Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 201425 AAA

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
1025 AM EDT Sun May 20 2018

A warm front will lift to our north this morning and a cold
front over the Ohio Valley will drop southeast into our area
tonight. The boundary will stall out overhead for Monday before
another cold front passes through on Wednesday. Weak high
pressure may build overhead for late in the week.



Deep moisture has been shunted to the east as seen on Blended
TPW and differential water vapor RGBs. With continued mid-level
drying today convection will be isolated at best. Will be
trimming coverage to isold for this afternoon. Warmer with temps
climbing into the 80s. Best moisture convergence and thus best
chance of showers will be over southern MD.

Previous afd...

A weak cold front will drop south into the area tonight. A few
showers and thunderstorms are possible ahead of the boundary,
especially across central Virginia into southern Maryland.
Again, coverage should be isolated to widely scattered.


The cold front will stall out over central Virginia by midday Monday
and high pressure will build over the Atlantic during this time.
This will cause the boundary to slowly return north and east as
a warm front, and moisture will increase once again due to a
southwest flow through all levels of the atmosphere. Therefore,
popup showers and thunderstorms are more likely along and behind
the boundary where instability will be highest. Latest guidance
shows the highest likelihood for convection to be across the
Potomac Highlands into central Virginia Monday afternoon.
Convection may spread farther north and east toward the
Washington and Baltimore Metropolitan areas Monday night as the
boundary slowly retreats as a warm front. Thunderstorms Monday
afternoon into Monday night may contain locally heavy rain and
this could cause issues with flooding since the ground is

The boundary will remain nearby Tuesday and with plenty of
moisture in place, popup showers and thunderstorms are likely.
Again, some thunderstorms may contain gusty winds and locally
heavy rainfall. Convection should wane a bit with the loss of
daytime heating Tuesday night, but with an other cold front
approaching from the north...a few showers and thunderstorms
remain possible.


A front across the center portions of our CWA could spawn a
couple of showers and thunderstorms Wednesday into Wednesday
evening. High temperatures will be about 5 to 7 degrees above

By Wednesday overnight into Thursday, the front pushes farther
to from the north. High pressure will remain in control
Thursday night. High temperatures Thursday could be 2 to 5
degrees cooler than Wednesday, but might still be slightly above
normal for late May.

The high will move off of the coast Friday and Friday night. A
slight southerly return flow should develop and help to bring in
more humid air to our CWA. Conditions should remain dry Friday into
Friday night.

A pre-frontal trough of low pressure could develop on the
leeside of  the Potomac Highlands and over the Shenandoah
Valley Saturday. Any threat for showers and thunderstorms could
start over the Potomac Highlands before making their way east
and over the pre-frontal trough. High temperatures could be a
few degrees above normal.



VFR conditions today and tonight. A slight chance of a shower or
t-storm this afternoon, not enough coverage or confidence even
for a VCTS mention.

A weak cold front will pass through the terminals tonight, some
drier air will move in but it will not be much. With light
winds, patchy fog is possible overnight into early Monday. The
boundary will get hung up over central Virginia Monday and
return north as a warm front Monday night into Tuesday. Showers
and thunderstorms are likely near the boundary both Monday and
Tuesday. For Monday, the best chance will be near KCHO, and for
Monday night and Tuesday the best chance will be across all of
the terminals. Low clouds are possible Monday night into Tuesday
as well. Coverage of convection may wane some for Tuesday

Mainly VFR conditions Wednesday through Thursday night. Showers
and any thunderstorms could briefly reduce conditions to MVFR
or IFR Wednesday and Wednesday evening. Winds northwest 5 to 10
knots Wednesday, becoming light and variable Wednesday night and
Thursday. Winds becoming southeast 5 to 10 knots Thursday


Will continue with an SCA for the waters through today as the
gradient strengthens just a bit ahead of a cold front. The SCA
may need to be extended into this evening, but confidence is too
low at this time. A weak cold front will pass through the waters
tonight and it will stall to the south Monday before retreating
toward the waters Monday night and Tuesday as a warm front.
Showers and thunderstorms are likely ahead of the boundary,
especially Tuesday.

No marine hazards expected Wednesday through Thursday night.
Winds northwest around 10 knots Wednesday becoming light and
variable Wednesday night and Thursday. Winds veering to the
southeast around 10 knots Thursday night.


A persistent onshore flow has led to elevated water levels.

For Washington DC and Alexandria, elevated water levels will
continue through today due to freshwater coming down from the
Potomac. A Coastal Flood Warning remains in effect for
Washington DC through this evening. The highest water levels
will be around high tide this afternoon and moderate flooding is
expected. Water levels should gradually fall later tonight
through Monday, but minor flooding is still likely. A Coastal
Flood Advisory may be needed. A Coastal Flood Advisory is in
effect for Alexandria through this afternoon, and that may need
to be extended into tonight.


It has been an unusually wet pattern over the last week. For DCA
(Reagan National), there has been at least 1/4" of rain each of
the last 7 days. This is the longest streak on record. The previous
longest was 5 days in 2011, 2009, 1975, 1950, 1942, and 1937.
Precipitation records date back to 1871.


DC...Coastal Flood Warning until 10 PM EDT this evening for DCZ001.
MD...Coastal Flood Advisory until noon EDT today for MDZ014.
VA...Coastal Flood Advisory until 4 PM EDT this afternoon for
MARINE...Small Craft Advisory until 6 PM EDT this evening for


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