Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 200719

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
319 AM EDT Thu Oct 20 2016

A weak boundary overhead this morning will retreat to the north as
a warm front later today. A cold front will approach the area
tonight before passing through Friday. An upper-level trough will
pass through the area Saturday and high pressure will build into
the region for Sunday. A reinforcing cold front will pass through
the area Monday with high pressure returning for the middle
portion of next week.


A weak boundary remains draped across eastern west Virginia into
southern Maryland early this morning. A couple showers have
developed across these areas...but coverage remains isolated to
widely scattered.

The boundary will slowly lift north this morning eventually moving
off to our north today as a warm front. Southerly winds behind the
boundary will continue to usher in unseasonably warm conditions.
Max temps will be in the lower to middle 80s across most
locations. Morning clouds associated with the boundary will give
way to a partly to mostly sunny sky later today. Warm and moist
air may cause a couple popup showers to develop this afternoon.
The best chance will be across the Potomac and Allegheny Highlands
where 500mb heights are a bit lower and a weak surface trough may
develop. Even across these areas...most of the time will be dry.

A potent cold front will track through the Ohio Valley this
evening and eventually into our western areas overnight. An
upper-level disturbance associated with the boundary will remain
just to our west. Showers are expected to develop along the
boundary. The best chance for showers will be west of the Blue
Ridge Mountains after midnight.


The cold front will pass through the area from west to east Friday
morning into the midday hours. The upper-level disturbance
associated with the boundary will pass through our area during the
afternoon and evening hours. Strong PVA ahead of this system along
with mid-level frontogenetical forcing suggest that a period of
rain will likely occur behind the front during the day Friday.

Subsidence behind this system should allow for drying conditions
to move in from west to east late Friday afternoon into Friday
evening. Blustery northwest winds are expected behind the front
Friday with falling temperatures. Confidence in the Max temp
forecast is low for Friday due to uncertainty in the exact timing
of the frontal passage.

The upper-level disturbance will phase with northern stream energy
and develop into an upper-level low Friday night. This will cause
surface low pressure to rapidly intensify Friday night as it
tracks off well to our north and east. The low will move up
toward Nova Scotia Saturday into Saturday night while high
pressure approaches from the west. A northwest flow between these
systems will allow for dry and seasonably chilly conditions. A
tight gradient between the departing low and building high will
cause windy conditions during this time. The strongest winds are
expected Saturday with gusts around 40 mph possible. Winds over
the ridge tops may even be a bit higher Friday night and Saturday.

An upslope flow will likely trigger a few showers for locations
along and west of the Allegheny Front Friday night into Saturday
morning. There will be enough cold air for a few snow showers.
Snow may coat some grassy surfaces above 3kft.


High pressure will build to our south Sunday and a westerly flow
will cause more dry conditions along with sunshine. It will be
breezy as well. A reinforcing cold front will approach Sunday
night before passing through Monday. Little moisture will be
associated with this boundary so most areas may end up dry.

High pressure will return for Monday night through
Wednesday...bringing dry and chilly conditions.


A boundary remains over the region early this morning. Warm air is
overrunning this boundary and this has resulted in
clouds...especially across the northern terminals. VFR conditions
may give way to a period of MVFR conditions for a period this
morning. Confidence is low...but will continue with MVFR cigs
across the northern terminals...closer to the boundary. Patchy fog
is also expected. The best chance for fog will be across KCHO
early this morning. Have MVFR vsbys in the tafs...but IFR
conditions cannot be ruled out.

Cigs/vsbys will improve later this morning and VFR conditions are
expected this afternoon through this evening. A cold front will
approach the terminals overnight before passing through Friday.
Southerly winds and moisture ahead of the boundary may cause lower
cigs overnight into Friday morning. Showers are also likely ahead
of the front Friday morning and behind the front Friday afternoon.
A wind shift is expected from the south to the northwest behind
the boundary Friday morning....perhaps holding off until early
Friday afternoon for the eastern terminals.

Gusty northwest winds are expected behind the front later Friday
through Saturday night. The strongest winds are expected Saturday
with gusts around 30 to 35 knots possible.

VFR conditions will continue for Sunday through Monday.


A weak boundary over the waters this morning will retreat to the
north as a warm front today. Southerly winds will increase behind
the warm front this afternoon. A cold front will approach the
waters tonight into Friday morning before passing through Friday
around midday. Southerly winds will continue ahead of the front. A
Small Craft Advisory is in effect for most of the waters later
this afternoon through Friday morning. Did leave out the Upper
Tidal Potomac for now thinking that the stronger wind field aloft
may hold off until after peak mixing.

Gusty northwest winds will develop behind the boundary Friday
afternoon. A Small Craft Advisory is in effect for all of the
waters. More gusty winds are expected Friday night through
Saturday night. A Small Craft Advisory will be needed and a Gale
Warning may be needed for portions of the waters during this time.

High pressure will build to the south of the water Sunday before
another cold front passes through Monday. High pressure will build
in for the middle portion of next week. A Small Craft Advisory may
be needed for portions of the waters during this time.


The light onshore flow has led to elevated water levels.
However...water levels are expected to remain below minor flood
thresholds through this afternoon since the next high tide will be
the lower of the two.

Southerly winds will increase later this afternoon and continue
through tonight. Tidal Anomalies are expected to increase during
this time and this may cause minor flooding for sensitive areas
during the high tide cycle tonight. Elevated water levels will
continue into Friday morning before gusty northwest winds develop
Friday afternoon.

Blowout tides are possible Friday night through Saturday night due
to a strong offshore flow.


Records for Wednesday were broken at Dulles and BWI airports. A
record high minimum was set for Reagan National on Wednesday
as well. See RER reports for details. Near record warmth is
expected again today.

Below is a list of record daily warm temperatures for October

Record daily high temperatures
Site    10/20
DCA    86 (1969)
BWI    87 (1969)
IAD    83 (1969)
*also occurred in previous years

Record daily warm low temperatures
Site    10/20
DCA    64 (1885)*
BWI    65 (1910)
IAD    59 (1993)
*also occurred in previous years


MARINE...Small Craft Advisory from 2 PM this afternoon to 6 PM EDT
     Friday for ANZ530>534-536>543.
     Small Craft Advisory from noon to 6 PM EDT Friday for ANZ535.


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