Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
644 PM EST Friday Nov 28 2014
high pressure will move overhead this evening before pushing off to
our east late tonight. A warm front will lift to the north late
tonight and a southerly flow will usher in milder conditions for
the weekend. A cold front will pass through the area Monday and
weak low pressure may impact the area Tuesday into Wednesday.
Near term /through Saturday/...
surface high pressure will continue to build overhead through this
evening. A stratocu deck along with a few snow showers along and
west of the Allegheny Front will dissipate late as high pressure
builds overhead. However...more high and middle-level clouds will
quickly build overhead this evening as shortwave energy passes
through in the northwest flow aloft.
The high will move off to the east late tonight and a weak warm
front will lift north through the region during this time. At the
same time...shortwave energy will be passing through with most of
the energy remaining to our north. Warm advection ahead of the
warm front along with the shortwave energy may be enough to
overcome the dry air in place for a few flurries and perhaps a
period of light snow for locations near the Mason-Dixon line. As
of now...it appears that with the best forcing remaining to our
north the accumulating snow is most likely to remain to our north.
However...a whitening of the ground cannot be ruled out late
tonight into early Saturday morning for locations near the Mason-
Dixon line. Min temperatures will be cold...ranging from the teens along
the Allegheny Front to the lower 30s in downtown Washington and
The warm front will continue to lift away from our region Saturday
to our north. Shortwave energy will also be focused to our north
as well. Therefore...any light snow or flurries early will
dissipate. A southerly flow behind the boundary and departing high
pressure over the Atlantic Ocean will combine with some sunshine
to bring milder conditions compared to recent days.
However...there will be broken deck of middle-level clouds overhead
keeping maximum temperatures below climatology. Maximum temperatures are forecast to range
from near 40 along the Mason-Dixon line to the upper 40s in
portions of central Virginia.
Short term /Saturday night through Sunday night/...
broad ridging over the eastern Continental U.S. Saturday night through Sunday
night with a warming trend bringing temperatures above normal.
Warm air advection will set up a persistent cloud layer in the
Lower Middle- level inversion. Almost all precipitation is expected to be
over the eastern Midwest to the Allegheny Front. Forcing west of the
area turns to convergence late Sunday as a cold front approaches
from the Great Lakes. Precipitation expected to be rain through the event
as thermal profiles exceed freezing below 800mb or so. Dry east of
the Allegheny Front with southwesterly/southerly flow 10 to 15 miles per hour maintained
through Saturday night in decent pressure gradient.
Last day of November will have southwesterly flow and above normal
temperatures middle to upper 50s for most inland areas...low 60s possible
in the southwestern half of the County Warning Area where cloud cover looks to be more
scattered. Cold front approaches from the west Sunday night.
Long term /Monday through Friday/...
a cold front will sink through the area late Monday. There is not
a lot of moisture with this front and most models only have
scattered showers. As such have capped probability of precipitation at chance Monday into
Monday night. Any residual moisture could result in upslope snow
showers along the western ridges overnight Monday night as the
Strong and cold high pressure moves by to the north Tuesday into
Tuesday night. Southerly return flow/isentropic lift sets up as the
aforementioned front /which will have stalled to the south/ returns
north as a warm front. At least light precipitation seems plausible
in this setup so have chance probability of precipitation Tuesday night as well. Kept it as
a generic rain/snow mix but other ptypes may come into play as well
as strong cold air damming signature is evident while warm air
overruns the cold air at the surface.
Warming trend continues Wednesday into Thursday as a cold front
approaches from the west bringing with it another chance of rain
showers later next week.
Aviation /00z Saturday through Wednesday/...
VFR conditions are expected through Saturday. However...a few
flurries cannot be ruled out across the northern terminals late
tonight into early Saturday. MVFR visibilities are possible in any
flurries. Gusts around 15 to 20 knots are expected Saturday
Broken Lower Middle-level ceilings prevail Saturday night through Sunday
night...periodic MVFR possible...VFR visibilities with dry weather.
Southwesterly/southerly 10-15 knots through Saturday night...continuing through Sunday
before slacking Sunday night.
Spotty sub-VFR possible Monday evening in isolated showers. SW flow at or below 10 kts Monday
becomes northwest around 10-20 kts gusting to 25 kts following frontal passage Monday
evening. VFR Tuesday west/ wind turning north 10-20 kts...then light and variable
wind Tuesday night into early Wednesday west/ sub-VFR likely in low ceilings/light
winds had diminished less than 15 kts across all waters as of the
23z ob. Therefore...Small Craft Advisory was allowed to expire...with no marine
headlines expected the remainder of tonight as high pressure builds
High pressure will move off to the east Saturday and southerly
winds will increase. A Small Craft Advisory remains in effect for
the waters Saturday afternoon.
Southwesterly flow becomes more southerly Saturday night with Small Craft Advisory for up to 25 knots
channeling up the main portion of the Bay and 20 knots for eastern
tributaries and lower tidal Potomac. 20 knots winds likely continue
into Sunday before the pressure gradient slackens.
Southwest wind become northwest and increase to 15-20 kts west/ gusts
to 25 kts Monday as a cold front sinks through the waters. Northerly
channeling could result in a continuation of wind gusts to Small
Craft Advisory levels for a time Tuesday over parts of the waters.
Winds become light and variable Tuesday night into Wednesday as a
warm front slowly lifts across the area.
District of Columbia...none.
Marine...Small Craft Advisory from noon Saturday to 6 am EST Sunday for
Small Craft Advisory from noon to 6 PM EST Saturday for anz535-