Area Forecast Discussion
Issued by NWS Sterling, VA

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FXUS61 KLWX 110301
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
1001 PM EST Wed Jan 10 2018

.SYNOPSIS...
High pressure will continue shifting eastward into the Atlantic
tonight into Thursday. A broad area of low pressure will
approach the area late Thursday into Friday, with a cold front
expected to pass through the region Saturday morning. High
pressure of Canadian origin builds across the region through
early next week.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
The center of the surface high has shifted offshore of the
northeastern US, but an elongated ridge axis remains entrenched
over the region and will remain in place through tonight and
into Thursday morning. This will provide for mainly dry weather
and light winds.

Stratus deck continues to hold firmly in place this afternoon
from central and eastern Maryland southwestward into central
Virginia. A relatively small area remains clear in eastern West
Virginia, western Maryland and northwestern Virginia. These
areas have radiated, but elsewhere, clouds are keeping temps
fairly steady.

An expansion of the stratus deck is likely overnight,
especially towards morning as warm air advection continues aloft
atop a cooler wedge of air near the surface. Some very light
rain or drizzle is also possible towards morning in the southern
Shenandoah Valley, along the Blue Ridge, and into Highland
County. In addition, model guidance is insistent on bringing in
fog to portions of the region, and while widespread dense fog is
currently not expected due to the forecast stratus, areas of
light fog/mist are certainly possible with the strong low level
inversion. Lows tonight will be generally in the 30s.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
The surface ridging will shift further east away from the
region during the day Thursday giving way to southerly flow and
increasing moisture ahead of a system digging through the
central/southern Plains states. Expecting an overcast day across
the region with some morning fog and possibly areas of light
rain/drizzle southwest giving way to increasing chances of more
steady rain starting during the early to mid afternoon across
central/western VA and spreading northeastward towards the metro
areas towards and evening. This rain will then overspread the
entire region Thursday night. A rumble of thunder is also
possible, but coverage/confidence too low for inclusion at this
time. Highs should reach the upper 40s to low 50s on Thursday
and likely remain steady or rise Thursday night.

The first wave of rain will taper off Friday morning, giving
way to a break in the precipitation Friday afternoon. This
combined with increasing southerly flow should allow for
temperatures to reach the 60s for most locations.

The low pressure system will move northeastward near the
Appalachians Friday/Friday night and into southern New England
by Saturday morning. This will drag a cold front across the
region Friday night and early Saturday morning. An additional
period of rain is expected, along with the potential for another
rumble of thunder or even a convective fine line with some
gusty winds. As the front passes, rain may change over to some
wintry precip across the higher elevations of the West Virginia
and western Maryland, perhaps even northwestern Virginia, by
Saturday morning. Total areal-average liquid precipitation
amounts for the entirety of the storm from Thursday through
Saturday morning are currently projected in the 1-1.5" range.
While dry antecedent conditions should preclude any widespread
hydrological concerns, ice break up due to increasing warmth and
rain may create localized ice jam issues. Cold/partially frozen
ground reducing absorption may also lead to some ponding.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
A cold front will be over or just east of our CWA Saturday
morning. Some showers possible for part of the day as the front
moves away with upslope snow showers lingering maybe a little
longer. The upper level pattern behind this system will have an
upper trough over the eastern CONUS that will remain through at
least Tuesday.

The early cold front passage on Saturday will allow for the
high temperatures to be reached sometime between midnight and
dawn early Saturday. Temperatures will be falling through the
day due to strong cold air advection behind the front. High
pressure builds in on Saturday night and remains into Monday,
bringing dry and cooler conditions to our area. Temperatures
will be below normal but not as drastic as recent weeks. It
might feel pretty drastic, however, after the taste of spring on
Friday.

The upper level trough will be pushing east Monday night into
Wednesday. Guidance is in disagreement as to what -if any-
precipitation will approach the area Tuesday into Wednesday
either associated to a cold front or upper level disturbance.

&&

.AVIATION /03Z THURSDAY THROUGH MONDAY/...
VFR is generally expected for the remainder of the evening with
a stratus deck in place from roughly the Blue Ridge mountains
eastward. Ceilings are generally in the FL040-FL060 range and
should remain at or above these levels through at least
midnight. After midnight, stratus deck is likely to expand in
coverage and lower in height. Development of MVFR and
potentially IFR ceilings will be the main aviation concern late
tonight and into Thursday. Some light fog/mist is also
possible, especially at MTN/BWI. MRB is least at risk for any
fog or low ceilings.

