Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 030210 AAB
AFDLWX

Area Forecast Discussion...UPDATED
National Weather Service Baltimore MD/Washington DC
910 PM EST Fri Dec 2 2016

.SYNOPSIS...
High pressure will gradually move into the region through Sunday.
An upper-level disturbance will pass through the area Sunday night
and high pressure will briefly return for Monday. Coastal low
pressure will impact the area Tuesday before high pressure
briefly returns for Wednesday. A potent cold front will move
through late next week.

&&

.NEAR TERM /THROUGH SATURDAY NIGHT/...
Have gotten a few reports of freezing drizzle and light snow
creating slick roads at high elevations across the Potomac
Highlands. Shallow moisture profiles should keep accumulations
light...but temperatures in the M20s/L30s are creating hazardous
travel conditions in spots. Thus, a Winter Weather Advisory is in
effect until 6 AM to account for the combination of freezing
drizzle and light snow. Winds could also gust up to 40 mph across
the ridgetops.

Elsewhere...expect breezy conditions to continue through the
overnight...especially across the northern half of the area. Low`s
generally in the 20s to low 30s outside of the DC/Balt
metros...where mid/upper 30s will be more common.

Previous Discussion...
Latest surface analysis shows high pressure stretching from North
Dakota southeast to Alabama, with a low pressure centered just
northwest of Caribou Maine. This puts our region in a steady NW
flow which should continue through Saturday as both the high and
low very gradually shift eastward. By Saturday night, the high
pressure ridge to our west finally starts to move overhead and the
winds should relax. Aloft, the NW flow will be enhanced by a
passing shortwave later tonight before a ridge to the west starts
building in Saturday night. The NW flow will remain fairly moist
so expect skies to remain at least partly cloudy for much of the
area this evening, perhaps clear a bit later tonight though some
clouds may redevelop with the sunshine on Saturday. Most of the
region should stay dry, but the moist NW flow will bring some snow
showers with minimal if any accumulations to the Allegany Front.
Meanwhile, we`ll also have some high clouds overhead especially
later Saturday and Saturday night, so not really expecting a sunny
start to the weekend. With wind do not expect it to get very cold
tonight but temps will stay a bit lower tomorrow compared to today
with cold advection ongoing. Better chance of radiational cooling
on Saturday night with the high pressure ridge moving overhead and
winds decreasing, but increasing high clouds may counteract that.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY/...
Sunday the ridge passes east as a shortwave trough approaches from
the west. This system has minimal surface reflection but warm air
advection will allow clouds to dominate. The clouds will keep
temps in the 40s in most spots. By Sunday night, there looks like
enough forcing may be present for some light precipitation, though
given the upper level pattern its certainly possible that most
precip splits around us. Looking at latest guidance, most likely
the metro area on S and E will end up with just plain rain,
though N and W some snow is possible, especially across the higher
terrain since lowest levels will be notably warmer. Guidance still
wavers a bit on amounts, with the latest ECMWF notably wetter than
the GFS. Given relatively warm antecedent conditions, any
accumulations where it does snow would likely be limited to
higher elevations, with valleys even all the way up to Hagerstown
likely to struggle to accumulate any snow even if snow does make
it to the surface. Lows on Sunday night will be in the 30s. Weak
ridging returns on Monday with just some clouds and slightly
warmer temps, with highs getting back into the 50s in parts of the
area.

&&

.LONG TERM /MONDAY NIGHT THROUGH FRIDAY/...
Two main weather producers in the extended part of the forecast -
a short wave Tuesday and a long wave late Thursday into Friday.
GFS/Euro in agreement regarding the short wave moving out of the
TN valley Tuesday morning...reaching the coast that evening. There
will be a relative paucity of cold air as the wave approaches -
Euro 850- 1000 thickness for Tuesday is currently AOA 1300 DM.
It`s a long way out to try to get into specifics...but perhaps a
wintry mix west of I-81 overnight then rain over the area for
several hours Tuesday. This looks to be a fairly fast mover so no
drought breaker.

Highs Tuesday expected to reach mid 40s.

Cold air will remain at bay during midweek. Larger long wave
takes shape over the Rocky Mountains which will cause upper level
flow in the Mid Atlantic to be from the southwest. Highs should be
in the upper 40s to mid 50s. Lows in the mid 30s.

