Scientific Forecaster Discussion
fxus61 kctp 110430
Area forecast discussion
National Weather Service State College PA
1130 PM EST Sat Dec 10 2016
high pressure will build south of the region overnight. Meanwhile
a new frontal system will approach for Sunday and Monday. It will
turn sharply colder behind a cold front on Tuesday, with a shot of
Arctic air and frigid temperatures expected through the end of the
Near term /until 6 am Sunday morning/...
some minor adjustments to the grids as of mid evening.
Clear across most of the area, but some high clouds just to the
west as of mid evening.
Snow is still well to the west. Did adjust wording some on the
statement, as any snow will be very light Sunday morning.
Most of the lake effect now north of our area. Abnormally warm
water of the Great Lakes is keeping activity going, as winds shift
more to the west and southwest.
Earlier discussion below.
Lows will drop back into the mid teens to lower 20s overnight.
Latest timing shows warm advection snows beginning over my western
zones before dawn on Sunday.
Short term /6 am Sunday morning through 6 PM Sunday/...
a Winter Weather Advisory has been issued.
Snow will overspread most of the region tomorrow morning. Precip
type Sunday will favor snow as the temps aloft will stay cold
enough during the day. Enough warm air may sneak into southwestern zones
to bring a wintry mix by late in the day, but the best chance of a
mix looks to hold off until Sunday night over southern zones. The
biggest question for southern PA tomorrow will be if they get
dry-slotted after the initial shot of warm advection scoots
through. This complicated the advisory decision a bit with the
main reasoning for headlines over southern areas being the
expected ice, which should hold off until late day or overnight.
But the quick burst of snow during the day will likely start
things off with deteriorating travel conditions so we decided to
keep the headlines simple.
Long term /Sunday night through Saturday/...
scattered snow showers Monday night across the western mtns of PA
will diminish as a weak ridge of high pressure at the sfc slides
east from the Ohio Valley. Tuesday will begin a cool down in temps
over a several day period as progressively cold chunks of Arctic
air move southeast ahead of the main, sub-500 dam polar vortex
that will be moving to near James Bay Canada by late Wednesday
The coldest airmass of this Young winter will spread into the region
for Thursday and Friday. Temps Thursday could conceivably struggle
to get above 10f for highs across the northwest mtns. The gefs shows a
small area of -2 to -3 sigma temps at 850 mb with values around
West-northwest wind gusting between 25 and 30 mph both Wednesday and
Thursday will create wind chills of 5-10 below zero during the
morning hours Thursday (mainly across the northwest mtns), and only in the
single digits during the daylight hours. Skies will become mainly
clear with the wind dying off Thursday night as a 1025 mb sfc high
build east from the nation's Heartland. This will set the stage
for frigid temperatures - but several degrees above record lows.
Min temps early Friday could dip to zero to 5 below across the
fresh snow covered ground of the Laurel Highlands and northwest mtns, and
will be in the single digits to teens.
Fair and dry (but very cold) weather is expected to persist Friday
night. However...a moisture-laden storm will likely impact a large
chunk of the region (beginning friday) with snow changing to mixed
precip of from the SW.
Saturday and Sunday, clouds will thicken up quickly and
precipitation will begin shortly afterward Saturday morning. It's
too early to give specifics on that storm W/resp that storm. 10/00z
ec and gefs do infer a widespread wintry (snow) precip
event...likely changing to some light sleet or fzra as the thicker
seeder/feeder cloud shield slides off to the east.
Aviation /06z Sunday through Thursday/...
southwest flow has pushed lake and orographic snows out of
central Pennsylvania. Mainly VFR conditions are across the region
at 04z, however, lowering cloud deck can already be seen advecting
in across central Ohio.
Widespread snow will overspread the region from west to east late
tonight into Sunday. Expect conditions to again lower to MVFR and
then quickly to IFR/LIFR over the western mountains as snow moves
in Sunday morning. Far southeastern terminals will likely remain south of
the precipitation and remain VFR before conditions lower later
The snow will mix with or change to sleet and freezing rain Sunday
night over the terminals south of about Interstate 80, before
tapering off as some light rain or snow showers Monday morning.
Mon...slowly improving conditions with precipitation tapering off
to rain or snow showers by Monday afternoon.
Tue-Wed...MVFR ceilings and light snow showers possible northwest. VFR
Thu...restrictions possible, mainly west and north with More Lake
effect snow showers. Gusty northwest wind.
Winter Weather Advisory from 4 am Sunday to 1 PM EST Monday