Area Forecast Discussion
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000
FXUS61 KPBZ 120223
AFDPBZ

Area Forecast Discussion
National Weather Service Pittsburgh PA
923 PM EST Mon Dec 11 2017

.SYNOPSIS...
Much colder weather arrives Tuesday along with snow. Heavy lake
effect snow showers will be possible through mid- week. Another
system early Thursday could bring a light accumulation. A brief
warm up this weekend.

&&

.NEAR TERM /THROUGH TUESDAY/...
Latest analysis shows surface low centered over Indiana which is
progged by latest short term guidance to begin crossing the top
half of the forecast area shortly after midnight. Precipitation
will be primarily north of I-70. Still expecting precip type to
be snow as drier air aloft should be sufficient to wetbulb
temperatures down quickly once precipitation starts in any
locations above freezing. Any accumulation prior to daybreak
will be less than an inch south of I-80...1-2" north of I-80.

Temperatures will dropping throughout the day along with strong
winds will result in wind chill values from the teens to single
digits by the afternoon.

&&

.SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/...
Snow Amounts:
Forecast still on track for the first significant lake event of
the season. Eq levels extend up to 11KFT while steep low level
lapse rates intersect a favorable thermal profile within the
dendritic growth zone. Given flow off the lake, high resolution
CAM models agree with recent events of a snow band extending
into northern parts of Venango and Clarion counties Tuesday
night then retreating into Forest county Wednesday morning. This
is where highest snowfall totals are predicted. Counties to the
east and west have been placed under a winter weather advisory
given boundary flow not being favorable for heavy lake effect.
If the wind changes by 20 degrees then we will need to revisit
current advisories.

The double fetch will allow bands to extend all the way into the
Laurel mountains where winter weather advisories were issued.
Higher snowfall totals are expected in southwest PA than the
mountains of northern WV and western MD due to flow and moisture
depth. Most of the snow that accumulates in the mountains of
Garrett, Tucker, and Preston will occur Tuesday during the day
with the front. There could be near zero visibility with squalls
in the this region during the 15z-18z time frame along the
baroclinic zone.

Snowfall amounts where adjusted a little lower for tonight,
otherwise little if any changes through Wednesday.

Winds:
As low pressure deepens off to our east winds will pick Tuesday
night into Wednesday. Mixing heights support gusts close to 40
mph. Can not rule out higher speeds on the ridge tops during the
early morning hours Wednesday. Elsewhere in the lower
elevations speeds will stay at most in the lower to mid 30s.

Wind Chills:
Arctic air and northwest winds will bring sub zero wind chills
over a good chunk of the region Tuesday evening through
Wednesday morning. Lowest values will be in the mountains as
they fall between -10 to -15 degrees. This has prompted a wind
chill advisory which was bundled up within the winter weather
advisory /criteria -10 to -24F/ for Preston, Tucker, and
Garrett counties.

Next System:
12Z NCEP suite still portrays a weak low pressure system
tracking south of Interstate 70 Wednesday night into Thursday
morning. What warm advection exists on the front of the system
won`t be enough to keep ptype anything other than snow. If this
track holds locations that don`t receive much in the way of
snowfall /eastern Ohio, northern WV outside the mountains, and
southwest Pennsylvania/ could see a quick coating of 1-2 inches
around the morning rush hour. This has been highlighted in the
hazardous weather outlook given impact level and first snow of
the season for aforementioned locations. In the higher terrain,
snow amounts may be high enough to warrant a winter weather
advisory.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Highlights:
- Snow showers lingering Friday
- Temps creeping back to normal
- Next weather system Sunday

Mid level trough sweeps through Friday, however with westerly
flow and it not being that strong, do not expect much additional
snow accumulation. The mountains of western Maryland and
northern West Virginia could see a light accumulation during the
day given position of dendritic layer and moisture depth
extending around 10KFT.

H5 heights build as transitory ridge crosses the region. A
short break in the active weather pattern Saturday. With a
little sunshine despite increase mid and upper level clouds. Temperatures
should climb into the 40s for the first time in several days
save for locations which will have snow cover as they remain in
the 30s. Low pressure crosses through the western Great Lakes
spreading moisture from the southwest. Thermal profiles and
projected onset time have ptype not being an issue at thus
juncture. If precip starts earlier there could be a wintry mix,
but plenty of time to resolve this as its six days down the
road.

&&

.AVIATION /02Z TUESDAY THROUGH SATURDAY/...
VFR conditions will deteriorate after midnight as snow showers
develop associated with crossing low pressure.

Kept similar timing for precip onset and restrictions - around
08-12z with greatest confidence in prolonged IFR at KFKL and
KDUJ but brief IFR visibility conditions possible elsewhere.

Expect some improvement later Tuesday outside of the terminals
impacted by lake-enhanced snow but general MVFR should prevail.

Southerly flow will continue until the passage of the front
overnight/tomorrow with a return to wnw flow with gusts to near
30kts.

.Outlook...
Periodic restrictions in snow showers and northwest flow will
continue through Wednesday. Another system will bring another
round of snow and restrictions to many of the terminals
Thursday.

&&

.PBZ WATCHES/WARNINGS/ADVISORIES...
MD...Winter Weather Advisory from 7 AM Tuesday to 7 AM EST
     Wednesday for MDZ001.
     Wind Chill Advisory from midnight Tuesday night to 7 AM EST
     Wednesday for MDZ001.
OH...None.
PA...Winter Weather Advisory from 7 AM Tuesday to 1 PM EST
     Wednesday for PAZ007-016.
     Lake Effect Snow Warning from 7 AM Tuesday to 1 PM EST
     Wednesday for PAZ008-009-015.
     Winter Weather Advisory from 7 AM Tuesday to 7 AM EST
     Wednesday for PAZ023-074-076.
WV...Winter Weather Advisory from 7 AM Tuesday to 7 AM EST
     Wednesday for WVZ510>514.
     Wind Chill Advisory from midnight Tuesday night to 7 AM EST
     Wednesday for WVZ512>514.

&&

$$



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