It`s a week away but the second weather maker - the long wave,
will likely be affecting the region Thursday bringing the chance
of rain showers to the forecast area through Thursday night. Lows
Wednesday night in the mid to upper 30s. Highs Thursday upper
40s/lower 50s. Cooler air moves into the area Thursday night as
precip ends...lows in the 20s.

&&

.AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
VFR likely thru late Sunday with high pressure crossing the area.
Some clouds at 4-5kft expected through Saturday, then just high
clouds Saturday night and much of Sunday before cigs lower again.
No vis restrictions thru Sunday afternoon with no precip or fog
expected. Winds should abate some tonight before before re-firing
Saturday. Lighter winds expected Sunday.

Weak system moving in on Sunday night may reduce cigs and vis to
MVFR or even perhaps IFR briefly. Precip most likely rain but a
little snow could mix in at MRB. Returning to VFR Monday behind
this system. Ceilings could drop into MVFR range Tuesday ahead of
a fast moving system.

&&

.MARINE...
SCA for all waters thru Saturday, then gradually dying off
Saturday night as gradient relaxes under high pressure. Winds aloft
increases tonight into Saturday and if there is enough mixing with
the colder air moving over the warmer water, we may briefly reach gale
gusts. Uncertainty remains very high given its likely to be
marginal if it even happens so have not raised gales yet. Best
chance would be later tonight into early Saturday. Otherwise dry
conditions expected thru Sunday. Sub SCA winds expected Sunday
night into Monday as a weak system passes with a little rain.
Chances of rain Tuesday although winds still expected to remain
below SCA values.

&&

.CLIMATE...
Meteorological autumn 2016 has ended (it runs from September 1st
through November 30th). It was unusually warm and dry across the
much of the area. Below are preliminary temperature and
precipitation rankings for this autumn.

Washington DC area (Ronald Reagan National Airport, DCA)
Temperature (warmest)     Precipitation (driest)
1.  63.9 degrees (2016)   1.  1.83 inches (1930)
2.  63.3 degrees (2007)   2.  2.42 inches (1941)
                          3.  2.65 inches (2001)
                          4.  3.33 inches (1998)
                          5.  3.45 inches (1879)
                          6.  4.07 inches (1967)
                          7.  4.16 inches (2016)
                          8.  4.26 inches (1973)
Records have been kept at DCA since August 1st 1941. Additional
temperature records in the Washington DC area date back to 1872,
and additional precipitation records date back to 1871.

Baltimore MD area (Baltimore-Washington International Thurgood
Marshall Airport, BWI)
Temperature (warmest)     Precipitation (driest)
1.  64.7 degrees (1931)   Not in Top 20 (2016 was 29th driest
2.  63.4 degrees (1941)   with 6.65 inches)
3.  63.3 degrees (1881)
4.  61.9 degrees (1946)
5.  61.8 degrees (1900)
6.  61.3 degrees (1970)
7.  61.1 degrees (1927)
8.  60.7 degrees (1947)*
9.  60.4 degrees (1930)
10. 60.3 degrees (1919)
    60.3 degrees (1945)
    60.3 degrees (1942)
13. 60.2 degrees (2016)
    60.2 degrees (1985)
*One day of missing data
Records have been kept at BWI since January 1st 1950. Additional
temperature records in the Baltimore MD area date back to 1872,
and additional precipitation records date back to 1871.

Dulles VA area (Washington Dulles International Airport, IAD)
Temperature (warmest)     Precipitation (driest)
1.  60.3 degrees (2007)   1.  3.96 inches (1998)
2.  60.0 degrees (2016)   2.  4.59 inches (1978)
3.  59.5 degrees (1985)   3.  4.61 inches (1965)
                          4.  4.97 inches (2016)
                          5.  5.31 inches (1981)
Records have been kept at IAD since November 30th 1962.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Winter Weather Advisory until 6 AM EST Saturday for MDZ501.
VA...Winter Weather Advisory until 6 AM EST Saturday for VAZ503.
WV...Winter Weather Advisory until 6 AM EST Saturday for WVZ501-503-
     505.
MARINE...Small Craft Advisory until midnight EST Saturday night for
     ANZ531-532-538>540.
     Small Craft Advisory until 6 PM EST Saturday for ANZ530-535-
     536-542.
     Small Craft Advisory until 6 AM EST Sunday for ANZ533-534-537-
     541-543.

&&

$$
SYNOPSIS...RCM
NEAR TERM...MSE/RCM
SHORT TERM...RCM
LONG TERM...ABW
AVIATION...RCM/ABW
MARINE...RCM/ABW
CLIMATE...DFH



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