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Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
317 PM EDT Sat Oct 1 2016

Low pressure over the Ohio Valley will slowly lift toward the
lower Great Lakes through Sunday. A weak cold front will cross
the area Sunday night, bringing drier conditions for Monday. For
mid to late week, high pressure centered over New England will
extend south over the Mid Atlantic. Tropical cyclone Matthew could
be a factor in our weather by the end of the week.


Expect generally stagnant weather into this evening. Low pressure
is located over the Ohio Valley, beneath the closed upper low that
has been spinning there the past few days. High pressure is wedged
east of the Appalachians. Overrunning in a theta-e ridge is
allowing showers to continue to develop over the eastern part of
the area, with drizzle occurring outside of showers. Elevated
instability exists, so a few rumbles of thunder will remain
possible in the stronger cells. These cells could also produce
heavy rain rates for a time. Meanwhile drier air and breaks in the
clouds are working into the southwest CWA. Expect very minimal
northeast progress with the CAD wedge.

Showers should begin to lift northeast this evening as the dry
slot from the upper low expands east. However, low clouds likely
stick around. It's possible drizzle persists through the night,
especially for north/eastern areas. In the low clouds, a misty fog
is also likely, and if enough clearing works into the southwest,
radiation fog will be possible. The largest diurnal range will be
in the SW, where upper 40s/lower 50s will occur.


RH forecasts show low clouds lifting by midday Sunday, although
have left more clouds than sun in the forecast. Given light low
level flow, would expect weather to side on cooler side of
guidance. As the low pressure center lifts toward the eastern
Great Lakes, a cold front/trough axis will slowly work across the
area Sunday afternoon-night. Given limited moisture and forcing,
only isolated showers are expected, although expanded POPs a bit
over previous forecast.

Northwest flow behind the front will bring a drying trend for good
by Monday. Skies should become partly to mostly sunny. Highs will
be in the 70s with 50s at night.


Nose of strong high pressure...expected to be centered over Maine on
Tuesday...will extend southwestward into the mid-Atlantic and remain
the dominate influence on Mid-Atlantic weather through the mid to
late week. As such, expect cloudy/cool/drizzly conditions as
persistent east/northeast onshore flow develops and strengthens
Tuesday afternoon through the end of the week...resulting in a
classic/hybrid cold air damming scenario...much like we have today.
Model guidance is notorious for over-forecasting high temperatures
and being too optimistic with cloud cover in these scenarios. Thus,
we began the process of nudging high temperatures down and cloud
cover up. 

Tropical Cyclone Matthew perhaps near the Atlantic coast late next
week and over next weekend...but equally at this point could stay
far east and well offshore. At these extended time scales location
uncertainty is extremely high. Never the less, something to watch
over the days ahead.


Expect a fairly persistent forecast through tonight. DCA could try
to sneak into MVFR, and breaks in clouds are not too far south of
CHO. However, looking like IFR, with possible periods of LIFR
through tonight. Showers will be focused near DCA-BWI through
early evening. Can't rule out a rumble of thunder with elevated
instability. DZ possible otherwise.

Guidance indicates improving conditions by midday Sunday, but have
low confidence in this solution due to persistent cold air
damming. There will be a weak cold front Sunday night, which may
help scour out any lingering low clouds. Can't rule out some
patchy fog Sunday night, especially in the south. VFR likely

Sub-VFR conditions...due to low ceilings...could begin to develop
as early as Tuesday afternoon, as CAD scenario becomes established
in the persistent/strengthening onshore flow. Potential for flight
restrictions remains through much of the remainder of the week.


E/NE flow has been gradually weakening this afternoon, allowing
for cancellation of northern portions of the SCA. Still a few
15-20 kt gusts to the south, so will leave SCA in effect. Lighter
and more variable flow should persist through Sunday, as a weak
cold front approaches Sunday night. Winds become NW/N on Monday.

Strengthening onshore flow develops Tuesday afternoon as pressure
gradient tightens...with a small craft advisory looking possible.
Wind possible remain near SCA levels through much of the
remainder of the week as CAD remains entrenched.


Tidal anomalies are still fluctuating between 1.5 and 2 feet above
normal. Coastal Flood Warning for St. Marys this afternoon should
be last iteration of moderate flooding. Minor flooding expected at
other locations (except Havre de Grace) through tonight, although
uncertain whether Baltimore will repeat early Sunday morning.
Annapolis may approach moderate this evening, so interested
parties should remain alert even though only an advisory is in
effect at the moment.Guidance still indicates water levels
dropping tonight, but it may not have a good handle of onshore
flow. Adjustments to headlines will be likely through Sunday as
forecast confidence increases. Monday looks more promising for
water levels to drop with northwest winds.


DC...Coastal Flood Advisory until noon EDT Sunday for DCZ001.
MD...Coastal Flood Advisory until 8 AM EDT Sunday for MDZ016-018.
     Coastal Flood Advisory until 2 AM EDT Sunday for MDZ011.
     Coastal Flood Advisory until noon EDT Sunday for MDZ014.
     Coastal Flood Warning until 8 PM EDT this evening for MDZ017.
     Coastal Flood Advisory from 8 PM this evening to 8 PM EDT 
     Sunday for MDZ017.
VA...Coastal Flood Advisory until 8 AM EDT Sunday for VAZ057.
     Coastal Flood Advisory until noon EDT Sunday for VAZ054.
MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ533-



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