia especially within the
Shenandoah Valley as a cold wedge is stubborn and surface
temperatures remain at or just below freezing. Some ice
accumulation is likely /after the snow/. How much ice occurs will
depend on when the changeover takes place. Further
east/southeast along and east of Interstate 95...rain will be the
primary p-type through much of the remainder of the event Saturday
Followed a blend of 21z/03z srefs and latest GFS/European model (ecmwf) for pops/wx.
With low pressure moving off the coast/accelerating northeast...this
would generally take precipitation east of the County Warning Area by sunrise on Sunday
except perhaps some snow showers on the western slopes of the
Potomac Highlands. Clouds are expected to hang tough however and
Sunday sky grids reflect a mostly cloudy forecast.
Long term /Sunday night through Thursday/...
high pressure builds in Sunday night into Monday for dry/cold
conditions. A cold front will move through on Tuesday. There will be
some clouds and perhaps even some snow showers/flurries across the
northwest County Warning Area...then high pressure is likely to return for the rest
of the week.
Aviation /15z Friday through Tuesday/...
VFR conditions expected today and tonight. Low pressure will
approach the region Saturday morning and snow is expected through
Sat afternoon before changing over to a wintry mix.
Snow or mixed precipitation is likely at mrb Saturday night...but
latest guidance points to mainly rain Saturday night at the
remainder of the terminals. Regardless of p-type...expect low
ceilings/visibilities with srefs pointing to high probs of IFR/LIFR conditions
until late Saturday night/early Sunday morning as low pressure
departs/precipitation ends. Gusty northwest winds are expected Sunday then
high pressure builds in for Monday.
a few 18kt gusts have been observed this morning. A Small Craft Advisory is in effect
until late morning before high pressure moves closer to the region.
Low pressure will approach the waters Saturday and rain is
expected /likely beginning as a period of snow before the
Will have to watch marginal Small Craft Advisory conditions up the Bay Saturday
night...then higher probability of Small Craft Advisory conditions occurs on Sunday
with northwest winds as low pressure accelerates offshore. High
pressure builds in for Monday.
District of Columbia...none.
Maryland...Winter Storm Watch from late tonight through late Saturday
night for mdz003>007-501-502.
Virginia...Winter Storm Watch from late tonight through late Saturday
night for vaz028.
WV...Winter Storm Watch from late tonight through late Saturday
night for wvz050>053-055-501>504.
Marine...Small Craft Advisory until noon EST today for anz530>534-537-