Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 181853

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
253 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.


Low clouds have given way to sunshine and a south to southwest
flow has ushered in hot and humid conditions. Max temps will
range from the upper 80s to lower 90s for most locations. The
hottest conditions are expected along the Interstate 95 urban
corridor...with heat and humidity causing heat indices around
100 degrees. Did cancel the heat advisory for Washington DC
since max temps will be a couple degrees cooler. This should
keep heat indices around 100 degrees instead of 105 degrees.

The heat and humidity has led to an unstable atmosphere this
afternoon. Latest mesoanalysis shows 1500-2500 J/KG of MLCAPE.
Shear profiles remain relatively weak and there is no strong
lifting mechanism to initiate convection.
Therefore...thunderstorm coverage is expected to remain
isolated to widely scattered through early this evening.

Any convection should dissipate after sunset.
However...additional showers and thunderstorms may propagate
into western portions of the CWA overnight ahead of an
approaching cold front. Confidence is low due to the unfavorable
timing...but with the warm and humid conditions overnight there
will be some instability. Also...shear profiles will be
strengthening as a cold front and its associated upper-level
trough approach from the west. A few severe thunderstorms cannot
be ruled out overnight...mainly toward the Allegheny and Potomac


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 to widely scattered thunderstorms are expected through
early this evening. A line of thunderstorms well to our west may
propagate toward the terminals late tonight into Monday
morning...but it should weaken as it does so and confidence is
low that it even makes it at all. Did allow for a VCTS during
this time.

There is a better chance for showers and thunderstorms later
Monday 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.
Isolated thunderstorms are expected late this afternoon and
evening. Thunderstorms may produce locally gusty winds but most
places will end up dry due to the limited coverage.

There is a better chance for thunderstorms later Monday through
Monday evening. Some of these storms may become severe with
damaging wind gusts being the primary threat. A Small Craft
Advisory is in effect for portions of the waters Monday night.
A Small Craft Advisory may be needed for portions of the waters
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 from 11 PM this evening to 4 AM EDT
     Monday for MDZ014.
     Coastal Flood Advisory from 7 PM this evening to midnight EDT
     tonight for MDZ017.
VA...Heat Advisory until 6 PM EDT this evening for VAZ054.
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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