Scientific Forecaster Discussion
fxus61 kctp 112339
Area forecast discussion
National Weather Service State College PA
639 PM EST Wed Dec 11 2019
the leading edge of another shot of cold air will push in from
the northwest during the evening and early tonight accompanied
by a several hour period of clouds and some brief flurries. A
few heavier snow showers may occur near the New York border late
this afternoon and evening. A storm system will move up into
the state from the south on Friday. While a brief period of
mixed precipitation is possible on Friday, it will get milder
and it should turn to rain with moderately heavy amounts
between one half of an inch, and one inch.
Near term /until 6 am Thursday morning/...
added snow showers into points to the south and east of the
northwest areas. Radar and obs show narrow bands of snow bands
Earlier discussion below.
Positive tilted ridge of high pressure at the surface and
deep-layer subsidence beneath the left entrance region of a
departing/strong 190+ knots upper level jet was maintaining
a large area of generally clear skies and welcome sunshine
across the southeast two-thirds of the County Warning Area this mid afternoon hour.
Surface dewpoints are in the single digits to teens across the
region this midday hour, helping to create exceptional
An approaching jetlet and sfc cfrontal boundary will bring a
period of clouds and several hours of gusty westerly wind 30-35
mph later this afternoon and evening, but little more than a few
flurries are expected in most locations of central and northern
Latest href indicates that the current les band across the
greater buf area and its south towns will be pushed sewrd late
this afternoon and early evening by veering boundary layer
winds in the wake of the aforementioned front, but will begin to
quickly diminish in intensity by the time it reaches much of
the northern tier of PA around, or shortly dusk. Still, a few
brief snow showers near and north of Route 6 could reduce vsby
to 3/4sm or less between about 22z-01z.
Href indicates that there could be a light accumulation of up to
one inch of snow across far northern McKean and Warren counties
in the 11/22z to 12/01z period.
Temps for the next few hours will vary from the mid and upper
20s across the northwest mtns and Laurel Highlands, to the upper 30s
throughout the susq valley.
The center of a 1040mb high will drift over PA early Thursday,
which will support clear skies and mainly light wind. This will
yield min temps in the upper single digits in some spots up
north while teens to lower 20s will be common across the central
mtns and susq valley. Wind chills of 5 to 15 above will greet
people thurs am.
Short term /6 am Thursday morning through 6 PM Thursday/...
temps stay below normals on Thursday, with maxes u20s to m30s.
High pressure will slide off the mid Atlantic coast during the
day and supply plenty of sunshine and light wind in the morning.
The timing of mid and high cloud advection into the region after
such a cold morning across the northwest mtns could lead to a slight to
several deg f temp bust should they arrive earlier/thicker than
models indicate. In that case some downward adjustment will be
needed, mainly across the northwest half of the County Warning Area.
Long term /Thursday night through Wednesday/...
*freezing rain risk early Friday in the interior central ridges
*heavy rain possible (1-2 inches) in east-central PA Friday
night into Saturday
*period of snow/mixed precipitation likely later Monday into
tuesday; potential for winter weather should be monitored
High pressure retreats into the Canadian Maritimes Thursday
night into Friday morning. An amplifying trough over the lower
MS valley combined with broad southerly flow aloft will spread
precipitation northward into cpa on Friday. Timing/speed of the
precip remains critical for ptype delineation given warm
advection aloft and low level cold air entrenched near the
surface. Leaned on the fast-side with warming mins Thu night and
colder highs Fri as clouds and eventually precip spreads into
cpa. Web-bulb effects could be a factor for rain/snow/sleet
considerations but conceptual pattern seems to fit an ice to
rain transition mainly confined to the interior central ridges
before 00z Saturday. Overall impact appears to be limited with
sfc temps in the low 30s but will continue to mention in severe weather potential statement.
Low pressure system will draw deep moisture/above normal precipitable water
northward into the area Friday night resulting in widespread
moderate to heavy rainfall. Storm total rainfall of 1 to 2
inches is forecast across east-central PA. Will need to watch
for a transition back to snow on the backside of the system as
the upper low pivots into the northeast and gusty northwest
flow Ushers cold air back into the region. Lake effect snow
accumulation is likely in the favored upslope high terrain and
snowbelts Sat night into Sunday. Temperatures trend colder
Saturday to Monday as the active pattern briefly takes a pause.
Winter weather threat will need to be monitored for early next
week with the potential for snow and ice to impact the area
later Monday into Tuesday. Updated local winter storm outlook
graphics on the web and severe weather potential statement to reflect the latest trends/probs.
Below average temps are forecast into the second half of next
Aviation /00z Thursday through Monday/...
much of the County Warning Area will be VFR with just few-sct clouds in the
3.5-4.5 kft range.
Airfields across the western high terrain of PA will trend twd
cloudier conditions with VFR cloud bases initially through 21z,
then down into the lower end of VFR or solid MVFR range in the
meso-b scale area of weak warm air advection ahead of a secondary/Arctic-like
front during the late afternoon through early evening.
Intermittent IFR conditions poss in snow showers in the 22z-02z
period in vicinity of kbfd. Remainder of County Warning Area will remain VFR with a few
evening flurries central and west.
Westerly winds pick up further during the rest of afternoon,
with surface speeds of 10-20 mph some gusts to 25-35 mph, with
the strongest winds over the northwest half of the County Warning Area where some peak
gusts around 40 mph are possible.
Thu...no sig wx expected.
Fri...rain/low cigs likely, especially late.
Sat...rain/low cigs possible, especially early.
Sun...some rain and snow early, then clearing.
Mon-Tue...restrictions likely later Monday into Tuesday.