Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 210739

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
339 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.


A cold front is moving through West Virginia early this morning
while the mid-level trough axis associated with the boundary is
passing through the Ohio Valley. A southerly flow ahead of the
boundary has allowed for unusually warm conditions early this

The cold front is expected to pass through the area today. The
boundary will pass through the Potomac Highlands by mid-
morning before making 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 afternoon.

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 o
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 southeast flow will continue to ahead of a cold front through
this morning. Cigs may drop to MVFR/IFR levels during this
time...but confidence is low. Do feel that if cigs do drop MVFR
conditions are more likely vs. IFR since there is some wind
underneath the inversion.

A cold front will pass through the terminals...first across KMRB
between 10 am and 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. Showers
are also expected with the frontal passage and a few 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.

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. Latest anomalies are around 0.75-1.25 feet
above normal. The south to southeast flow is expected to continue
through early this afternoon before turning quickly to the
northwest by the end of the day. Despite the next tide being the
lower of the two...minor flooding is possible for sensitive areas
especially around Annapolis and Straits Point. Will continue to
monitor anomalies this morning to see if an advisory is needed.

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.


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 from noon today to 6 AM EDT Saturday for
     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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