Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Pittsburgh PA
938 PM EST Wednesday Dec 11 2013
a cold front will bring another shot of Arctic air and snow
showers overnight. High pressure will end the snow showers
Thursday. Snow and a wintry mix will return for the weekend.
Near term /through Thursday/...
as of 9pm...cold front has crossed over most of the
region...except for the southeasternmost counties. Light snow is
mostly contained to the vicinity of the front...although some lake
effect snow showers remain to the north. The snow along the front
will continue to move to the east along with the front...providing
some very light snowfall accumulation. A heavier band of snow
formed along the Lake Erie shoreline in Ohio that has moved
inland...but the intensity of this band is decreasing as it
approaches our inland counties. Still think that another inch or
two of snow is possible to the north of Interstate 80 overnight
during the brief period that lake effect snow will be favorable.
Have made little change to temperatures or winds...and the ongoing
Wind Chill Advisory does not need any changes. Previous discussion
Arctic front working across Ohio this afternoon and will slide
through the region tonight. Little change to expected lake effect
as flow will become northwest for a window of lake effect overnight
with light accumulations mainly I-80. Elsewhere only a few snow
showers. The core of the cold air will arrive late tonight into
Thursday with 850mb temperatures approaching -20c. The surface high
associated with the cold air will be centered across the
Tennessee Valley Thursday morning allowing a pressure gradient to
remain fairly tight across the region through Thursday. With winds
at 10 to 15 miles per hour overnight and single digit temperatures into
Thursday morning wind chills across the higher elevations will
drop below -10 degrees before daybreak toward noon. A Wind Chill
Advisory issued for all the ridge counties. Elsewhere wind chills
will drop below zero by daybreak and will issue an Special Weather Statement to
Flow will turn west during the day ending lake snow showers. With
the coldest air at 850 across region maximum temperatures will likely stay in
the teens Thursday.
Short term /Thursday night through Saturday night/...
core of cold air will begin to shift northeast Thursday night and
Friday as surface ridge moves to the East Coast. A frontal
boundary will be just north of the region and with upper flow
becoming zonal should have little effect on the region.
Temperatures will warm nearly 15 degrees Friday from Thursday but
still remain below normal.
Latest 12z models have come to a fairly close consensus on the
storm system for late Friday night into Saturday night. Warm
advection snow will quickly expand across the area before
daybreak Saturday. As surface low slides to near kmgw by Saturday
evening snow will be mixing with sleet/freezing rain toward the PA
Turnpike and in the ridges Saturday afternoon...with any mixed
precipitation changing to plain rain along I-70. By later Saturday night
coastal low will be developing and will steal best moisture and
dynamics and also bring cold advection back across region.
Looks to be a light quantitative precipitation forecast event with amounts around a quarter inch
or less liquid equivalent. The only exception will be for areas
north of the Turnpike and toward I-80 where precipitation will remain all
snow through the event and sustained warm advection could bring
Long term /Sunday through Wednesday/...
low pressure is prognosticated off the middle Atlantic coast sun...with lingering
snow shower chances across our region on the western side of the system. Lake effect
and upslope shsn are possible into Sun night but these should be ending by
Monday as high pressure builds in. Another cold front is prognosticated for Tuesday before
high pressure builds in again by Wednesday. Below average temperatures are expd to continue through
Aviation /03z Thursday through Monday/...
snow showers along passing cold front tonight will bring MVFR
conditions with brief IFR for terminals around kpit and north.
Winds will gust up to 20kt briefly from the west-northwest as the front
passes. Behind the front...expect MVFR stratocu ceilings to linger
through middle morning. Conditions will gradually improve to VFR by
early afternoon with a broken middle deck except for kfkl and kduj
where low end VFR stratocu ceilings will likely remain.
Outlook.../Thursday night through Monday/...
VFR conds under high pressure expd through Friday evening before a low pressure system
brings rstrns overnight Friday through Erly sun.
Maryland...Wind Chill Advisory from 4 am to 1 PM EST Thursday for mdz001.
PA...Wind Chill Advisory from 4 am to 1 PM EST Thursday for paz074-
WV...Wind Chill Advisory from 4 am to 1 PM EST Thursday for wvz023-