Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1230 PM EST sun Feb 7 2016
high pressure will provide one more fair and relatively mild
day today. A 36 to 48 hour period of snow will likely result in a
a widespread light to moderate snowfall for much of central PA
Monday night through Tuesday. Lake effect and upslope snow showers
will continue through the end of the week with additional
accumulation likely in the favored northwest snowbelt and higher
terrain along the alleghenies and laurels. A much colder weather
pattern is expected by later in the week with a blast of Arctic
air for Valentines weekend.
Near term /through tonight/...
skies are almost perfectly clear across the forecast area as we
remain sandwiched between clouds to the north and south.
Fair and mild conditions will continue today squeezing in one
last day before a slowly developing upper low drops into the
eastern US and brings a prolonged period of inclement weather to
the region for the new work week.
For the overnight we will begin to see a slow increase in
cloudiness. It will still be relatively mild with lows in the 20s
in most areas.
Short term /Monday through Tuesday night/...
considerable uncertainty exists with the onset of what at least
initially looks like some light precipitation as the upper low
digs through the upper Midwest on a track toward the Ohio Valley
and eventually northestern US.
The sref was slowest in bringing in the precipitation Monday...which
could actually be a light mix of rain and snow given the expected
highs in the 30s to lower 40s. I used our blended model probability of precipitation which
are a bit higher than the dry sref for the afternoon...with the
best chance of some light snow...or a light rain/snow mixture
being over western areas...with lesser chances over eastern zones.
In general I cut the already light wpc-guidance snowfall amounts
by about half given that skin temperatures will be relatively warm and
with precipitation rates which are expected to be on the light side.
That usually makes it hard for snow to stick to much more than
grassy surfaces...even in areas where it does not mix with rain.
It is fairly certain central PA will experience a prolonged period
of light...possibly moderate precipitation for the early part of the
extended period of the forecast. Confidence remains low however
as to which period will see the best chance of snow amounts that
might warrant headlines. The gefs shows at best a 30% probability of half
inch quantitative precipitation forecast in the period between 06z and 18z Tuesday. The ecens is
similarly Low Key regarding the best period for accumulate
snow...taking 6 days to reach 6 inch totals...and those are in the
usual lake effect and Laurel Highland upslope areas...not
necessarily associated with a single coherent surface cyclone.
The 00z GFS comes the closest to zeroing in on a threat
area...showing the southeastern 1/3 of the County Warning Area under the gun after 06z
Tuesday through 18z...with an elongated surface low helping
support an area of frontogenetic forcing into the lower susq
valley. It supports this idea with about 12-18 hours of fairly
strong easterly low level flow which the gefs is not nearly as
robust in portraying. The ecens for the same time frame has a
much less virile depiction of this wrap-back into the southeastern areas.
The NAM/sref are similarly less impressive with the potential for
sig snow over southeastern zones. It all points to continuing low
confidence in picking out the best periods for the most quantitative precipitation forecast...but
a relatively high confidence that once precipitation begins...it will
continue for several forecast periods.
Long term /Wednesday through Saturday/...
anomalous western US ridge/eastern US trough pattern will be in
place through middle week. The global ensemble means generally keep
this pattern configuration intact into the weekend but at a
slightly decreasing amplitude..especially the western US ridge.
As the broad upper level circulation departs over the northeast
toward the end of the week...the global models show it being
replaced by a polar vortex dropping south from the Arctic. Cold
air will begin spilling southward from Canada later in the week
reinforced initially by a secondary front on Thursday...followed
by a significant Arctic air intrusion for valentine's weekend.
Residual snows associated with the upper trough on Wednesday should
transition toward lake effect/upslope for several days Thursday-Sat
with additional accumulation likely over the favored areas downwind
of Lake Erie and in the higher terrain of the alleghenies/laurels.
Confidence is high in the forecast cold pattern which should peak
over the weekend. Maximum/min temperature departures of 20 degrees
below climatology are probable Sat-sun. Widespread sub zero wind chills
appear likely Saturday night into early Sunday...with projected
minimum wc values between -10 to -25 degrees below zero.
Aviation /18z Sunday through Friday/...
12z tafs sent.
Some fog at lns at times...but overall looking at VFR conditions
High pressure over the area will result in just a few high clouds
late today. Nice day for early Feb.
A complex weather pattern may result in some snow and colder
temperatures after today.
Monday...PM light snow possible...especially West Mountains
Tuesday...light snow possible...especially West Mountains
Wednesday...IFR/MVFR in shsn western airspace. MVFR-VFR ceilings central/east.
Surface wind gusts 20+kt from 270-300.
Thursday...MVFR in -shsn possible West Mountains
near term...la corte
short term...la corte