Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Baltimore Maryland/Washington District of Columbia
414 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/...
low pressure early this morning has been strengthening as it moved
through the western Ohio Valley...with a nearly stationary front
extending east of it to near the Mason Dixon line. High pressure has
wedged in east of the Appalachians...and with little cloud cover
most of the night temperatures have dropped into the upper 30s and
40s over most of the forecast area. Radiational cooling is expected
to diminish over the area early this morning as high clouds have
moved in ahead of the low pressure to our west.
Northern and southern stream energy will merge today while upper
trough digs through the Ohio Valley. This will support
strengthening of the surface low as it moves towards the East Coast
along the frontal boundary. Although there are still some model
differences in exact strength and track of the low...it should at
least skirt the northern portion of the forecast area during the day
today before moving into New Jersey by this evening.
This track supports at least most of the forecast area being in the
warm sector today. Short-term models indicate potential of
pre-frontal showers...followed by a line of convection developing
along the front. Winds aloft will be strong throughout the vertical
column...with the 850 jet increasing to around 40-50kt as it crosses
the area. So wind shear will be favorable for severe
convection...but main question will be the amount of available
instability due to antecedent cloud cover and potential of showers
ahead of the main line of convection. Region remains in a slight
risk of severe thunderstorms per Storm Prediction Center today. Main threat would be
damaging straight line wind gusts...along with an additional tornado
threat given strong speed and directional shear.
High temperatures today forecast to reach the upper 60s to low 70s
east of the Blue Ridge...although temperatures could be curtailed by cloud
cover and a cool start to the day. Generally 60s over WV and northern
Maryland...and cooler at the ridge tops.
Short term /6 PM this evening through 6 PM Thursday/...
behind the cold front...very strong pressure gradient will build
around the back side of the low. This will have two impacts. The
first will be very gusty synoptic scale winds. Have issued a Wind
Advisory for most of the forecast area this evening and into
Thursday morning for potential wind gusts up to 50mph. The second
will be a rapid drop in temperatures as the low pulls down very cold
and dry air. Singe digit lows expected over the Potomac
Highlands...the teens for other locales along and west of the Blue
Ridge...and the 20s to the east. Combined with gusty winds...single
digit wind chills are likely in most locations...with sub zero wind
chills over the mountains and possibly colder than 0-10 at the
Potomac Highlands. Day shift will need to consider headlines for
wind chills tonight.
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 /08z Wednesday through Sunday/...
VFR conditions to start Wednesday. 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 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 increase today...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 0f 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 Wednesday into Wednesday evening.
tidal departures running about a half-foot above normal Ely this morning. Southerly
winds will be incrsg today...providing a good push to enhance the
incoming tide...especially the afternoon-evening cycle. Latest indications
suggest that the tide should make it to the northern reaches early
this evening before a wind shift to the west/northwest occurs. /High tide
Annapolis approx 345 PM...balt 415-530 PM...and Havre Delaware Grace 8pm./
Results of model guidance mixed...but cbofs hits minor threshold at
Baltimore and comes close at Annapolis. We only need an additional
foot of water at St George Island...Solomons Island...Annapolis for
minor inundation to occur. In this pattern...think thats doable.
Balt need 1.5 feet. Thats possible but not so certain-- cbofs seems to
be verifying OK so far. On the other hand...hdg needs 2 feet which is
looking more doubtful. Hec-Ras is suggesting that the upper ptmc will be
OK...but its bias is to not recognize a surge coming upstream.
Considering some of the uncertainties...went with an advsy only for
locations where the additional water needed for minor flooding to
occur is 1 foot...which also happens to be where the high tide comes
sooner. Will brief day shift...who can update as needed.
Once the Wednesday night tide pulls out...water should be driven out...and will
be talking about negative water level departures by Thursday.
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 from 11 am this morning to 5 PM EDT
this afternoon for mdz014-017-018.
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 from 8 am this morning to 6 PM EDT this
evening for anz533-534-537-541-543.
Gale Warning from 6 PM this evening to 6 am EDT Thursday for