Area Forecast Discussion
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FXUS61 KLWX 190129
Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
929 PM EDT Tue Oct 18 2016
High pressure in the western Atlantic will remain in place for
the next several days. A cold front will slide southward toward
the area Wednesday before lifting back north Thursday. Another,
stronger cold front will cross the region Friday. High pressure
will return for the weekend.
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
High pressure remains centered off the coast this evening. A cold
front extends through Lakes Ontario and Erie. Prefrontal clouds
are quickly approaching from the NW, although showers are confined
closer to the front at this time. The cloud band will slow down
however, only affecting northern and western sections of the
area overnight. Some of the showers could reach the Allegheny
Plateau later tonight, but have trouble advancing to the leeward
The best chance for patchy fog tonight remains across the
Shenandoah Valley and Central Foothills/Piedmont, as they should
be mostly clear. Southerly flow may be slightly greater tonight
and therefore patchy fog should be confined to river and sheltered
One difference tonight than the past couple is a slower fall in
temperatures, with locations that haven`t decoupled still well
into the 70s. Will adjust temperatures based on latest trends, but
local results may vary depending on decoupling and the advancing
clouds. Lows will be in the 60s for most though.
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
The cold front will be in vicinity of the northern Mid-Atlantic
region on Wednesday, before lifting back north early Thursday.
This will result in overrunning across the region and showers will
be possible. While the greatest chance of showers (although
scattered at best) will remain in the Highlands and north of
I-66/US-50 through Wednesday night, 18Z guidance trended a bit
south with shower chances. 12Z SSEO keys in on the east side of
the Blue Ridge, although it may be too ambitious trying to produce
convection, which seems unlikely given a stable layer around 12kft
in forecast soundings. Have therefore only made small increases
in POPs. Southerly flow will continue across much of the region
and temperatures are expected to climb into the 80s again, however
more cloud cover will result in temperatures lower than Tuesday.
A strong cold front approaches from the west on Thursday. Mid-
level flow will increase across the region and will advect in more
moisture from the south. Coverage of showers will increase from
west to east Thursday night as a cold front approaches the
mountains. Rainfall amounts of less than a quarter inch are
expected with the highest amounts across the highlands. There may
also be isolated embedded thunder, mainly far western areas.
.LONG TERM /FRIDAY THROUGH TUESDAY/...
Guidance is still a bit uncertain about timing of the strong cold
frontal passage on Friday but overall they are coming into better
agreement with the faster ECMWF timing than they were previously.
The ECMWF brings the front through during the day Friday with some
showers and perhaps a thunderstorm. Still some more details to be
worked out but definitely becoming cooler later in the day behind
the front as well as pretty breezy.
The rest of the long term period will be dominated by a deep trough
which will persist just to our north or northeast through Tuesday.
This will keep fast west or northwest flow across the region aloft
with much cooler conditions compared to the short term. Highs may be
stuck in the 50s some days and frost/freeze is not out of the
question if high pressure and calm winds coincides with a night
period. This is hard to time since a weak reinforcing cold front
will be in the mix which may pass at a bad time for radiational
cooling to maximize.
.AVIATION /01Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions will continue into tonight. Patchy fog possible again
overnight mainly at CHO/IAD, with MRB depending on advancing cloud
cover. LAMP points to IFR at CHO, but have limited to MVFR in the
TAF due to poor performance last night and less favorable
A stalled frontal boundary will be across the
region Wednesday night into Thursday and lower cigs will be
possible, however flight restrictions are not expected at this
time. The position of the front is a little questionable, but
looking like the northern TAF sites will obtain a NW or N wind by
late Wednesday. Showers increase in coverage Thursday night and
sub- VFR conditions are possible into Friday.
Sub-VFR expected at times Friday as a cold front moving through the
region brings showers and wind gusts up to 35 knots or so. Winds may
persist at times Friday night and Saturday but cigs and vis likely
to return to VFR. VFR overall though Sunday-Tuesday but a cold front
moving through Monday or Tuesday may briefly feature a reduction to
MVFR with more showers at some point. Timing on this feature is
Southerly winds will continue on the waters tonight, around 10 kt
or less. A front will stall and bisect the waters on Wednesday,
before lifting north on Thursday morning; therefore winds will be
variable but less than SCA criteria. Winds increase a bit out of
the south Thursday night ahead of an approaching frontal system
and winds may approach SCA conditions.
Cold front moving through the region Friday will very likely bring
SCA conditions with gales possible later Friday into early Saturday.
Winds should relax late in the weekend into early next week as high
pressure builds over the region.
A south to southwest flow will continue over the waters through
Wednesday night. Southerly winds are most likely Thursday into
Friday ahead of a cold front. Elevated water levels are expected
during this time.
DC/Alexandria are trending to peak just below minor flood
thresholds for this evening`s high tide, so am holding off on an
advisory. Water levels will need to continue to be monitored over
the next several days, with the PM high tide being the favored
cycle for nearing minor flood threshold at sensitive sites.
A potent offshore flow will develop behind a cold front later
Friday through the weekend. Blowout tides are possible during this
A record daily high temperature of 84 degrees was set at
Baltimore-Washington International Thurgood Marshall Airport (BWI)
near Baltimore MD Tuesday. This breaks the old record of 82 set
in 1945...1928 and 1908.
Climate records have been kept at BWI since 1950. Additional
temperature records for the Baltimore MD area extend back to
July of 1872.
Two record daily high temperatures were set at Washington Dulles
International Airport (IAD) so far this week. A high temperature of
84 degrees Monday broke the old record of 83 set in 1963. A high of
85 degrees on Tuesday broke the old record of 82 set in 2007 and
Climate records have been kept at IAD since November of 1962.
Below is a list of record daily warm temperatures for October
19th and 20th.
Record daily high temperatures
Site 10/19 10/20
DCA 88 (1938) 86 (1969)
BWI 82 (1947)* 87 (1969)
IAD 83 (1991)* 83 (1969)
*also occurred in previous years
Record daily warm low temperatures
Site 10/19 10/20
DCA 65 (1905) 64 (1885)*
BWI 67 (1905) 65 (1910)
IAD 60 (2011) 59 (1993)
*also occurred in previous years