Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
302 am EST sun Nov 29 2015
a cold front over central Virginia this morning will continue to
move off to the south this afternoon through tonight. The boundary
will stall out over the Carolinas Monday before retreating back to
the north as a warm front Tuesday. A cold front will pass through
the area from the west Wednesday and high pressure will return
for late in the week.
Near term /through tonight/...
a cold front is located over central Virginia this morning while
surface high pressure is building over Quebec. The cold front will
continue to drop to the south this morning. Warm and moist air
overrunning the surface cooler air advecting in will result in
plenty of clouds along with periods of rain and drizzle.
The cold front will move off to the south this afternoon and high
pressure will build toward New England during this time. There
should be enough dry air filtering in from the north for
precipitation to taper off across most locations. The one
exception will be across central Virginia into the Potomac
Highlands where overrunning may remain deep enough for light rain
and drizzle. Clouds should hang on for most place...even across
northern Maryland for much of the day. However...there may be some
breaks of sunshine toward sunset across northern Maryland.
High pressure will build over New England tonight and the cold
front will continue to drop south into the Carolinas. Drier air
from the north to northeast flow will keep most locations dry
tonight. Again...moisture will be tough to erode across central
Virginia into the Potomac Highlands so light rain and drizzle may
hang on across these areas. There should be breaks in the
clouds...especially across northern Maryland into the Baltimore
metropolitan area and perhaps the Washington metropolitan
area/northern Virginia. Colder conditions are expected tonight
with min temperatures ranging from the upper 20s and lower 30s across
northern Maryland to the upper 30s and lower 40s in central
Virginia and southern Maryland.
Short term /Monday through Tuesday/...
surface high pressure will move off the New England coast Monday
while low pressure develops over the plains. The boundary will
remain stalled out over the Carolinas during this time. Any breaks
in the clouds from drier air will be short lived Monday morning
since overrunning will increase due to the strengthening low over
the plains. Therefore...plenty of clouds are expected and rain
across central Virginia Monday morning will spread north and east
Monday afternoon across the rest of the area. Still some
divergence in guidance as to exactly how fast this occurs...but
most guidance is in agreement that light rain will return during
the afternoon hours for most areas.
The boundary over the Carolinas will slowly return as a warm front
Monday night through Tuesday while the low over the plains Monday
night moves into the Great Lakes on Tuesday. Widespread rain is
expected during this time along with low clouds and patchy fog.
Leaned toward the colder guidance for min temperatures Monday night and
maximum temperatures Tuesday...thinking that warm air will have a tough time
taking over since there will be weak coastal low pressure
developing off the Delaware-Maryland-Virginia during this time. Usually the pressure
falls associated with this keep the coastal front from making too
much progress inland.
One more thing to note. There may be enough cold air for rain to
freeze on some surfaces late Monday afternoon through Monday night
across western Allegany County. The NAM is the coldest guidance
which indicates this occurring while other guidance keeps surface
temperatures above freezing. The fact that only one model has it keeps
confidence low at this point...but looking at the airmass upstream
there is plenty of colder and drier air that should surge into our
area before rain overspreads later Monday into Monday night. An
upslope flow and insitu wetbulb cooling may offset any warm
advection during this time. Therefore...will allow for the chance
for freezing rain but with low confidence.
Long term /Tuesday night through Saturday/...
by 00z Wednesday...the aforementioned cold front is generally noted
just west of the western edge of the County Warning Area...with the warm front
having lifted north of the Mason- Dixon...and the parent low over
the western gl region. On going rain showers ahead of the front
with incrsg moisture in the wake of the warm frontal passage and
reinforcing energy from embedded shortwaves aloft. No real
blocking mechanism aloft to slow the associated closed low...and
as such the 00z model guidance continues with timing similar to
previous runs of ushering the cold front through during the day Wednesday.
The colder air will lag...with a secondary front/trough bringing the
cold air advection Wednesday night.
Surface high pressure builds in the wake of the front the second half of
the week...with the center settling over the middle-Atlantic by Sat.
The models have now backed off from any precipitation mention Friday with the
high bringing about a much drier airmass.
Temperatures slightly above normal ahead of the frontal passage Tuesday night-Wednesday night.
With the arrival of the cold air advection late Wednesday night...combining with clearing
skies and weakening winds...should see temperatures dropping back to normal
levels Thursday into the weekend.
Aviation /08z Sunday through Thursday/...
a cold front will continue to drop to the south this morning. The
boundary has passed all the terminals but kcho. The boundary
should move through kcho between 12z and 14z. A north to
northeast flow behind the front has allowed for cooler air near
the surface to undercut the warmer air aloft...resulting in
periods of rain along with IFR/MVFR cigs/vsbys. These conditions
will continue through this morning. IFR conditions will overspread
kcho early this morning. Elsewhere...IFR conditions this morning
will gradually give way to MVFR conditions as drier air moves in
from the north. Drier air will continue to cause improving ceilings
this evening with most areas at VFR levels. Will hold onto
IFR/MVFR ceilings at kcho where the drier air will have less of an
More overrunning is expected Monday and low clouds will return.
IFR conditions are expected Monday night through most of Tuesday
along with periods of rain and drizzle.
Sub-VFR conditions likely...with IFR possible Tuesday night
into Wednesday morning ahead of the cold front. All precipitation during this time
will be rain with temperatures above freezing. Imprvg conditions to VFR as
the precipitation tapers off with the cold frontal passage. Southerly winds around 10 kts
becoming westerly Wednesday. Gusts 15-25 kts possible in the wake of the front Wednesday-
Thursday. VFR conditions with light winds Fri-Sat.
a cold front will continue to drop south of the waters today a
pressure surge tonight may cause winds to increase a bit. A Small
Craft Advisory is in effect for the middle portion of the Bay and
lower tidal Potomac River late tonight through Monday
morning...but it will be marginal. Reasoning for the Small Craft Advisory was
guidance showing 18-20 knots at the top of the mixing layer and
the fact that the mixing layer should be deeper over the waters
due to the relatively warmer waters.
The gradient will weaken later Monday through Tuesday. Winds will
remain below Small Craft Advisory criteria. Areas of fog are possible Monday
night and Tuesday along with periods of rain and drizzle.
Small Craft Advisory conditions possible Tuesday night into Wednesday ahead of the cold
front. Brief lull in the winds with the frontal passage...with
incrsg west winds in the wake Wednesday night and Thursday...more likely on
the Chesapeake Bay than Potomac River.
High pressure building in will bring conditions back to sub-Small Craft Advisory by
Thursday night...lasting into the weekend.
District of Columbia...none.
Marine...Small Craft Advisory from midnight tonight to noon EST Monday