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Area forecast discussion 
National Weather Service Baltimore Maryland/Washington District of Columbia
319 am EDT Tuesday Oct 13 2015

a cold front will pass through the region today. High pressure
will build overhead tonight through Thursday. Another cold front
will pass through the area Friday and Canadian high pressure will
build overhead during the weekend.


Near term /through tonight/...
a cold front is moving through the Ohio Valley early this morning
and a southerly flow ahead of the boundary has allowed for
noticeably milder conditions compared to recent mornings.
However...a line of showers ahead of the front is expected to move
through our area from west to east this morning. Most of the middle
and upper-level support with the cold front will remain off to our precipitation amounts will be light. The best chance
for showers will be between 5 and 8 am for locations west of the
Blue Ridge mountains...and between 8 am and 11 am for the
Washington and Baltimore metropolitan areas.

The actual cold front will pass through the region from west to
east this afternoon...but most areas will remain dry during this
time due to subsidence behind departing shortwave energy.
Also...with some sunshine expected and a downsloping westerly flow
behind the cold front it will turn out to be another warm
afternoon. Maximum temperatures are forecast to range from the 50s along the
Allegheny Front to the middle and upper 70s near Washington and
Baltimore. The forecast leans toward the warmer side of guidance
due to the downsloping flow and sunshine expected this afternoon.

The cold front will move off to the east tonight while high
pressure builds into the Midwest. A west to northwest flow will
usher in cooler conditions during this time. Min temperatures will range
from the upper 30s along the ridge tops of the Allegheny Highlands
to the middle 50s in Washington and Baltimore.


Short term /Wednesday through Thursday night/...
high pressure will build into the Ohio Valley Wednesday before
settling overhead Thursday into Thursday night. Dry and cool
conditions are expected during this time along with sunshine. It
will be breezy Wednesday with winds gusting around 20 to 25 miles per hour
and there may be scattered/broken cumulus deck as a weak upper-level trough
remains overhead.


Long term /Friday through Monday/...
00z model showing slightly quicker progression of the cold front
Friday...with it now offshore by 00z Sat. Continues to be mainly a
dry passage for most of the County Warning Area. Have slight chance probability of precipitation for
northwestern areas and along the Mason- Dixon...closer to the
upper level support as well as possible terrain influences. Any precipitation
that does form will quickly end by Friday night...with broad high
pressure building in for the weekend.

Dry weather for the weekend...with well below normal temperatures...and
frost/freeze potential becoming the big story. Strong surge of cold air advection over
the area as the high builds in...with the northern stream trough
dipping well south of the area. While there still remains some
differences in the temperatures...with the GFS on the cooler side than the
European model (ecmwf)...the agreement is there of seeing 850mb temperatures dropping below
0 degrees celsius. Lows Friday night still predominately in the
40s...with spots out west hitting the middle 30s. With light winds and
clear skies...strong radiational cooling should lead to most of the
area seeing sub-40 Sat and sun nights...with a good portion of the
Potomac Highlands dipping to near or below freezing. Will have to
continue to monitor with the potential for frost/freeze products.
Highs Sat and sun will hover in the 50s.

Ridging building in from the west late in the weekend will nudge the
trough on east...allowing for a warm up to start the week. High
pressure dominating the region keeps things dry and quiet.


Aviation /07z Tuesday through Saturday/...
VFR conditions are expected most of the time through Thursday
night. A line of showers will impact the terminals this
morning...and a brief period of MVFR visibilities cannot be ruled out.
West to southwest winds will gust around 20 knots this afternoon.

West to northwest winds are expected behind a cold front tonight
through Thursday night. Gusts up to 20 knots are possible
Wednesday afternoon and again Thursday afternoon.

VFR conditions for the end of the week through the weekend.


a southwest flow has increased ahead of an approaching cold front
this morning. A Small Craft Advisory is in effect for the Maryland
Chesapeake Bay south of Pooles Island and lower tidal Potomac
River this morning. The Small Craft Advisory is in effect for all
of the waters this afternoon and evening as the mixing layer
increases. A cold front will pass through the waters later this
afternoon into this evening. West to northwest winds are expected
behind the boundary tonight through Thursday. A Small Craft
Advisory is in effect for portions of the waters tonight and
Wednesday. A Small Craft Advisory may be also be needed for
Wednesday night and Thursday.

Small Craft Advisory gusts becoming more likely for Friday with incrsg southerly flow
ahead of the cold front. A brief lull is expected as the front
passes Friday evening. Strong cold air advection will keep gusty northwest winds over the
water...with Small Craft Advisory conditions lasting through the weekend for portions of
the waters.


Tides/coastal flooding...
a southerly flow has increased a bit over the waters. Anomalies
are around one half to three quarters of a foot above normal early
this morning. The anomalies may increase a bit today due to the
southerly flow...but water levels are expected to remain below
minor flooding thresholds. Since the flow will be slightly west of
south...this should prevent anomalies from increasing too much.
Latest guidance along with the forecasted levels remain below
minor flooding thresholds...but it will be close for sensitive
areas such as Annapolis and Washington District of Columbia this afternoon/evening.

An offshore flow will develop behind a cold front tonight and
anomalies will quickly drop.


Lwx watches/warnings/advisories...
District of Columbia...none.
Marine...Small Craft Advisory until 6 am EDT Wednesday for anz531>534-
Small Craft Advisory from noon to 6 PM EDT Wednesday for
Small Craft Advisory from noon today to 6 am EDT Wednesday for
Small Craft Advisory from noon today to 10 PM EDT this evening
for anz530-535-536.


near term...bjl
short term...bjl
long term...bjl/Sears
tides/coastal flooding...bjl

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