Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 171852

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
252 PM EDT Sat Jun 17 2017

A very warm and moist 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
next week.


Low clouds have given way to some sunshine as the nocturnal
inversion has mixed out.

Plenty of moisture remains in place with dewpoints in the upper
60s and lower 70s for most locations. A southerly flow has
ushered in warm and humid conditions. Latest mesoanalysis shows
PWATS ranging between 1.5 inches near the Potomac Highlands to
near 2 inches east of the Blue Ridge Mountains. The breaks of
sunshine have lead to an unstable atmosphere with around
500-1000 J/KG of MLCAPE. A few popup showers have developed
early this afternoon as the capping inversion breaks. Additional
popup showers and thunderstorms are expected later this
afternoon into this evening. Pinpointing exactly when and where
convection will occur is more difficult since there is a lack of
a strong lifting mechanism.

Convection will dissipate after sunset due to the loss of
daytime heating. A southerly flow will continue tonight and
this will allow for more warm and humid conditions. Areas of low
clouds and fog are expected overnight.


A cold front will move through the Midwest and into the Ohio
Valley Sunday. Somewhat drier air aloft and a stronger capping
inversion will allow for more sunshine Sunday after low clouds
and fog burn off. A south to southwest flow along with more
sunshine will cause hot and humid conditions with max temps in
the upper 80s and lower 90s across most locations. The hot and
humid conditions will lead to an unstable atmosphere. The heat
and humidity should be enough to break the capping inversion
during the afternoon and evening hours. Isolated to scattered
thunderstorms are expected. Coverage may not be as widespread as
recent days...but shear profiles will be noticeably stronger.
Therefore...a few thunderstorms may become severe especially
west of the Blue Ridge Mountains where 500mb heights will be a
bit lower and shear will be strongest.

The cold front over the Ohio Valley will approach western
portions of the CWA Sunday night. Additional showers and
thunderstorms are possible ahead of the boundary...especially
across western portions of the CWA. More warm and humid
conditions are expected Sunday night ahead of the boundary.

The cold front will slowly pass through the area Monday into
Monday night. Shear profiles will continue to strengthen as the
upper-level trough associated with the cold front digs over the
Ohio Valley and Midwest. A south to southwest flow ahead of the
cold front will continue to usher in very warm and humid
conditions. The unstable atmosphere...along with forcing from
the cold front will lead to showers and thunderstorms. Strong
shear profiles suggest that there is an enhanced threat for
severe thunderstorms with damaging winds being the primary
threats due to unidirectional winds with height. Copious amounts
of moisture will also cause thunderstorms to contain heavy
rainfall. A shear vector nearly parallel to the cold front
suggests that training convection is possible. This elevates the
threat for flash flooding despite the faster storm motion
expected. The best chance for severe storms with heavy rain will
be during the afternoon and evening hours east of the Allegheny
and Potomac Highlands.

The cold front will move off to the east by Tuesday morning and
convection should dissipate overnight behind the boundary.


Weak high pressure will build toward the region Tuesday and
Wednesday while an upper-level trough builds overhead. Drier and
less humid conditions are expected along with seasonably warm
temperatures. A couple popup showers and thunderstorms cannot be
ruled out though due to the upper-level trough overhead.

A nearly zonal flow aloft develops Thursday through Saturday.
Most of the jet energy should remain to our north...which puts
our area on the warm side of a nearly stationary to our north.
More hot and humid conditions are possible along with increasing
chances for showers and thunderstorms.


Popup showers and thunderstorms are expected this afternoon into
this evening. Coverage will dissipate after sunset. More low
clouds and areas of fog are expected late tonight into early

A cold front will approach from the west Sunday. A few showers
and thunderstorms are possible during the afternoon hours into
Sunday night. The cold front will pass through Monday and there
is a better chance for showers and thunderstorms. Some
thunderstorms may be severe. Weak high pressure will build over
the terminals during the middle portion of next week.


A southerly flow will strengthen this afternoon into tonight. A
Small Craft Advisory is in effect for the Bay and lower Tidal
Potomac River. Will have to watch the upper portions of the
Potomac River for a few hours late this afternoon and early this
evening. Did not include in the SCA since the wind field may not
increase until after peak mixing for these areas.

A cold front will approach the waters Sunday and Monday before
passing through Monday night. South to southwest winds will
increase during this time. A Small Craft Advisory is in effect
for the waters Sunday night and will likely need to be extended
into Monday and Monday night.

Popup showers and thunderstorms are expected this afternoon and
evening...then again Sunday afternoon and evening. Locally gusty
winds are possible in stronger thunderstorms. More widespread
thunderstorms are expected later Monday into Monday night.
Severe thunderstorms are possible during this time with damaging
winds being the primary threat.

Weak high pressure may build over the waters behind the boundary
for the the middle portion of next week...but the boundary will
stall out nearby.


A southerly flow has developed over the waters today. Tidal
anomalies are around one foot above astronomical norms. The
southerly flow is expected to strengthen through tonight and the
southerly flow is expected to continue through Monday. Tidal
anomalies will likely increase a bit in response to the
strengthening flow.

Minor tidal flooding is likely for Straits Point and Annapolis
with the high tide cycle tonight. A Coastal Flood Advisory is
in effect for St Marys County and Anne Arundel Counties. Minor
tidal flooding is possible with the high tide cycle tonight for
other sensitive locations...but confidence is too low for an
advisory at this time. Minor flooding is also possible Sunday
and Monday as the southerly flow continues.


MD...Coastal Flood Advisory from 7 PM to 11 PM EDT this evening for
MARINE...Small Craft Advisory from 5 PM this afternoon to 6 AM EDT
     Monday for ANZ530>532-538>540-542.
     Small Craft Advisory until 6 AM EDT Monday for ANZ533-534-537-
     Small Craft Advisory from noon Sunday to 6 AM EDT Monday for


TIDES/COASTAL FLOODING...BJL is the U.S. government's official web portal to all federal, state and local government web resources and services.