Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
943 am EDT Wednesday Mar 12 2014
a strong low pressure center and its associated cold front will
pass through the Middle-Atlantic States this afternoon and evening.
An upper level trough will move across the area tonight...then
Canadian high pressure will build through Thursday night before
moving off the coast Friday. An upper level trough will persist
over the region this weekend...and a weak cold front will drop
through the middle Atlantic on Saturday.
Near term /until 6 PM this evening/...
we sometimes say the forecast has something for everyone. I think
we can take that literally at the moment...as this forecast has
almost every possible weather type/hazard...in the first 36 hours.
Strong to severe storms...snow...wind chills...strong winds...
unseasonably warm temperatures...unseasonably cold temperatures...potential fire
weather concerns...minor coastal flood potential...there is not
Surface analysis this morning shows low pressure just east of
Cincinnati moving eastward and deepening...now down to 989 mb.
Cloud cover has overspread the middle-Atlantic this morning...though
visible satellite does show some clear patches mainly west of the
Blue Ridge. The primary stationary front is to our north...which
will allow for moisture return today...but that moisture return is
being tempered by the departing southern stream trough...for now.
Once that is out of the way...low-level moisture will be able to
race in later today.
The surface low will continue to deepen as it moves eastward...moving
near or just north of the Mason-Dixon line. This keeps US in the
warm sector. Based on radar and hi-res models...the scenario for
today should be as follows...pre-frontal rain showers overspread the area
this morning into early afternoon. This will be followed by a
break in activity and then a line of convection developing along
the front. Some of the hi-res models hint at the convection
becoming more disorganized east of the Allegheny Front and then
organizing again east of the Blue Ridge. This is not an
800 mb winds increase to 40-50 kts even before any convective line
moves in...so even the prefrontal showers will have the potential
to mix down some gusty winds. The question for severe potential is
how much of a break occurs prior to the convective line...and how
much heating occurs during that time. Wind shear is extremely high
but how much instability will be realized is still significantly
in question at this hour. But the threat of damaging wind
gusts...both in a convective line and behind it with gradient
winds...is there. The shear lends itself to an isolated tornado
threat as well.
For the aforementioned reasons...high temperatures today are tricky. Did
not make many changes except to lower highs just a little bit in
The Highlands. Elsewhere...based on morning soundings...around or
even over 70 is easily attainable if clouds break.
Short term /6 PM this evening through 6 PM Thursday/...
cold front passes through the area late this afternoon...early
this afternoon...with a very strong pressure gradient building
around the back side of the low. Wind Advisory is up for almost
the entire forecast area for wind gusts 40-50 miles per hour. The area not
currently in the advisory will be very close to criteria and may
be added at almost any time.
The other thing that happens is a rapid drop in temperatures. By
03z tonight...The Highlands will be near 20 while areas near the
Bay could still be around 60. Lows tonight will ultimately be
40 to 50 degrees cooler than todays highs. With the gusty winds in
place...single digit wind chills can be expected late tonight...
with subzero wind chills in the Potomac Highlands. A Wind Chill
Advisory will likely be issued late this morning for affected
In terms of precipitation...most of the area will dry out
quickly...but upslope snow is expected over the Potomac Highlands.
Expecting a couple of inches of snow...but accumulations could be
higher if temperatures drop below freezing earlier than forecast.
Long term /Thursday night through Tuesday/...
there will still be a bit of a p-gradient Thursday evening as lopres mvs northeastward through
the Canadian Maritimes and hipres builds from the Ohio/Tennessee valleys...but expect
subsidence from the high /and dcplg/ to take over during the night. That
will be reflected by clear/calm overnight conds. Min-T guidance fairly uniform.
Went on the cooler end of that.
