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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
949 am EST Thursday Dec 18 2014

Synopsis...
high pressure will build into the area today and persist through
Friday night...except for a weak disturbance that will cross the
area tonight. Low pressure will track south of the area Saturday
through Sunday. A secondary low is expected to move up from the
southeast coast early next week. A large area of low pressure
looks to develop in the Ohio Valley during the middle of next
week.

&&

Near term /through tonight/...
surface high pressure centered near Lake Superior will extend southeast
toward the area today...while still under the influence with the
pressure gradient to low pressure over the Canadian Maritimes.
Stratocumulus extends across the northern third of the County Warning Area and has
actually advance a bit back to the southeast over the past few hours.
Still think this layer can at least become more scattered with
diurnal mixing...but may be a slow process. Another shortwave
trough is quickly approaching from the lower Ohio Valley. Hi res
models continue to show precipitation fizzling as it encounters drier air
mass/high pressure...and the last couple hours of radar data
support the hypothesis. There is a better latching onto the
northern area surviving across Ohio...so will monitor radar trends
as to whether probability of precipitation may needed to be added late afternoon/evening
in the northern mountains. Otherwise just an increase in middle level
clouds expected. Expect the sporadic wind gusts to become more
common toward midday as the 20-25 knots seen on the 12z kiad sounding
are able to mix down. Sounding also supports going high
temperatures combined with a bit of downsloping...so no adjustments
there.

Will have some clouds from the system in the centrl of the Continental U.S. Advcg eastward
by end of the period. Will be mostly cloudy as a result in the evening as WV crosses
County warning forecast area. NAM suggesting schc probability of precipitation...maybe due to a flurry or two. Air mass
looks too dry for that. Went lower than NAM probability of precipitation...precluding a
mention...but pop grids nonzero. Took temperatures down by a cpl degf in
cold air advection.

&&

Short term /Friday through Friday night/...
overall synoptic pttn Friday simlr to today...minus the S/wvs. Have fewer
clouds in the grids...and simlr temperatures. Aftr midngt...will have middle deck
clouds filling in from the SW...but forecast pace of storm system has
slowed...which impacts skycover. NE of ptmc river skycover may average
out no worse than partly cloudy.

&&

Long term /Saturday through Wednesday/...
high pressure will be centered over Quebec and extend down into the
middle-Atlantic Saturday. A shortwave trough will be approaching the
Ohio Valley and southerly flow aloft will cause moisture
advection into the region Saturday causing clouds to build in from
the southwest. A jet streak will be located across the southeast states
with most of the forcing across this region including the
Carolinas Saturday into Saturday night. Flow at 850 veers westerly
across the middle-Atlantic Sat afternoon and shuts off moisture
advection from the Gulf. This will result in lighter precipitation across
the region. Most of the moisture will be further south and across
the Carolinas. The 3z sref mean has lined up more with the
deterministic runs showing mostly dry conditions Saturday into
Sunday. Temperatures are expected to climb into the 40s Saturday and any
precipitation will be rain with the exception of the higher elevations
that would see snow. Light precipitation is expected and therefore little
to no accumulation of snow in the mountains is expected at this time.

The shortwave trough will move off the East Coast by Sunday and
ridging will allow drier air to filter in from the west. A brief
period of calm weather is expected Sunday before the next system
begins to form off the southeast coast Sunday night. A trough will move
into the Gulf Coast states and cyclogenesis is expected to take
place off the southeast coast Monday into Tuesday. Temperatures are
forecast to be above freezing with the exception of the higher
elevations Monday night. Mostly rain is expected during this time.
Low pressure should move away from the middle-Atlantic Tuesday. Little
relief is expected as the next strong system moves into the Great
Lakes region midweek. Timing is everything and moisture with this
systems seems to be pre-front and therefore the mid=atlantic would
see mostly rain.

&&

Aviation /15z Thursday through Monday/...
VFR conditions today with broken ceilings at times 040-050 (except cho)
and wind gusts to 20kt possible. Ceilings will scatter out by this
afternoon. The gusty northwest winds will become more consistent through
this afternoon...then diminish by evening.

Will have a period of middle deck clouds this evening. Think winds will subside at the
surface...but will still have 20-25 knots flow 1000 feet up. Not enough to qualify
for low level wind shear.

VFR continues Friday-Friday night. Anthr period of gusty northwest winds midday up to 20
knots. Once again...middle deck clouds will overspread terminals at night.

No significant weather expected Saturday and Sunday.

&&

Marine...
Small Craft Advisory caliber gusts will continue through the afternoon. Morning
analysis suggests northwest gusts 20-25 knots with mixing. These winds will
diminish through the afternoon...no changes to the Small Craft Advisory dropping
off at 19z for the upper Potomac and 00z elsewhere.

Guidance suggesting that flow will partially dcpl tonight. Am not certain
of that...but will cap winds just below for the night time period. The
opportunity for mixing renews after sunrise Friday. Have issued anthr
Small Craft Advisory for most of the Bay and lower ptmc river through middle afternoon.

A disturbance will move south of the waters Saturday and Sunday. An
active period is expected next week. Coastal low pressure may impact
the waters Monday.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...none.
Virginia...none.
WV...none.
Marine...Small Craft Advisory until 7 PM EST this evening for
anz530>534-537>543.
Small Craft Advisory from 7 am to 3 PM EST Friday for
anz531>534-537>543.
Small Craft Advisory until 3 PM EST this afternoon for anz535-
536.

&&

$$
Synopsis...heights
near term...ads/hts
short term...heights
long term...has
aviation...ads/has/hts
marine...ads/has/hts

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