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Area forecast discussion...updated 
National Weather Service Baltimore Maryland/Washington District of Columbia
920 PM EST sun Feb 7 2016

Synopsis...
low pressure will pass well to our south and east overnight.
Another low pressure system will dive south into the Ohio Valley
Monday before passing through our area Monday night into Tuesday.
High pressure will slowly build toward our area during the middle
portion of next week.

&&

Near term /through Monday/...
high clouds associated with storm system off the NC coast should
thin out overnight leading to clear skies by daybreak.

Height falls associated with ampliflying upper level trough over
the Great Lakes will induce surface low development over southern Virginia Monday
night. Precipitation will develop east of upper trough axis Monday and spread
quickly across the entire area Monday afternoon. Guidance is still
in disagreement with respect to onset/timing of precipitation with 18z
GFS/gefs faster than 12z European model (ecmwf). Given that there is a chance that
precipitation could start before 18z Monday decided to issue a Winter Weather
Advisory for the five western most counties. This was all
coordinated/collaborated with rlx and pbz.

&&

Short term /Monday night through Wednesday/...

Update...precipitation type issues and potential for dry slot to work northward
into our southern counties make for uncertain forecast details but
confidence is high that evening rush hour commute Monday will be fine
as surface temperatures are expected to be above freezing. Since any impacts
are not likely to occur until Monday night...we'll not issue any
advisories any further east.

Previous discussion...

As the sunsets Monday night and low pressure forms off the middle-
Atlantic coast rain will transition to snow overnight and into Tuesday
morning. Thermal profiles across the region with the exception of
higher elevations will limit snowfall accumulation when snow
begins Monday night into Tuesday morning. As temperatures begin to rise
Tuesday in the low lands and east of the Blue Ridge snowfall will
be difficult to accumulate unless banding occurs across the
region. As stated many times with this system...moisture and quantitative precipitation forecast
fields differ in model guidance as most of the banding activity
will be convective in nature. The strong 925- 850mb easterly jet
once the surface low forms along the coast will allow instability to
increase and snowfall rates to increase. At this time location and
exact timing of these instability bands are uncertain but the
best timing will be Tuesday morning into Tuesday evening.

The snowfall accumulation forecast is thermally based with snowfall
totals higher where boundary layer conditions are colder for snow
such as near the Maryland/PA border...higher elevations and the western
slopes of the Allegheny Front. Further south and east...temperatures will
reach the middle to upper 30s Tuesday and snowfall will likely
accumulate and melt and drier air will likely move into central Virginia
Tuesday. Accumulations of 3-6 inches expected across the northern half
of the middle-Atlantic and 1-3 in the southern half with higher amts
along the ridges.

The broad upper level trough will stay across the area into
Wednesday and scattered snow showers will be possible. Light
accumulation is possible across the region. Snow showers are
expected across the western slopes of the Allegheny Front as northwest
winds continue to draw down moisture from the Great Lakes.
Accumulating snowfall is expected through Thursday for this area
with total snowfall accumulation of 6-8 inches.

&&

Long term /Wednesday night through Sunday/...
the main upper level trough of low pressure will pivot across the
region later in the day Wednesday into Wednesday night. Additional
upslope snow expected in the Potomac Highlands...while an occasional
snow shower or two cannot be ruled out across the I-81 and I-95
corridors. Much colder air will be on the heels of this upper trough
Wednesday night as a cold dome of high pressure builds in from the
west.

High pressure will dominate Thursday and Thursday night with very
cold and dry air across the region. Temperatures will be 10 to 15
degrees below normal.

As the high flattens out late Thursday night into Friday...an area
of low pressure should scoot across the Tennessee Valley. This low
should just spread additional cloud cover across the southern half
of our region. A brief period of light snow cannot be ruled out
across the Virginia Piedmont to the mouth of the Chesapeake Bay.
Very cold temperatures will continue Friday into Friday night with
temperatures about 10 to 15 degrees below normal.

Behind the area of low pressure...the main upper level trough of
support will pivot east with a firm ridge of high pressure quickly
to follow it. Aside from diurnal cloud cover Saturday...this trough
will mainly support Arctic air surging into the middle Atlantic
Saturday and Saturday night.

The same ridge of high pressure building into the region will become
reenforced Sunday into Sunday night. Thus...high and low
temperatures will remain well below normal with the potential of
experiencing lows in the single digits below zero to highs in the
teens across a large portion of the region.

&&

Aviation /02z Monday through Friday/...
ceilings expected to drop quickly Monday afternoon with a rain/snow mix most
taf sites except all snow at kmrb.

Timing of changeover to snow and precipitation rates Monday night remain in
question at this time.

-Snsh possible Wednesday as upper level trough continues to move
overhead. Prevailing VFR conditions expected Wednesday.

MVFR conditions Wednesday with a chance of snow showers at any
terminals. Winds west to west-northwest 5 to 10 knots gusts 15 knots
Wednesday. VFR conditions Wednesday night. Winds west-northwest 5
to 10 knots gusts 15 knots.

&&

Marine...Small Craft Advisory conditions currently being observed
over the Lower Bay and Potomac but model trend is for winds to
strengthen through 06z Monday then diminish as deep coastal low moves
further away.

Northwest winds will increase Tuesday afternoon and continue
through the end of the week. Small Craft Advisory conditions
likely Tuesday through much of next week.

&&

Coastal flooding...water levels are up to half a foot above normal on
the waters this evening. North flow becomes southeasterly Monday afternoon with
water levels increasing through Monday night as low pressure crosses the
area. Minor coastal flooding at sensitive sites is likely around
high tide Monday night into Tuesday.

&&

Lwx watches/warnings/advisories...
District of Columbia...none.
Maryland...Winter Weather Advisory from noon Monday to 1 am EST Tuesday
for mdz501-502.
Virginia...Winter Weather Advisory from noon Monday to 1 am EST Tuesday
for vaz503-504.
WV...Winter Weather Advisory from noon Monday to 1 am EST Tuesday
for wvz501>506.
Marine...Small Craft Advisory until 9 am EST Monday for anz532>534-537-
540-541-543.

&&

$$
Synopsis...lfr
near term...lfr
short term...has/lfr
long term...klw
aviation...lfr/klw
marine...lfr/klw

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