Not much to deal with on Friday either as hipres ridge ovhd...and center
of high engulfs the southeastern Continental U.S.. as lopres tracks across southern cnda...
the rtn flow does promote strong warm air advection. While the bulk of it will be north
of County warning forecast area...the effects will be tangible lclly as well. Took a model
blend...as do believe that a full temperature recovery will be a bit delayed
across northestern Maryland and along the Bay. Nonetheless...temperatures will be much closer
The aforementioned low will drop a weak cold front across the northestern Continental U.S. And
middle Atlantic Friday ngt-Sat. It will be outrunning most of its vorticity and northern
stream jet support...but it may get close to the lfq of a southern stream
jetmax Sat...so would prefer to not go west/ a dry forecast. Have 20-30 probability of precipitation...
which would mostly be rain showers expect for mountains where it would be cold enough for
shsn. Regardless...quantitative precipitation forecast light...and nothing of consequence. Canadian hipres
builds bhd the fnt Sat night and into Sun morning.
The xntdd forecast still looking quite murky. It would seem as though
cyclogenesis should occur somewhere along this boundary and track northeastward from
there...but guidance in real poor agreement on how this will transpire.
Acknowledged the potl presence of something in the database lt sun
into Monday night by raising probability of precipitation...but otherwise went pretty generic with
Aviation /13z Wednesday through Sunday/...
showers and thunderstorms will develop as a cold front approaches
during the afternoon. Potential for at least occasional IFR
conditions in heavy rain. Any storms or heavy showers will likely
be accompanied by gusty winds. Gusty northwest winds expected
overnight...possibly up to 50 miles per hour at all terminals...except kcho
where winds should not be quite as strong.
VFR Thursday with gusty winds northwest winds continuing...but gradually
diminishing during the day.
VFR should prevail through much of the outlook. Ceilings may flirt west/ MVFR
Sat in vicinity of weak cold front dropping across area.
southerly winds are on the increase...with small craft advisories
posted. Showers and possibly thunderstorms expected late this
afternoon or evening...with potential for special marine warnings.
Gales expected tonight under gusty northwest winds...gusts likely to
40kt. Gale Warning has been extended into Thursday for all of
Maryland Chesapeake Bay and the lower tidal Potomac.
P-gradient will still be present Thursday evening...and expect at least Small Craft Advisory will be
reqd at the start of the period...but gradient will relax through the evening.
Will allow ramp-down details tbd as the time comes.
A weak cold front will drop across waters Sat. Timing a bit uncertain...and
mixed profiles should be less than ideal. Will opt to cap winds at 15 knots
at this time. Otherwise...no hazardous conds expeceted through the weekend.
abundantly dry air will accompany the Arctic airmass invading the
area on Thursday...with dew points below zero expected. This will
result in relative humidity values bottoming out in the teens
Thursday afternoon. The dry and windy conditions may result in an
enhanced fire spread potential Thursday afternoon depending on how
much rainfall the area receives today. Stay tuned.
tidal departures running around a foot this morning with southerly
winds continuing to increase the anomaly. Levels running close to
latest cbofs model output...which shows conditions near minor
flood criteria near Annapolis and perhaps the North Shore of the
lower tidal Potomac. The anomaly would need to increase to nearly
2 feet for flooding in Baltimore and about 1.7 feet for Solomons
Island. With high tide now just 3-8 hours away...it appears
unlikely those values will be reached. Will keep the coastal Flood
Advisory as is for Calvert/Anne Arundel/Saint Marys only.
Water levels will sharply decrease following frontal passage...and
a negative anomaly over one foot is likely by Thursday afternoon.
District of Columbia...Wind Advisory from 6 PM this evening to 11 am EDT Thursday for
Maryland...Wind Advisory from 6 PM this evening to 11 am EDT Thursday for
Coastal Flood Advisory until 5 PM EDT this afternoon for
Virginia...Wind Advisory from 6 PM this evening to 11 am EDT Thursday for
WV...Wind Advisory from 6 PM this evening to 11 am EDT Thursday for
Marine...Small Craft Advisory from noon today to 6 PM EDT this evening
Gale Warning from 6 PM this evening to 6 PM EDT Thursday for
Small Craft Advisory until 6 PM EDT this evening for anz533-
Gale Warning from 6 PM this evening to 6 am EDT Thursday for