Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
550 PM EST Friday Feb 12 2016
an Arctic cold front will move through northwestern PA this
evening and across the susq valley shortly after midnight. This
front will be followed by the coldest air of the season and
strong/gusty northwest winds which will make dangerously cold wind
chills. Areas of significant lake effect and upslope snow are also
expected for the northwest mountains and Laurel Highlands during
the first part of the weekend. High pressure will settle across
the state late in the weekend...then a strengthening storm will
lift up the East Coast early next week.
Near term /until 6 am Saturday morning/...
530 PM update...
tweaks made to timing of shsn /slower by a few hours/ and mentioned
a coating poss in the southeastern half of the area this evening. Tailed
off the mentions of squalls as they would move through the area
based on latest snow squall parameters and loss of
lowering and thickening altostratus and Nova Scotia deck is now producing
steady light snow across the western half of Penn with visibilities
generally in the 1-3sm range as warm air advection. The light precipitation is the
result of weak warm air advection overspreading the area in advance of upper low
/polar vortex/ plunging south from James Bay.
Near term...high res models remain pretty consistent on the
timing of the Arctic frontal passage /across the far northwest in the 23-01z
window...and near the I-99/rt 22 corridor in SW and central Penn
between 03-05z...with the susq valley to be impacted by scattered
shsn/brief isolated squalls mainly after midnight.
The light warm advection snows late today and early tonight will
bring a general coating to one inch with some slick travel on area
The squalls later tonight will bring an additional coating to 2
inches of fluffy...wind whipped snow...though some localized 3
inch amounts aren/T out of the question where the initial NE/SW
band or two of squalls is followed-up by more boundary layer wind
parallel...narrow squalls later tonight/Sat morning.
Will highlight/track the timing of this squall band via special
weather statements as needed this evening and overnight.
We peppered the forecast area with a host of warnings and advisories
for snow/les...wind chills...and strong wind gusts Saturday. These
flags are staggered in time tonight...right through Sunday
morning. See phlwswctp and phlnpwctp /or our various social media
outlets - fb and twitter - for details.
Low temperatures at daybreak Sat will vary from slightly under zero
f across the northwest mountains...to the lower and middle teens in the susq
Short term /6 am Saturday morning through 6 PM Saturday/...
Arctic air mass will pour into the region early Saturday...accompanied
by gusty northwest winds...which will produce dangerous wind chills
across at least the northern and western mountains issued a Wind
Advisory outside of the previous wind chill flagged areas where
chills won't meet criteria...but winds will gusts around 40kt at
times throughout the day.
We'll see the coldest daytime temperatures since last winter
tomorrow. Gefs mean 800 mb temperatures between -22f and -25f should support
high temperatures Saturday only around zero across the northwest mountains...to the
lower and middle teens in the southeast.
Lake Huron connection should should focus the most persistent snow
showers across the northwest Warren Colorado and the Laurel Highlands...where
an additional inch or so seems likely based on ncar mesoscale
An additional few...to several inches of les and upslope snow likely
Sat across the northwest snowbelt and laurels...and advisories/warnings
for snow/les are in effect until 03z Sunday.
Elsewhere...dry Arctic air mass should preclude sig lake effect
snow across central PA Saturday.
Long term /Saturday night through Friday/...
*impact weather highlights: frigid temperatures and dangerous wind
chills for Valentines weekend. Potential winter storm early next
Polar vortex diving into northern New England will deliver the
coldest air of the season with Arctic blast into central PA
late Sat-sun. The global models and ensembles keep a mean trough
in place over the eastern US into the middle of next week
with several reinforcing shots of cold air moving through the mean
The most notable feature during the period will be a low pressure
system tracking up the East Coast on Tuesday. The latest model
guidance has trended west with the low track...but there is still
a decent spread. At this time precipitation with this system
appears likely Monday-Tuesday but the track will ultimately determine
precipitation type. Next week should end on a milder note.
The coldest temperatures/wchills expected Sat night over the area...as
800 mb temperature anomalies of near 3sd blw climatology graze the area. Minimum
temperatures Saturday night into early Sunday morning expected to
range from around zero in the lower susq valley to -10f in the
northwest mountains the frigid temperatures combined with dangerous
wind chills /-10 to -25 below zero/ will result in an increased
risk for frostbite and hypothermia.
The model spread has narrowed a bit concerning a potential winter
storm system impacting the middle Atlantic/northeast next Mon-Tue. Latest
gefs and ecens indicating a surface low track across eastern PA is
most likely...which would favor rain across all but perhaps the West
Mountains confidence remains low on ptypes across western PA...but now
definitely favors rain across the east. All the models are
signaling a significant quantitative precipitation forecast event...and therefore have increased
probability of precipitation in the likely range for Monday night through Tuesday.
A moderating trend is expected later next week...as heights are
forecast to rise and a possible low pressure system lifts through the
Great Lakes to the west of PA.
Aviation /00z Saturday through Wednesday/...
most of central PA will continue to be VFR into the middle
afternoon. West/SW winds will be 10 miles per hour or less much of the day.
Upper trough and weak warm advection light snow moves through the
region late this afternoon and evening...accompanied by 1-3sm
visibilities and MVFR to low end VFR ceilings spreading NE to cover the susq
valley by dark.
This synoptic light snow will be followed by a blast of Arctic
air. As Arctic air arrives /reaching northwest mountains by 00z/... more sig
snow showers/squalls will bring periods of LIFR/vlifr in this
evening into Saturday morning - especially over the northwest half of County Warning Area. These
will be accompanied by gusty northwesterly winds...and these brisk
winds will continue into Saturday.
Downslope flow kicks in late tonight...bringing improvement to VFR
in most places throughout the Central Ridge and valley region.
The western higher terrain will continue to see restrictions in
snow showers/blowing snow/upslope flow into the weekend.
Sat...windy. Shsn/reduced visible poss West Mountains...mainly am.
Sun...no sig weather expected.
Monday...PM snow possible.
Monday night and Tuesday...snow likely northwest half of Penn...with rain or
snow in the southeast.
wind chill warning from 4 am Saturday to 11 am EST Sunday for
Winter Weather Advisory until 10 PM EST Saturday for paz010-
Wind Chill Advisory from 4 am Saturday to 11 am EST Sunday for
Wind Advisory from 4 am to 5 PM EST Saturday for paz019-
Wind Chill Advisory from 5 PM Saturday to 11 am EST Sunday for
Lake effect Snow Advisory until 10 PM EST Saturday for paz005.
Lake effect snow warning until 10 PM EST Saturday for paz004.