Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 190030

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
830 PM EDT Sun Jun 18 2017

A very warm and humid air mass will remain in place
through Monday until a cold front clears the area Monday night.
Weak high pressure will build over the area for the middle of
the week.


SPC Mesoanalysis this evening depicting plenty of instability
with MLCAPE values ranging from 1000-2000 J/KG; however thin
stable layer around 850mb combined with lack of a true trigger
has led to only isolated to perhaps scattered convective
activity this evening. This activity has been mainly focused
west of the Blue Ridge where terrain has helped to serve as an
focus for initiation, and slightly lowering heights has
provided for a bit better environment for cell development. That
being said, main shear axis remains well to the west this
evening, and any activity that can/does develop will be pulse in

Overnight main area of convection over the Ohio Valley will try
to push eastward, however this should be decaying by the time it
reaches the Allegheny Front later tonight. Thus severe threat
should be lessening.

Otherwise, warm and muggy night in store with lows in the 70s
pretty much area-wide.


A cold front will approach the area from the west Monday before
passing through Monday night. Showers and thunderstorms are
expected along and ahead of the cold front. A southwest flow
ahead of the boundary will usher in more unstable conditions and
deep layer shear will increase as the upper-level trough
associated with the boundary shifts toward our area. The
combination of stronger shear profiles...lift associated with
the cold front and unstable conditions suggests that severe
thunderstorms are possible. The main threat appears to be
damaging wind gusts due to the unidirectional flow with height.
Still...confidence is low because there are some limiting
factors. One is that mid-level clouds may cut back on
instability some and the other is that convection overnight has
the potential to outrun the cold front and move into our area.
If this will be tougher for the atmosphere to
recharge from daytime heating especially across western areas
of the CWA.

As of now...the better chance for stronger to severe
thunderstorms is east of the Blue Ridge Mountains Monday
afternoon through Monday evening. Plenty of moisture will be in
place so thunderstorms will have the capability of producing
torrential downpours. Contemplated a Flash Flood Watch...but the
uncertainty as to exactly where the heaviest storms will
develop is still high. There is a chance that the torrential
rains could develop farther east where Flash Flood Guidance is
higher. Will re- evaluate tonight into Monday morning.

Convection will dissipate overnight behind the cold front. Weak
high pressure will build overhead for Tuesday and Tuesday night.
Less humid conditions along with seasonably warmer temperatures
are expected.


Mostly dry conditions for most of our CWA early on Wednesday
with some showers possible in the SE region due to a nearby
front. Some afternoon convection possible Wednesday afternoon
into the night due to departing trough, but mainly dry
conditions expected. Dry conditions continue into Thursday and
early Friday as zonal flow and a drier air mass settles in. On
Friday and into the weekend uncertainty increases as guidance
diverge on solutions. Tropical moisture and approaching
boundaries will allow for what it looks like a period of showers
and thunderstorms Friday and into Sunday.


Isolated showers/thunderstorms are expected through this
evening, but very low likelihood of impact to any TAF site. A
complex of thunderstorms well to the west may propagate towards
the terminals late tonight into Monday morning...but it should
weaken as it does so, with only showers and isolated thunder
when it does move eastward.

There is a better chance for showers and thunderstorms after
noon Monday and into Monday night. Some storms may be severe
and the best chance for severe storms will be across the eastern
terminals. Weak high pressure will build toward the terminals
late Monday night through Tuesday night.

Dry/VFR conditions expected Wednesday into early Friday. Some
scattered showers and thunderstorms Wednesday and Friday
afternoon which could cause periods of sub-VFR conditions.


South to southwest flow will continue through Monday. A Small
Craft Advisory is in effect for the waters during this time.

As a cold front pushes into the region, showers and
thunderstorms become likely Monday through Monday evening. Some
of these storms may become severe with damaging wind gusts
being the primary threat.

A Small Craft Advisory continues for portions of the waters
Monday night and it may need to be extended for Tuesday into
Tuesday night.

Dry conditions expected Wednesday into early Friday.
Some scattered showers and thunderstorms Wednesday and Friday
afternoon. Winds will be below the small craft advisory criteria
through early Friday, when wind gusts could reach 18 kt.


A southerly flow will cause tidal anomalies to increase through
tonight. A Coastal Flood Advisory is in effect for sensitive
areas of Anne Arundel County...Washington DC and St Marys
County for the high tide cycle tonight.

Elevated water levels are expected through Monday night due to
the southerly flow. Additional minor flooding is possible near
times of high tide.


DC...Coastal Flood Advisory from 2 AM to 6 AM EDT Monday for DCZ001.
MD...Coastal Flood Advisory until 4 AM EDT Monday for MDZ014.
     Coastal Flood Advisory until midnight EDT tonight for MDZ017.
MARINE...Small Craft Advisory until 9 PM EDT Monday for ANZ530-531-535-
     Small Craft Advisory until 6 AM EDT Tuesday for ANZ532>534-537-


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