Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 070435
Area Forecast Discussion
National Weather Service State College PA
1135 PM EST Tue Dec 6 2016
Low pressure over PA will fill and a coastal low will deepen and
move away on Wednesday. High pressure will briefly visit PA before
a dry but sharp cold front sweeps southeast across the area on
Thursday. A low pressure system is likely to track west of
Pennsylvania through the Great Lakes Sunday and Monday.
.NEAR TERM /UNTIL 9 AM WEDNESDAY MORNING/...
Whatever is left is going to be barely more than drizzle for the
rest of the night. Have jacked up mentions of fog as well with
very high ambient moisture and little wind (at this hour) over
most of the CWA. The wind over the W will continue to veer and
become westerly as the dry line/cold front moves across later
tonight and Wed AM. Will allow the advy to die at 11 PM.
Most places are above freezing now. Have begun the process of
cancelling flags by dropping the warning and part of the advy
since the precip is moving on through rapidly, now. Little more
than drizzle or very light snow will be left as the high clouds
move away and we lose the seeder-feeder process. There may still
be a pocket or two of FZDZ, but not widespread at all. Fog may
become dense - especially in areas with little wind and upslope
regions. Temps will likely stay within a few degs of 35F all
night. Early Wed morning, the temp profile will become more
favorable for flurries in the west before ending.
.SHORT TERM /9 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
Surface high pressure building into the region should supply a
dry Wednesday to Central PA. However, low level moisture trapped
beneath inversion and weak mixing will likely result in stubborn
low clouds across the NW Mtns. A downsloping westerly breeze and
some slightly drier air should result in partly to mostly sunny
skies east of the Mtns. Temperatures there should respond by
rising into the low-mid 40s, while cloud cover holds readings to
the mid 30s across the NW Mtns.
.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
The long term will begin with a brief period of tranquil
conditions and deep southwesterly flow, ahead of an arctic front
that will be pushing across the state Thursday morning and early
Clouds will thicken up Wednesday night and early Thursday with snow
showers moving into the far northwest around or shortly after
midnight, then spreading SE and possibly mixing with rain showers
across the Southeast half of the state Thursday morning.
The subsidence inversion base lifts rapidly up to, then well over
7-10 kft agl Thursday afternoon, right through Friday night as the
mean low to mid level flow becomes well-aligned from the
West-Northwest. The subsidence inversion base will drop gradually
down to below 7 kft agl during the day Saturday as the mean 925-700
mb flow backs to more of a west, then swrly direction by around
This scenario is very favorable for heavy, to locally excessive
Lake effect snow and significant amounts of blowing and drifting
snow with occasional wind gusts around 30 mph, and up to several
hundred j/kg of cape being transported SE of interstate 90 leading
to the potential of some Thundersnow with periods of 2+/hr snowfall
rates possible, especially Thursday night through Friday night as
quite anomalously cold air of -2 to -3 sigma in the 700-500 mb
layer moves overhead.
Posted a Winter Storm Watch for Warren and McKean counties from
Noon Thursday through 7 am Saturday, and the significant bands of
LES could even continue through much of the day Saturday. Snow
totals throughout the perennial snowbelt of NW Warren county
could top 18 inches by Saturday, with areas of 6-12 inches
further inland across the SE half of Warren county and at least
the NW half of McKean County.
Scattered narrow bands of snow showers will stream SE into the
Central Ridge and valley Region occasionally, with a coating to an
inch possible in a some locations.
Expect rather significant snow totals (in excess of 4 inches) to
also occur across the Laurel Highlands, albeit over a more
extended period Thursday night into Saturday, and with lighter
A bubble of high pressure at the sfc (and a weak ridge aloft)
will bring a brief period of tranquility (though very cold overnight
min temps) as it slides east across the forecast area late Saturday
into early Sunday. Expect partial clearing (and perhaps mostly
clear skies across the SE part of the CWA) for the middle third of
Deep, mean-layer flow backs to the southwest with a slug of low-mid
level warm advection sliding up and over the deep/retreating cold
airmass. This will create an area of steady light snow or snow
showers across mainly the northwest half of PA Sunday afternoon
and Sunday night.
The boundary layer could become warm enough by Monday to mix in
or changing the scattered light precipitation to rain showers,
throughout the Lower Susquehanna Valley.
One or more, weak and fast moving short waves in the zonal flow
aloft could bring some light mixed precipitation in the Ridge
and Valley Region, and scattered snow showers across the
.AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
-- Changed Discussion --Most of the precipitation is over as of 11 PM. 03Z TAFS sent.
Earlier discussion below.
A mixture of snow, sleet, rain, and freezing rain will continue
to taper off from west to east this evening, as the coastal
storm becomes the main storm. Expect a wide range of conditions
into Wednesday morning.
Expect most areas to become VFR by late morning on Wednesday, as
the storm moves away from the area.
Some snow showers will likely work into the north and west late
Thursday into early Saturday afternoon, as winds shift more to the
west and northwest off the Great Lakes.
A weak storm system tracking northeast across the Great Lakes on
Sunday may bring a few snow showers to the area late.
Thu-Fri...Becoming windy with periods of snow showers, mainly late
Thursday into Friday. Mainly MVFR/IFR west to MVFR/VFR east.
Sat...Decreasing winds. Low cigs/-SHSN psbl NW. VFR east.
Sun...Some snow possible. Mainly late across the NW.
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Temp/dewpoint sensor at KIPT appears to be malfunctioning. Far too
warm compared to meso obs and surrounding METARs. Have used a
more-representative 40F for the max for today at KIPT. Techs have
been advised and repair is estimated to be done on Wed.
-- Changed Discussion --Lake Effect Snow Watch from Thursday afternoon through
Saturday morning for PAZ004-005.
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