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000 
FXUS61 KLWX 130850
AFDLWX

Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
350 AM EST Wed Dec 13 2017

.SYNOPSIS...
Weak high pressure will build overhead today. An Alberta 
Clipper will pass nearby tonight through early Thursday. 
Developing low pressure will pass off the east coast late Friday 
and high pressure will return for Saturday. Low pressure may 
impact the area early next week.

&&

.NEAR TERM /THROUGH TODAY/...
Strong northwest flow continues this morning on the backside of
the departing low pressure system along the coast of Maine. 
Gusts up to 25-35 mph will likely continue through the first 
half of the day before abating during the afternoon hours as 
weak ridging builds in. Lingering upslope snow showers along the
Allegheny Front early this morning will diminish as the morning
wears on. Clouds streaming into the region in the northwest 
flow will also lessen in coverage, with most locations becoming 
mostly sunny for a period later this morning and into the early 
afternoon before clouds increase again ahead of the next fast 
moving clipper system.

Temperatures will be around 10 degrees or so below climatological 
normals for the day with highs only reaching the 30s. With morning 
temperatures in the single digits and teens in the higher 
elevations, combined with the gusty northwest winds, Wind Chill 
Advisories remain in place through Noon for wind chills near
-10F.

&&

.SHORT TERM /TONIGHT THROUGH FRIDAY NIGHT/...
Fast-moving clipper low diving through the Midwest today will
track eastward tonight, moving along or just north of the 
Mason Dixon line, and be off of the NJ coastline by sunrise 
Thursday.

Warm air advection will begin late today and this evening, and
some light snow will spread into parts of West Virginia and 
western Maryland during the late day and evening hours, and 
spread eastward during the first half of the night. With the 
warm front expected to set up just north of the PA/MD border, 
much of the precipitation should remain across PA, but some 
light snow is possible as far south as the metros during the 
late evening and first half of tonight. As the surface low 
tracks eastward, the surface cold front will move across the 
region from west to east, bringing a return to 
west/northwesterly flow by Thursday morning. Another period of 
upslope snow is likely along and west of the Allegheny Front 
between midnight and sunrise Thursday. Forecast NAM12 Froude 
numbers indicate relatively terrain-blocked low level flow until
Thursday morning, which would focus much of the precip west of 
the Allegheny Front. With the combination of light snow from the
warm air advection as well as the upslope, have issued Winter 
Weather Advisories for 2-4" of snow for the western portions of 
Grant, Mineral, and Allegheny Counties.

The low will pull rapidly away during the day Thursday, with
upslope snow showers diminishing. Gusty northwest winds to 25 
mph or so are expected, with highs in the 30s/40s. High pressure
will build in for Thursday night.

Another fast-moving shortwave trough will move towards the
region Friday, with a surface low tracking through the Great 
Lakes, and a secondary low developing offshore. This will bring 
the chance of a few additional snow showers. Temperatures remain
cold, with highs in the 30s to around 40F for Friday. Lows 
mainly in the 20s.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
High pressure will build overhead Saturday through Saturday
night...bringing dry and seasonably chilly conditions. The high
will move offshore Sunday and a southerly flow will allow for
milder conditions compared to recent days. However...low
pressure and its associated cold front will approach later
Sunday before passing through Sunday night into Monday. Showers
are possible ahead of this system later Sunday into Monday. 

Another upper-level disturbance may impact the area later Monday
or Tuesday...but confidence is low at this time. Seasonable
temperatures are most likely during this time. 

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
Primarily VFR is expected for the region through Friday night.
Gusty northwest winds up to around 30 knots will continue 
through the first half of today, gradually relaxing this 
afternoon. Some areas of light snow are possible this evening 
and tonight and brief reductions are possible, with MRB/BWI/MTN 
having the highest probabilities of seeing snow. Afterward, dry 
conditions expected Thursday and Thursday night, with another 
chance of some snow showers on Friday.

VFR conditions are expected for Saturday through midday Sunday.
A few showers are possible later Sunday into Sunday night.
SubVFR conditions are possible during this time. 

&&

.MARINE...
Gale Warning continues for all waters until 6 AM this morning
for gusty northwest winds, dropping off to the lower Tidal 
Potomac and Chesapeake Bay for the rest of the day, with SCA 
continuing for remaining waters. Winds will turn southerly 
tonight, with SCA in place over the lower Tidal Potomac and 
Chesapeake Bay. As a low pressure system crosses late tonight, 
gusty northwest winds return on Thursday, and SCA is in effect 
for all waters.

Winds will relax Thursday night into Friday with sub-SCA
conditions forecast, but SCA winds possible again Friday night
behind another low pressure system.

High pressure will approach Saturday before building overhead
Saturday night. A Small Craft Advisory may be needed for
portions of the waters Saturday. 

Low pressure and its associated cold front may impact the waters
later Sunday and Sunday night. 

&&

.TIDES/COASTAL FLOODING...
Strong northwest winds have caused tidal anomalies to drop
sharply. Blowout conditions are likely through the low tide this
morning...especially across the middle portion of the Chesapeake
Bay. Anomalies will increase later this afternoon through
tonight as winds turn to the southwest. 

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...None.
MD...Wind Chill Advisory until noon EST today for MDZ501.
     Winter Weather Advisory from 7 PM this evening to 7 AM EST 
     Thursday for MDZ501.
VA...Wind Chill Advisory until noon EST today for VAZ503-504-507-
     508.
WV...Wind Chill Advisory until noon EST today for WVZ501-503-505-
     506.
     Winter Weather Advisory from 7 PM this evening to 7 AM EST 
     Thursday for WVZ501-503.
MARINE...Small Craft Advisory from 6 PM this evening to 6 PM EST 
     Thursday for ANZ530>534-537-539>541-543.
     Gale Warning until 6 PM EST this evening for ANZ530>534-537-
     539>541-543.
     Small Craft Advisory from 6 AM this morning to 6 PM EST this 
     evening for ANZ535-536-538-542.
     Small Craft Advisory from 8 AM to 6 PM EST Thursday for ANZ535-
     536-538-542.
     Gale Warning until 6 AM EST early this morning for ANZ535-536-
     538-542.

&&

$$
SYNOPSIS...BJL
NEAR TERM...MM
SHORT TERM...MM

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