Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
843 PM EST Friday Nov 28 2014
high pressure will move east across the area tonight. A southerly
flow will usher in milder conditions for the weekend. A cold front
will pass through the area Monday with high pressure building
back in for the middle of the week.
Near term /through Saturday/...
upper level trough continuing to push off to the north and east
tonight with near zonal flow expected by Saturday morning.
Attention this evening is the possible very light snow
development...mainly over western and central Maryland and NE WV. 01z
water vapor imagery indicating shortwave riding the flow aloft
passing through Ohio and eventually through central PA. Observation and radar
reflectivity with this energy currently reporting light snow.
Question though on how intact it remains as it nears the County Warning Area. High
pressure building in at the surface has ushered in much drier
air...with dew pt depressions anywhere 10-15 degrees. The drier
air in place has thus far kept any of the precipitation fro making it much
farther than central WV. Mesoscale models suggestive of this trend and
with the precipitation staying to the north where the better forcing
is. However...as the high nudges east...southerly flow returns
which might inject in just enough moisture that combining with the
energy aloft could produce light snow. Have gone with mainly a dry
forecast for the first half of the night...with slight chance probability of precipitation
for the second half right along the Mason-Dixon line. Some
clearing tonight with a quick decrease in winds have allowed many
areas to already drop to below normal temperatures. Temperatures will moderate
more for the latter half of the night as middle level clouds move in
with shortwave along with warm air advection with the return flow.
By Saturday morning...the shortwave energy will be more focused to
our north. Therefore...any light snow or flurries early will
dissipate by middle morning. A southerly flow behind the 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 /01z Saturday through Wednesday/...
VFR conditions through Saturday. Brief period of MVFR ceilings possible at
kmrb late tonight. Light and vrb flow will increase from the S
aftr 13z Sat. Gusts mixing in by middle morning...start time could be
+/- 1 hour than in tafs.
Broken middle level ceilings Sat night-Sun night with periodic MVFR ceilings possible with
light precipitation. Any precipitation should be in the form of rain. S-SW flow
through the period.
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 vrb
wind Tuesday night into early Wednesday west/ sub-VFR likely in low ceilings/light
no marine headlines expected the remainder of tonight as high
pressure builds overhead...resulting in light winds less than 10
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-