Widespread rain is then expected to overspread CHO Thursday
afternoon, then the rest of the terminals Thursday evening and
last into Friday morning. This will bring IFR conditions in low
ceilings and visibilities. In addition, low level southerly
winds will be increasing and low level wind shear will become an
issue.

Some improvement in visibilities/ceilings are likely Friday
afternoon before another wave of rain moves in Friday night.

Sub-VFR conditions possible early on Saturday as cold front
crosses the region and then moves away. Conditions should
improve to VFR later on Saturday and remain VFR into Monday.

&&

.MARINE...
Sub-SCA winds are expected through at least Thursday with high
pressure overhead. Southerly flow will then increase Thursday
night, however mixing will be very limited as warmer air aloft
moves over the cooler waters. SCA will be possible Thursday
night, but for now kept below criteria as confidence not high
enough for issuance. SCA conditions may continue Friday and
Friday night.

Breezy conditions expected Saturday into part of the day on
Sunday that could reach SCA criteria. Winds should diminish
gradually through the day Sunday and remain below criteria into
Monday.

&&

.HYDROLOGY...
Warming conditions are expected through the end of the week,
along with periods of rain Thursday night through Friday night.
While dry antecedent conditions should preclude any widespread
hydrological concerns, ice break up due to increasing warmth and
rain may create localized ice jam issues. Confidence is
currently too low and threat too isolated to include in the HWO
at the moment, but we will continue to monitor. Around one to
one and a half inches of rainfall is anticipated during this
period, subject to change based on finer scale details yet to be
ironed out.

&&

.CLIMATE...
The recent brutal cold stretch has finally snapped. The cold
peaked during the first week of January, making it one of the
coldest on record for our area (and much of the eastern United
States). Below is a list of record coldest first weeks of
January (1st through 7th).

Washington DC area (DCA)
1. 16.8 degrees (1918)
   16.8 degrees (1879)
3. 18.4 degrees (1877)
4. 19.0 degrees (2018)
5. 21.1 degrees (1877)
Temperature records date back to 1872

Baltimore MD area (BWI)
1. 15.2 degrees (2018)
2. 18.4 degrees (1918)
Temperature records date back to 1872

Dulles VA area (IAD)
1. 15.3 degrees (2018)
2. 19.5 degrees (1968)
Temperature records date back to 1960

Meteorological winter (which began December 1st) has also been
very dry so far. Below is a list of the top 5 driest
meteorological winters (December 1st through February 28th/29th)
on record.

Washington DC area (DCA)
1. 2.60 inches (1871-72)
2. 3.32 inches (2001-02)
3. 3.85 inches (1980-81)
4. 4.15 inches (1976-77)
5. 4.76 inches (1873-74)

Notes: The winter of 1870-71 had 4.16 inches, but 31 days of
data are missing (no data for December 1870). So far, Winter
2017-18 has had 0.66 inches through January 8th. Precipitation
records date back to 1871.

Baltimore MD area (BWI)
1. 4.03 inches (1976-77)
2. 4.12 inches (1980-81)
3. 4.28 inches (2001-02)
4. 4.30 inches (1871-72)
5. 4.51 inches (1979-80)

Notes: The winter of 1870-71 had 2.93 inches, but 31 days of
data are missing (no data for December 1870). So far, Winter
2017-18 has had 1.07 inches through January 8th. Precipitation
records date back to 1871.

Dulles VA area (IAD)
1. 3.24 inches (2001-02)
2. 3.37 inches (1976-77)
3. 4.83 inches (1979-80)
4. 5.18 inches (1980-81)
5. 5.55 inches (2010-11)

Notes: The winter of 1962-63 had 0.00 inches, but 38 days of
data are missing. The winter of 1961-62 had 5.34 inches, but 34
days of data are missing. So far, Winter 2017-18 has had 0.80
inches through January 8th. Precipitation records date back to
1960.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...None.
VA...None.
WV...None.
MARINE...None.

&&

$$
SYNOPSIS...MM/RCM
NEAR TERM...MM/RCM
SHORT TERM...MM/RCM
LONG TERM...IMR/RCM
AVIATION...MM/IMR/RCM
MARINE...MM/IMR/RCM
HYDROLOGY...MM
CLIMATE...DHOF



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