Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
257 PM EDT Monday Mar 10 2014
high pressure will settle over the Gulf Coast states today through
Tuesday. Low pressure and its associated cold front will pass
through later Wednesday into Wednesday night. High pressure will
build overhead Thursday before moving off the coast Friday.
Near term /through Tuesday night/...
a surface trough has formed across the Appalachians today as southwesterly
flow moves across the region. Wave clouds have been occurring all
day with a large wave cloud extending across the eastern half of the
County Warning Area. These clouds have been eroding on the west side of the cloud
shield. The northern Piedmont and along the I-95 corridor is 5-10 degree
colder than areas in full sun.
Middle to high level clouds will continue to stream across the northern half
of the County Warning Area this evening while disturbances move to the north.
Westerly winds aloft will increase tonight and 25-35kt gusty winds
will be possible along ridge tops and west of the Blue Ridge.
Westerly flow against the western slopes of the Allegheny Front will
result in overcast ceilings this evening which will not mix out
until Tuesday afternoon. A surface trough is likely to continue
through Tuesday afternoon as flow continues out of the SW. Warm air
advection is expected Tuesday and temperatures are expected to reach the
upper 50s low 60s near the Mason Dixon line to the low 70s in
central Virginia. Areas in valley locations such as Petersburg and Luray
will likely see close to 70 degrees as well. A disturbance will move
across PA Tuesday afternoon and middle level clouds will begin to
stream in from the northwest.
Low pressure will move into the middle west Tuesday night and moisture
advection from the Gulf will approach the middle Atlantic. Overrunning
will result in showers moving over the Potomac Highlands into
Short term /Wednesday through Thursday/...
a Stout 700-500 mb shortwave will approach the County Warning Area from the
west...accompanied by a coupled jet structure at 250 mb /the County Warning Area
will reside beneath both the right-entrance region of a 130 knot
northern stream jet streak and a 110 knot southern stream jet
streak/. This and strong baroclinicity between a warm and humid
airmass riding up the eastern Seaboard and another anomalously
cold Arctic airmass dropping down through the northern plains will
lead to a rapidly deepening surface low tracking from northern
Kentucky east-northeastward across northern West Virginia and
southern Pennsylvania during the day.
The County Warning Area will be solidly in the warm sector during the day...and with
low-level warm advection and cooling middle-upper level temperatures
with the approaching shortwave...the atmosphere will become
increasingly unstable through the day. Any breaks in the clouds will
lend to further surface heating and greater instability. Right now
model guidance depicts a ribbon of 300-800 j/kg along and
immediately ahead of a cold front accompanying the surface low.
Although these values are not usually very high...12-hour 500 mb
height falls in excess of 250 meters and strong synoptic forcing
with the middle-upper level trough will compensate to aid in upward
motion and the development of a line of convection along the front
Wednesday afternoon. Stronger winds associated with a 40-50 knot
925-850 mb low-level jet ahead of the front could be mixed down in
convection...with strong to isolated severe wind gusts possible
depending on the exact timing and evolution of showers and
thunderstorms along and ahead of the front. The strong southerly
winds ahead of the front may result in a coastal flood threat for
the high tide cycle late Wednesday afternoon as well.
A rapid drop in temperatures is forecast Wednesday evening behind
the front. 850 mb temperatures plummet to close to -20 c by 12z Thursday.
Precipitation will end across the County Warning Area before the colder air
arrives...however wind trajectories and an approaching secondary
shortwave will be favorable for upslope snow along the western
ridges for most of the night Wednesday night...where a few inches of
snow seems plausible despite shallow moisture/lift. A strong
pressure gradient between departing low and approaching high
pressure will result in gusty winds /which could approach advisory
level...especially west of the Blue Ridge/. Cold temperatures and winds
will lead to wind chill values from around 0 to -20 f Wednesday
night into Thursday morning west of I-95.
Cold temperatures persist Thursday into Thursday night but with
diminishing winds as high pressure moves overhead.
Long term /Thursday night through Monday/...
sunny skies will allow temperatures to rebound nicely Friday from
lows in the lower to middle 20s in the morning to highs in the 50s
during the daytime as high pressure over the southeastern US
stretches up into our area. Southwest flow will fill in as the high
moves off the Carolina coast Friday evening. Lows Saturday morning
will be in the 30s and high temperatures on Saturday afternoon should reach
into the upper 50s to lower 60s.
Low pressure located north of the Great Lakes will cause a weak cold
front to swing through the middle Atlantic Saturday night. Aside from
some light precipitation west of the Blue Ridge...local impacts should be
limited to increased cloud cover Saturday afternoon and a high
temperature on Sunday in the lower 50s...5 to 10 degrees cooler than
the high on Saturday.
An upper level disturbance will approach the area overnight
Sunday...bringing our best chances of precipitation in the period. Still
plenty of uncertainty in the forecast...but a wintry mix is possible
for some locations in the early morning hours on Monday before ptype
should switch over to light rain for the rest of the morning. Cool
air will fill in once again behind this front and high temperatures
on Monday will only get into the 40s.
Aviation /19z Monday through Saturday/...
VFR conditions are expected through Tuesday. Scattered-broken 10-15k
ceilings will occur during this period. Winds will increase at 2k
feet tonight and low level wind shear of 30-40kts from the northwest will be possible.
Sub-VFR conditions are expected in rain Wednesday with southerly
winds around 10 knots. VFR conditions are expected behind the front
with northwest winds increasing to around 20 knots with gusts 30-35
knots. Low-level wind shear is likely Wednesday into Wednesday night
amidst a strong low level jet both ahead of and behind a cold front.
SW winds 5 to 10 kts will continue across the waters through
Tuesday. High pressure will stay to our south during this time
period. Small Craft Advisory conditions are not expected during this time.
Small Craft Advisory conditions are likely Wednesday in gusty southerly winds ahead
of a cold front. Showers and thunderstorms could produce strong gale
force gusts Wednesday afternoon. Gale gusts are likely in a strong
northwest flow behind the front Wednesday night into Thursday.
A Small Craft Advisory may be necessary during the overnight
hours on Thursday and Friday.
District of Columbia...none.