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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
712 PM EST Thursday Jan 29 2015

Synopsis...
a cold front will swing through the region tonight. High pressure
building into the region will bring windy and cold conditions
Friday and Friday night. The high will build over the area
Saturday...but low pressure may impact the area later Sunday into
Monday. Cold high pressure will return for the middle portion of
next week.

&&

Near term /until 6 am Friday morning/...
extended Winter Weather Advisory for portions of western
Maryland...eastern WV Panhandle and far northern Shenandoah Valley of
Virginia for a couple hours as there is still some lingering precipitation
to move through and there still may be some freezing rain or
freezing drizzle associated with it before p-type would likely
change to just snow overnight.

Have kept the advisory in effect further downstream for now as
well. Main band has moved east...but can/T rule out patchy
freezing drizzle or flurries leftover especially near the Mason
Dixon line.

Even those areas where precipitation is done...temperatures already below
freezing or dropping below freezing overnight will result in some
slick spots overnight into early Friday morning.

Previous...

A wintry mix of freezing rain...sleet and snow is expected for much
of the outlook area this afternoon and early evening and therefore a
a Winter Weather Advisory is in effect.

High pressure continues to move off the Carolina coast this
afternoon and southerly flow has increased across the region. A cold
front is draped from Lake Erie to Ohio/in to Kentucky. Ahead of the cold
front and in response to a shortwave trough and warm air advection...precipitation
will continue to move across the Appalachian Mountains and Highlands this
afternoon. A nose of +3 warm air will continue to move into the region at
850mb. Southerly flow at the surface has allowed temperatures to climb but cold
surfaces from recent cold temperatures and snowpack has slowed them from
climbing much. Many observation are at or below freezing around Washington District of Columbia and
Baltimore and north and west are such that. Southerly flow at the
surface has mainly allowed temperatures in valleys in central
foothills...Piedmont and southern Maryland to rise to the middle to upper
30s. This trend will continue as boundary layer winds are expected
to increase to 10-15kts. This is a borderline event since many Road
temperatures are above freezing but mesonet observation are not. Even though ASOS
and AWOS sites are well above freezing...many observation between those
sites are not. Therefore...precipitation moving eastward may melt
and freeze on contact especially on untreated surfaces. Further
north near the Maryland/PA border...colder temperatures aloft may lead to more
sleet and snow than freezing rain but all frozen ptypes are possible today.
Therefore a Winter Weather Advisory was issued for this afternoon
and evening.

The hrrr has been following the precipitation rather well this
morning. Anticipate precipitation to be east of the western shore of
the Chesapeake Bay by 8pm. Temperatures south of Washington District of Columbia are expected
to be above freezing and therefore rain and sleet are the main
precipitation types in this region. The front will follow behind and move across
the middle-Atlantic tonight reaching the Chesapeake Bay by late
tonight. Northwest winds will move in behind the front and upslope snow
showers are expected across the western slopes of the Allegheny
Front. Snow accumulation is expected as lapse rates steepen in the
snow growth zone. A Winter Weather Advisory continues for the
western slopes for accumulating snow into Friday. Accumulation of
4-8 inches are possible in these locations.

Vorticity advection will be rotating around the main trough
tonight and tomorrow. Dry westerly wind east of the allgheny front
should limit precipitation from reaching the ground. Forecast min temperatures will
reach the 20s in the mountains and low to middle 30s from Washington District of Columbia and
south and east along I-95.

&&

Short term /6 am Friday morning through 6 PM Friday/...
high pressure building into the middle Atlantic will lead to a strong pressure gradient
across the area. This in turn will lead to a windy day. BUFKIT
x-sections are showing inxs of 40 knots a few thousand feet off the grnd.
This will have the potential to be brought to the surface. We are advsrtsg the
possiblity of a Wind Advisory - most likely areas will be above 1500 feet and
across the northern 1/2 of the forecast area.

Highs in the lm30s.

&&

Long term /Friday night through Thursday/...
high pressure building over the range Friday night will lead to chilly temperatures. Lows
in the teens across much of the area. Winds will be diminishing
overnight...but west/ cold temperatures winds chills expeceted to be in the single
digits east of the mountains presently seeing values as low as -14 in The
Highlands. If this trend continues a Wind Chill Advisory will be needed
for our far western area.

Sat looks to be M sunny but cold west/ highs ranging from the u20s to
the mu30s over most of the area.

Sat night will be cold...but a little warmer than Friday night. No winds so
wind chill will not be a concern.

What had been a split in the models between a low track to our north
and another track to our south seems to be consolidating around the
southern track now...taking it east through S Virginia or NC. That supports
snow for much if not all of our region. Would be passing through at a
good clip but accumulating snow certainly a possibility for Sun
afternoon into Monday morning.

High pressure will follow for Tuesday. Next cold front poised for
Wednesday.

&&

Aviation /00z Friday through Tuesday/...
a wintry mix is expected this afternoon and evening for the
terminals. Precipitation will move quick and from west to east through the
region today ending across BWI-mtn-dca by 8pm. MVFR conditions
possible at mrb-iad-dca-mtn-BWI as colder air further north gives a
greater potential for snpl. Further south..cho should stay rapl. S
winds 10-15kts will continue today and tonight ahead of a cold
front. A strong frontal passage is expected tonight with northwest winds 20-25kts g
35-40 expected late tonight and Friday across the terminals.

Windy conds Friday and Friday night as high pressure builds into the area. No
probs expeceted aviation-wise Sat or Sat night.

Snow and IFR conditions are possible Sunday afternoon into Monday
morning as low pressure slides by to our south. VFR for Tuesday.

&&

Marine...
a wintry mix will move across the waters this evening. A mix of snow
sleet and rain are possible but should end by late tonight.
Southerly winds will continue on the waters through tonight before a
strong frontal passage moves across the waters by Friday morning. Northwest winds
20-25kt gust around 45kts possible. Small Craft Advisory are in effect and will
transition to a Gale Warning Friday.

A Gale Warning is in effect from Friday morning through the Erly hours of Sat
morning..and then an Small Craft Advisory will likely go into effect aftrwards for the
remainder of the night. Winds will be diminishing for Sat and Sat night.

Gusty winds and a Small Craft Advisory are possible on Monday into
Monday night as low pressure intensifies offshore.

&&

Lwx watches/warnings/advisories...
District of Columbia...Winter Weather Advisory until 9 PM EST this evening for dcz001.
Maryland...Winter Weather Advisory until 9 PM EST this evening for
mdz003>006-011-013-014-502>508.
Winter Weather Advisory until noon EST Friday for mdz501.
Virginia...Winter Weather Advisory until 9 PM EST this evening for vaz028-
031-052>054-501-505-506.
Winter Weather Advisory until noon EST Friday for vaz503.
WV...Winter Weather Advisory until 9 PM EST this evening for
wvz050>053-504.
Winter Weather Advisory until noon EST Friday for wvz501-503-
505.
Marine...Small Craft Advisory until 6 am EST Friday for anz530>534-
537>543.
Gale Warning from 6 am Friday to 1 am EST Saturday for
anz530>543.

&&

$$
Bpp/has/Woody!/Cas

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