Scientific Forecaster Discussion
fxus61 klwx 191556
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
1056 am EST sun Nov 19 2017
a strong cold front is moving off to the east today and high
pressure will build to our south tonight through Monday night.
The high will move offshore Tuesday and a cold front will pass
through Tuesday night into Wednesday. Canadian high pressure
will build overhead later Wednesday through Thanksgiving day.
Coastal low pressure will likely move well out to sea Friday and
a cold front will pass through Saturday.
Near term /through tonight/...
deepening low pressure center over the St. Lawrence Valley will
track northeastward through the day reaching eastern Quebec by
Rain showers have changed to snow showers along and west of the
Allegheny Front as cold air rushed behind the cold front, and
upslope snow showers will persist through the day and into
tonight. The intensity and coverage of the upslope snow showers
will vary through the day, with the first heavy surge now over,
followed by a second surge between 4 PM and midnight tonight as
a potent upper level shortwave crosses the region and moisture
deepens again. A Winter Weather Advisory remains in effect for
western Grant and western Pendleton counties for 3-6" of snow.
The other main story for today will be gusty west/northwest
winds. As of this writing, it looks as though the best winds
were just after the cold frontal passage during the pressure
surge, and winds during the mid-late morning so far have been
lackluster by comparison. May take down advisory within the next
hour or so as winds are still expected to lessen further during
the afternoon and evening hours.
Temperatures today are not following the usual diurnal curve,
remaining steady or rising slightly through the daylight hours.
While climo day highs across the region are in the high 50s and
low 60s, the after sunrise highs should range in the 40s/50s,
locally near 60f south/east and in the 30s in the higher
A potent upper level shortwave and secondary cold front will
then cross the region late today into tonight. While passage
should be mainly dry, enough moisture and even a small amount of
instability may get picked up ahead of the front for a few
flurries/snow showers to make it downwind of the mountain chain
and into northwestern VA, the eastern Panhandle of WV, and into
Lows tonight in the 20s/30s.
Short term /Monday through Tuesday night/...
high pressure will build south of the region on Monday leading to
fair skies and dry weather. West/northwest winds in the morning
will lessen and turn southerly by days end. Highs Monday
within a few degrees of 50f.
Warm air advection and southwest flow returns for Monday night
and Tuesday ahead of the next northern stream shortwave.
Uneventful weather expected during this time with lows Monday
night in the 20s/30s and highs Tuesday warming back up through
the 50s and approaching 60f.
The shortwave is progged to cross the region Tuesday night with
the potential for some showers. As southern stream energy also
moves through the southeastern US, cyclogenesis does look to
take place off the coast of the Carolinas, but looks to stay
mainly S/east of the region at this point. As several models are
showing showers from this coastal system reaching back towards
I-95, did increase pops across the southeastern portion of the
County Warning Area.
Long term /Wednesday through Saturday/...
a cold front will move off to our south Wednesday while Canadian
high pressure approaches from the north and west. The high will
build overhead Wednesday night through Thanksgiving
day...bringing dry and chilly conditions.
Shortwave energy in the southern branch of the jetstream will
cause low pressure to develop over the Gulf of Mexico toward
Florida Thanksgiving day. The low is expected to track north and
east...but latest guidance continues to suggest that it will be
far enough out to sea so it has no impact on our weather. Will
continue to monitor trends in guidance over the next few days. A
northwest shift would have a significant impact on the forecast
for Friday. As of now...it appears that a return flow around a
departing surface high will bring somewhat milder conditions
along with some sunshine.
A cold front will approach Friday night before passing through
Saturday. Blustery and much colder conditions are expected
behind the cold front later Saturday and Sunday. Upslope snow
showers are possible along/west of the Allegheny Front. A few
flurries could even spill east of the mountains but confidence
is low at this time.
Aviation /16z Sunday through Thursday/...
main aviation weather concern through today will be gusty west
to northwesterly winds. West/northwest winds have been gusting
30-40 knots, but will gradually lessen during the afternoon
Otherwise, mainly VFR is expected through Tuesday. The next
chance of any precipitation and possible restrictions will
come Tuesday night with the next system.
High pressure will bring VFR conditions Wednesday through
Thanksgiving day. Coastal low pressure is expected to move out
to sea Friday so more VFR conditions are likely. However...the
track of this low will have to be monitored closely.
a Gale Warning remains in effect through today for all waters. Gusty
west/northwest winds with gusts to 30-40 knots will gradually
lessen during the afternoon hours.
Small craft advisories are then in place for tonight and into Monday
as northwest winds gradually abate. Sub-Small Craft Advisory winds are then expected
Monday night, before the next chance for Small Craft Advisory winds arrive on
Tuesday/Tuesday night ahead of the next system.
High pressure will build overhead Wednesday through Thanksgiving
day. A Small Craft Advisory may be needed for portions of the
waters Wednesday into Wednesday night. Still watching for the
potential of a coastal low Friday. As of now...it appears that
the track will be well out to sea so the most likely scenario is
for it to not have any impact.
strong offshore flow behind the front is causing anomalies to
sharply fall through this afternoon. Tidal blowout conditions
are possible tonight.
District of Columbia...Wind Advisory until 3 PM EST this afternoon for dcz001.
Maryland...Wind Advisory until 3 PM EST this afternoon for mdz003>006-011-
Virginia...Wind Advisory until 3 PM EST this afternoon for vaz025>031-040-
WV...Wind Advisory until 3 PM EST this afternoon for wvz050>053-055-
Winter Weather Advisory until 11 PM EST this evening for
Marine...Small Craft Advisory from 6 PM this evening to 6 PM EST Monday
Gale Warning until 6 PM EST this evening for anz530>543.
Small Craft Advisory from 6 PM this evening to 10 am EST
Monday for anz535-536.