Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 190133

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
933 PM EDT Fri Aug 18 2017

A cold front will cross the region tonight. Surface high
pressure will build in Saturday, but an upper level disturbance
will cross the region Saturday night. A warm front will advance
back north across the region early next week, followed by a
strong cold front in the middle of the week.


Heat Advisory, Severe Thunderstorm Watch, and Flash Flood Watch
have all been cancelled. The line of thunderstorms that
developed along a prefrontal trough and ahead of a shortwave
trough aloft is now moving into southeast Virginia and the
Eastern Shore.

The surface cold front is now moving into western Maryland and
the eastern West Virginia panhandle. Ahead of it, some elevated
instability remains, so have left a slight chance of showers in
the forecast for several more hours. A couple of showers
recently formed near Hagerstown.

The front will slowly push through the area tonight, but
moisture will be slow to dwindle until it does. Have left
patchy fog in the forecast, though have low confidence in its
occurrence, particularly since mid level clouds seem to be
forming in the frontal zone. Lows will be a bit cooler than last
night, with 60s and low 70s expected.


Other than patchy fog, Saturday should start out tranquil with
some sun. Humidity will be lower, though temperatures will only
be a few degrees less than today. However, potent upper level
trough will move into the region late in the day and at night,
and it appears enough moisture will remain to result in isolated
showers and t-storms late in the day into the evening.

High pressure dominates Sunday for the most part, with
temperatures expected to drop a bit further once again - the
most comfortable day of the weekend. However, warm front will
start poking back north late in the day and at night, and that
may result in a return risk of showers in central VA.


High pressure will move offshore Monday and settle into
Tuesday, allowing for southerly flow to settle over our area.
Moisture advection could enhance diurnally driven showers and
thunderstorms Monday and Tuesday afternoon/evening. An upper
trough and strong cold front will approach from the northwest on
Tuesday night into Wednesday, bringing additional chance of
showers and thunderstorms on Wednesday. The front should move
across on Wednesday night with a high pressure returning
Thursday into Friday.

High temperatures Monday through Wednesday will be in the mid
to upper 80s in Northern Maryland... to low 90s in Central
Virginia at times... and 70s at higher elevations... highs in
the 70s and 80s Thursday and Friday.


The threat for thunderstorms has ended, though can`t totally
rule out a rogue shower until frontal passage. The front is in
western Maryland this evening and will progress east overnight.
Have limited BR mention to CHO, where front will take longest to
clear...although overall confidence in any fog is low.

Otherwise, expecting VFR Saturday, though an isolated shower or
t-storm is possible late. Mainly VFR again Sunday with high
pressure dominant.

VFR conditions expected Monday into Wednesday, with periods of
sub-VFR conditions mainly Monday and Tuesday afternoon/evening
and Wednesday due to possible showers and thunderstorms.


Line of storms will continue to move east of the middle Bay
through late evening, ending the threat for Special Marine
Warnings. There is a lull in winds behind the storms, but
northerly channeling will be possible overnight as the actual
cold front passes, so SCA continues for main channel until early
morning. For balance of Saturday, should be sub SCA, but an
isolated gusty t-storm is possible late in the day as an upper
trough moves on through. Returning to tranquil conditions

Mainly dry conditions expected Monday into Wednesday, with
periods of showers and thunderstorms possibly developing Monday
and Tuesday afternoon/evening and Wednesday. Wind gusts are
expected to stay below the small craft advisory threshold.


Southerly flow will continue to cause elevated water levels
through tonight. CFA for St. Mary`s through tonight. Most
concern for an additional advisory is at Annapolis, but want to
see how water recovers after sloshing from thunderstorms. Will
keep an eye on DC and Baltimore as well. Cold front crossing
late tonight will bring NW/N winds and decreasing water levels.


MD...Coastal Flood Advisory until 3 AM EDT Saturday for MDZ017.
MARINE...Small Craft Advisory until 9 AM EDT Saturday for ANZ531>534-
     Small Craft Advisory until 1 AM EDT Saturday for ANZ530-535-


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