Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 211438

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1038 AM EDT Fri Oct 21 2016

A cold front will pass through the region today. 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.


The cold front is pushing through the Highlands as of mid-morning.
Narrow band of low topped convection is accompanying the front,
with a few gusts of 30-40 MPH observed. HRRR continue to shows
lightning possible as the line pushes east of the Blue Ridge this
afternoon, although poor lapse rates above 15kft should limit both
lightning and any potential of severe-level wind gusts. Morning
update largely focused in refreshing timing of all elements as the
front passes. Otherwise, the previous thinking is largely on
track. POPs have been tapered more slowly this evening due to the
HRRR/RAP showing better shower potential with the vort max. We
may need to consider both wind and freeze products for the
Highlands tonight.

Previous discussion:

The cold front will make its way through the Washington and
Baltimore Metropolitan areas between 1 and 4 pm this afternoon.
The cold front will pass through the Bay late this afternoon.
Showers are likely along and just ahead of the boundary as it
moves through the area. More showers are possible behind the cold
front as a potent upper-level disturbance pass through the region.
Confidence in max temp forecast is low since it will be highly
dependent on the timing of the frontal passage. Max temps are
forecast to range from the mid to upper 50s in the Allegheny the upper 60s and lower 70s for valley locations
west of the Blue Ridge the upper 70s and lower 80s
near Washington and Baltimore into southern Maryland. Temperatures
are expected to drop quickly behind the cold front...into the 40s
and 50s this afternoon west of the Blue Ridge Mountains and into
the 50s and 60s east of the Blue Ridge Mountains by late this

The cold front will move off to the east this evening and the
upper-level disturbance associated with the boundary will pass
through during this time. Blustery northwest winds are also
expected behind the front and this will cause temperatures to
continue falling. A few showers are possible due to the passing of
the upper-level disturbance...but precipitation amounts will be

The upper-level disturbance will develop into a closed upper-level
low overnight and the upper-level trough overhead will shift to a
negative tilt. This will cause surface low pressure to rapidly
intensify off to our north and east. A strengthening pressure
gradient will cause gusty northwest winds overnight. Wind gusts
around 50 mph are possible along the ridges of the Allegheny and
Potomac Highlands as well as the Blue Ridge and Catoctin
Mountains. A wind advisory may be needed for these areas.
Elsewhere...frequent gusts around 30 mph are expected. The
northwest flow will dry things out across most areas...but a few
rain/snow showers are possible along the ridge tops along and west
of the Allegheny Front. Snow may coat grassy surfaces above 3kft.
A freeze is possible overnight across the ridge tops of the
Allegheny and Potomac Highlands...mainly above 3kft.


Low pressure will continue to intensify as it tracks northward
into Ontario Saturday. High pressure will remain over the MIdwest
into the Gulf Coast States. A tight gradient between the departing
low and the building high will continue to cause windy conditions.
Cold advection will increase wind gusts around 35 to
45 mph are expected. A wind advisory may be needed for portions of
the area. The best chance for wind gusts around 50 mph will be
along the ridges. Max temps Saturday will be much chillier due to
the northwest flow...ranging from the 40s in the mountains to the
upper 50s and lower 60s near Washington and Baltimore into
southern Maryland.

High pressure will build to our south Saturday night through
Sunday. Breezy conditions along with mainly clear skies are
expected. Sunday may be a bit milder due to a downsloping westerly
flow with highs in the 60s across most areas. A reinforcing cold
front will approach Sunday night...but it should remain to our
north. More dry and seasonable conditions are expected.


A reinforcing cold front will cross the area on Monday. GFS/ECMWF
timing differ a bit.  Splitting the difference suggests it may be a
morning fropa. Although moisture and upper level energy remain to
the northeast of the forecast area, nearer the lower heights in the
base of the trough axis, cold advection will sweep the area during
the day. As a result, the frontal passage should be dry, with
perhaps a few more clouds. After that, expect mostly sunny and
breezy conditions.

