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000
FXUS61 KLWX 100153
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
853 PM EST Sun Dec 9 2018

.SYNOPSIS...
Low pressure will pull away from the Carolina coast tonight. A
second area of low pressure will develop offshore of the
Carolinas Monday then move out to sea as high pressure builds in
from the Ohio Valley. This area of high pressure will retreat to
offshore of New England through the end of the week as a large
area of low pressure develops over the Tennessee Valley and
heads toward the region.

&&

.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
Low pressure now resides off the coast of Cape Hatteras with the
snow band now weakening and shrinking back off to the south/east
across the region. Also seeing reports of rain/sleet/freezing
rain mixing in with the snow as warming occurs aloft, and this
is also confirmed by dual-pol radar signatures. Thus have begun
the process of trimming back the ongoing warnings/advisories to
where accumulating snow is still occurring, and will likely be
able to trim further over the next 1-3 hours, with all areas
ending by midnight.

Low pressure will then pull away tonight, with snow coming to
an end across all areas by midnight.

Low temperatures tonight will remain below normal, generally
from the upper teens to upper 20s. Skies should begin to clear
to the northwest very late.

&&

.SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
A secondary northern stream shortwave will dive to our south
Monday, with surface low pressure developing off the Carolina
coast and heading out to sea. No impact is expected locally from
this system.

High pressure will follow, building in from the Ohio Valley into
Tuesday. Multiple shortwaves aloft will begin approaching from
the west well out ahead of long wave troughing deepening over
the central U.S. by later Tuesday, likely leading to an increase
in cloud cover.

Below normal temperatures are expected to persist early this
week, with highs in the 40s and lows in the 20s (coldest Tuesday
night, especially if we have less mid/high level cloud cover).

&&

.LONG TERM /WEDNESDAY THROUGH SUNDAY/...
High pressure will become centered overhead and shortwave ridging
will move in aloft for Wednesday, resulting in mostly sunny skies
and light winds. High temperatures on Wednesday will be in the low-
mid 40s.

A decaying shortwave will approach the area from the southwest late
Wednesday Night into Thursday. The GFS and Euro differ by a fair
amount with respect to the track of this feature. The GFS brings it
across the Central Mississippi Valley to near Detroit by Thursday
morning, while the Euro tracks the feature through the Ohio Valley
Wednesday Night and toward the Mason-Dixon Line Thursday morning.
The GFS solution would have minimal impacts on the area other than
producing clouds. The European solution would also produce cloud
cover, but with the disturbance closer by, it could also trigger a
few showers across western portions of the forecast area Wednesday
Night. Very few ensemble solutions produce any precipitation
Wednesday Night, so it appears that the Euro is a bit of an outlier
at this point, though temperatures will be cold if precip does
occur during this time.

A more substantial trough will eject from the Four Corners region
onto the Southern Plains during the day Thursday. This trough will
become meridionally elongated in nature Thursday Night, and
eventually cut itself off from the northern stream flow during the
day Friday as it tracks across the lower-mid Mississippi Valley.
Although there is some spread in the location of the trough amongst
model solutions, they are in good agreement that the trough will be
potent, with a well developed area of low pressure at the surface,
and a highly anomalous plume of moisture (GFS has precipitable water
values between +2 and +3 sigma) streaming northward ahead of the
system. The combination of strong forcing for ascent ahead of the
trough and the anomalously high moisture levels could lead to a
heavy rainfall event across the area Friday into Friday Night. The
operational GFS and Euro, as well as the ensemble means from the
GEFS and EPS all produce over an inch of precipitation with the
system.

With a strong area of high pressure departing off of New England at
the start of the event, some brief wintry precipitation can`t be
ruled out at precipitation`s onset late Thursday Night or early
Friday Morning, but it appears that most of the precipitation should
fall in the form of rain. Some wintry precipitation also can`t be
ruled out Saturday Morning on the back side of the system underneath
the upper low in upslope westerly flow. There is also a non-
zero chance the storm tries to spawn a secondary low along the
coast during this time.

&&

.AVIATION /02Z MONDAY THROUGH FRIDAY/...
VFR expected through Tuesday, except in central VA/INVOF CHO
where IFR continues this evening in snow. Improvement there
after 03z tonight is expected as well.

Light north flow is expected the next few days, generally 10 kts
or less.

Mainly VFR conditions are likely Wednesday and Thursday as a few
weak system cross. Condtions may deteriorate to sub-VFR by
Friday as the next system approaches.

&&

.MARINE...
SCA for middle/lower tidal Potomac and most of the MD portion of
the Chesapeake Bay south of the Bay Bridge tonight, scaling back
a touch before diminishing entirely by around midday Monday as
the gradient/northerly channeling weaken and high pressure
builds. Light winds are then expected through Tuesday.

Winds are expected to be light on Wednesday and Thursday with
surface high pressure located overhead.

&&

.CLIMATE...
Rainfall totals continue to creep upward, with Baltimore
setting the annual record already. Here are the current rankings
for wettest year on record (through December 5th):

Washington DC area (DCA)
1. 61.33 inches (1889)
2. 60.83 inches (2003)
3. 60.78 inches (2018)
4. 60.09 inches (1878)

Weather records for the Washington DC area have been kept at
what is now Ronald Reagan Washington National Airport (DCA)
since 1945. Precipitation records observed downtown extend the
period of record back to 1871.

Baltimore MD area (BWI)
1. 65.67 inches (2018)
2. 62.66 inches (2003)

Weather records for the Baltimore MD area have been kept at
what is now Baltimore-Washington International Thurgood Marshall
Airport (BWI) since 1950. Precipitation records observed
downtown extend the period of record back to 1871.

Dulles VA area (IAD)
1. 65.67 inches (2003)
2. 61.30 inches (2018)
3. 59.05 inches (1972)

Weather records have been kept at what is now Washington Dulles
International Airport (IAD) since 1960.

NOTE: All climate data are considered preliminary until
reviewed by the National Centers for Environmental Information
(NCEI).

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Winter Storm Warning until midnight EST tonight for MDZ017.
     Winter Weather Advisory until midnight EST tonight for MDZ016-
     018.
VA...Winter Storm Warning until midnight EST tonight for VAZ025-
     036>039-050-055>057-508.
     Winter Weather Advisory until midnight EST tonight for VAZ051-
     052-502.
WV...None.
MARINE...Small Craft Advisory until 6 AM EST Monday for ANZ536-540.
     Small Craft Advisory until 1 PM EST Monday for ANZ532>534-537-
     541>543.

&&

$$
SYNOPSIS...DHOF
NEAR TERM...MM/DHOF
SHORT TERM...DHOF
LONG TERM...KJP
AVIATION...MM/DHOF/KJP
MARINE...MM/DHOF/KJP
CLIMATE...WFO LWX