Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 190729
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
329 AM EDT Sat Aug 19 2017

.SYNOPSIS...
Weak high pressure will build in today...but an upper-level
disturbance and reinforcing cold front will pass through the
area this evening. High pressure will build overhead late
tonight through Sunday before moving offshore Monday. High
pressure will remain offshore Tuesday and a stronger cold front
will pass through Wednesday.

&&

.NEAR TERM /THROUGH TONIGHT/...
A cold front will continue to move off to the east early this
morning. An upper-level disturbance will also pass through the
area early this morning. There will be enough moisture for a
couple popup showers across the Virginia Piedmont into central
and southern Maryland...where there is a little more moisture.

Drier air will continue to move into the region later this
morning into this afternoon from the northwest behind the cold
front and also behind the upper-level disturbance. More warm
conditions are expected...but it will be noticeably less humid
compared to Friday along with some sunshine. Max temps will be
in the upper 80s to lower 90s across most locations.

Another upper-level disturbance and its associated cold front
will approach the area late this afternoon before passing
through this evening. Most of the forcing from the upper-level
disturbance will be to the north and forcing along the cold
front will be weak. A few popup showers and perhaps even an
isolated thunderstorm are possible across northern and central
portions of the CWA late this afternoon through this evening.
Coverage should remain isolated to scattered and much of the
time will turn out dry.

The weak cold front will move off to the east late tonight and
high pressure will return...bringing dry conditions. Min temps
will be range from the 50s in the Allegheny Highlands to near 70
in downtown Washington and Baltimore. Dewpoints in the 50s and
60s will make it feel more comfortable compared to recent
nights.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
High pressure will remain over the region Sunday...bringing dry
conditions along with sunshine. More seasonably warm conditions
are expected...but humidity will remain on the low side with
dewpoints in the low to mid 60s for most areas.

Surface high pressure will remain overhead Sunday night...but a
return flow at the low-levels will allow for warm and moist air
to overrun the relatively cooler surface air. This will bring
more clouds. An isolated shower cannot be ruled out...but most
areas should be dry.

The surface high will move offshore Monday and a southerly flow
will allow for more humid conditions to return. At the same
time...there may be a couple upper-level disturbances that pass
through the area in the zonal flow aloft. A few showers and
thunderstorms are possible...especially during the later
afternoon and evening hours due to more instability and forcing
from a surface trough and upper-level disturbances. Still some
uncertainty as to how much moisture makes its way back into the
region...but instability may be on the high side which could
cause some stronger or locally severe storms. Confidence is low
at this time.

As for clouds...there may be a bkn/ovc deck around
5 to 10kt feet from isentropic lift to start the morning. Do
think the isentropic lift will dissipate some and this should
allow for breaks of sunshine during the late morning into the
afternoon hours. Then...more clouds are likely with any
thunderstorms later in the day. Therefore...the most likely sky
cover during the solar eclipse will be partly sunny.

A southerly flow will continue Monday night...bringing very warm
and humid conditions.


&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
High pressure will remain over the Atlantic while a cold front
approaches from the north and west Tuesday. More very warm and
humid conditions are expected ahead of the boundary. Showers and
thunderstorms are also possible ahead of the
boundary...especially Tuesday afternoon into Tuesday night. Some
storms may become strong to severe due to strengthening shear
profiles associated with the upper-level trough that will be
digging from the Great Lakes into New England.

The cold front will pass through Wednesday. A few more showers
and thunderstorms are possible...but confidence is low due to a
downsloping westerly flow that may develop behind a pressure
trough and ahead of the cold front. High pressure will build
toward the area Wednesday night through Friday while an upper-
level trough digs south from the Great Lakes over our area. A
northwest flow will usher in much cooler and less humid
conditions compared to recent days. Highs in the 70s to lower
80s with lows in the 50s and 60s will make it feel more like mid
to late September instead of August.

&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
VFR conditions are expected most of the time through Wednesday.
Patchy fog cannot be ruled out early this morning. An isolated
shower or thunderstorm is possible late this afternoon and
evening across the northern terminals...but most areas will be
dry.

Scattered thunderstorms are possible later Monday into Monday
night as a southerly flow allow for more atmospheric moisture to
return. A cold front will approach Tuesday before passing
through Wednesday. Showers and thunderstorms are possible ahead
of the boundary. Some thunderstorms may become strong to locally
severe during the early and middle portions of next week.
Confidence remains low at this time.

&&

.MARINE...
A weak cold front will continue to move off to the east early
this morning. Will continue with the SCA for most of the Bay and
lower Tidal Potomac river...but it will be marginal with gusts
around 18 to 20 knots. Another reinforcing cold front will pass
through the waters this evening. A popup shower cannot be ruled
out but most areas will be dry.

High pressure will build overhead for Sunday before moving
offshore Monday. A return southerly flow will develop Monday and
persist through Tuesday night ahead of a cold front. Winds will
turn to the northwest behind the cold front Wednesday. A Small
Craft Advisory may be needed for Monday night and Tuesday and it
will likely be needed Wednesday into Wednesday night behind the
cold front.

&&

.TIDES/COASTAL FLOODING...
Elevated water levels remain and a coastal flood advisory is in
effect for Annapolis in Anne Arundel County. An offshore flow
will develop behind a cold front early this morning. This should
allow for anomalies to decrease a bit today. Another reinforcing
cold front will pass through tonight and an offshore flow will
develop behind that boundary late tonight into Sunday.
Therefore...minor flooding is not forecast at this time.
However...it will be close for sensitive areas because the
offshore flow will be weak and we are approaching a new moon
phase which means astronomical norms will be higher during the
preferred high tide. Therefore...we will have to keep a close
eye on anomalies late tonight into early Sunday.

A southerly flow will increase early next week and this may
cause minor flooding near high tide for sensitive areas Monday
night into Tuesday.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Coastal Flood Advisory until 7 AM EDT this morning for MDZ014.
VA...None.
WV...None.
MARINE...Small Craft Advisory until 9 AM EDT this morning for
     ANZ531>534-537-539>541-543.

&&

$$
SYNOPSIS...BJL
NEAR TERM...BJL
SHORT TERM...BJL
LONG TERM...BJL
AVIATION...BJL
MARINE...BJL
TIDES/COASTAL FLOODING...BJL


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