It may be difficult to get frost Monday night due to a breeze
(there`s still room for that to change), but temperatures should
drop into the 30s in the mountains, lower-mid 40s elsewhere. After a
day in the mid 50s-lower 60s Tuesday, radiational cooling should be
better Tuesday night as the center of high pressure builds toward
the Mid Atlantic. This may spell the end of the growing season for
outlying/rural areas.

The next storm system will be cutting across the Ohio Valley toward
the Great Lakes toward midweek. While is should stay north/west of
the area, its attendant cold front will approach by Thursday,
potentially bringing showers back to the area.


A southerly flow will continue to ahead of a cold front through
this morning. Narrow band of MVFR/IFR cigs east of the Blue Ridge
is beginning to break up per visible satellite. However, low
confidence on whether this deck fully lifts before fropa.

A cold front will pass through the terminals...across KMRB
before noon...then across the rest of the terminals between 1 pm
and 4 pm. A wind shift to the northwest is expected behind the
front with gusts around 20 to 25 knots likely. A narrow line of
showers also may produce gusts of 30 kt and isolated lightning
east of the Blue Ridge. Showers may hang around into this evening
as an upper-level disturbance passes through. MVFR conditions are
possible in showers today.

Gusty northwest winds will continue through Saturday evening. The
highest gusts are expected Saturday when mixing will be strongest.
Gusts around 35 knots are likely. Winds will diminish Saturday
night...but breezy conditions will continue through Sunday as high
pressure settles to the south.

VFR conditions should prevail Monday-Tuesday. Could have some gusty
northwest winds on Monday behind a cold front.


A southerly flow will continue through early this afternoon ahead
of a cold front. Will continue with the Small Craft Advisory...but
it will be marginal. The cold front will pass through the waters
between 2 and 5 pm this afternoon. A wind shift to the northwest
is expected behind the boundary and winds will become gusty. A
line of showers will accompany the front. While most wind gusts
should be 20-30 kt, can`t rule out higher gusts, especially if
thunder is able to develop. Since the synoptic gale isn`t expected
until much later, these showers/storms could require Special
Marine Warnings.

Winds will increase as the pressure gradient strengthens tonight
through Saturday. A Gale Warning is in effect for the Bay and
lower tidal Potomac River tonight...and for all the waters
Saturday. The strongest winds are expected Saturday. Winds will
diminish a bit Saturday night...but a Small Craft Advisory will
likely be needed. More breezy conditions are expected Sunday into
Sunday night.

A cold front will cross the waters on Monday. Small Craft
Advisories seem likely from this vantage point behind the cold
front. Winds will be diminishing on Tuesday as the pressure
gradient relaxes.


A south to southeast flow has caused tidal anomalies to increase
quickly this morning. Anomalies are still increasing to around 1
to 1.5 feet above normal this morning as the south to southeast
flow continues. A Coastal Flood Advisory is in effect for Anne
Arundel County with the current high tide. Minor flooding is
possible around high tide early this afternoon near Washington DC.
Will have to monitor anomalies this morning. South to southeast
winds will continue through early this afternoon before turning
quickly to the northwest by the end of the day. Minor flooding is
possible during the high tide cycle late this afternoon into this
evening...but confidence is low because of the northwest flow that
will be developing during this time.

Anomalies will drop sharply tonight and blowout tides are possible
for Saturday due to a strong northwest flow.


Record high minimum temperatures were set at DCA...BWI...and IAD
Thursday...October 20th. See the latest RER for more details. The
passage of a cold front should prevent records from being reached
once again today.

Records for Oct 21st...
DCA...High 85 in 1947...warm low 64 in 1984.
BWI...High 90 in 1947...warm low 63 in 1947.
IAD...High 86 in 1979...warm low 60 in 1979.


MD...Coastal Flood Advisory until noon EDT today for MDZ014.
MARINE...Small Craft Advisory until 6 PM EDT this evening for
     Gale Warning from 6 PM this evening to 6 PM EDT Saturday for
     Small Craft Advisory until 6 AM EDT Saturday for ANZ535.
     Gale Warning from 6 AM to 6 PM EDT Saturday for ANZ535-536.
     Small Craft Advisory until 6 AM EDT Saturday for ANZ536.


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