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Area forecast discussion 
National Weather Service State College PA
340 PM EST Thursday Nov 27 2014

Synopsis...
a weak upper air disturbance will keep clouds and the chance of a
few light snow showers in the forecast tonight and Friday.
Temperatures will begin to moderate this weekend as high pressure
moves off the southeast coast. The next disturbance will bring light
rain showers early next week before a quick shot of cooler air for
midweek.

&&

Near term /until 6 am Friday morning/...
latest surface analysis shows a weak surface low near cape Hatters and
along the West Coast of Lake Ontario...supported by several
shortwaves swinging east from the Tennessee Valley. This energy
and resulting surface convergence/upslope flow is forcing an area of
light snow across the northern and central mountains that will affect parts
of central PA into the evening hours into the central counties.

At this point still do not expect significant snow accums with
but could be enough to coat roads and cause some slipper
spots...so have updated phlhwoctp to give the public/customers a
heads up.

Biggest question for the overnight will be whether a period of
more organized lake effect can gather itself over northwestern areas. Deep
layer flow does look favorable for a time tonight...but relatively
short over-lake trajectories should limit snowfall to mainly sub
advisory levels.

&&

Short term /6 am Friday morning through 6 PM Friday/...
inversion heights are expected to lower Friday which should put a
damper on any of the best developed lake effect bands...but clouds
and perhaps a few snow showers will remain possible over the
normal western and northern locations. The best chances will be
in the morning...with brightening skies likely in the afternoon.

Highs will be a few degree cooler than today as the core of the Post
frontal cold air settles overhead.

&&

Long term /Friday night through Thursday/...
broad zonal flow develops during the weekend. This will prompt a
warm-up as low level flow veers to the SW as high pressure slips
off further to our southeast.

After a chilly night Friday night with lows in vicinity of 20f...the airmass
will begin moderating on Saturday...with readings reaching the
middle 40s to middle 50s by Sunday. May see scattered light shsn across northwest
mountains in weak northwest/west flow.

Models seem to be back in better agreement on approach of a front
for Monday...though GFS/gefs continue to be 6 to maybe 12 hours faster
with frontal passage.

Ahead of that...one area of possible concern could be the
expected development of some light warm advection precipitation Saturday
night into Sunday morning mainly across western sections. Temperatures
aloft warm rapidly...and I kept forecast surface mins mainly above
freezing. But if we end up a few degree cooler...we could see a
period of some light icing until temperatures can recover Sunday.

Post front will bring cooler temperatures back in for midweek as large
surface high slides across S Canada...but notable model diffs
begin to develop around then with ecmfw much flatter than GFS. Ec
solution brings high pressure over the region by late week with
slowly moderating temperatures...while the GFS/gefs spins up a surface
low over the Midwest which would push even warmer temperatures our way.
For now...tempered warmup a bit as much uncertainty in later time
periods.

&&

Aviation /20z Thursday through Tuesday/...
latest surface analysis shows a weak surface low near Cape Hatteras and
along the West Coast of Lake Ontario...supported by several
shortwaves swinging east from the Tennessee Valley. This energy
and resulting surface convergence/upslope flow is forcing an area of
light snow across the northern and central mountains that will affect parts
of central PA into the evening hours into the central counties. As
support moves east of the mountains...expect downsloping to limit
coverage of the snow.

The light snow will lead to MVFR visibilities and IFR ceilings at western and
central airfields. A few periods of IFR ceilings are also possible.

Elsewhere...the few degree c inversion between 4-5 kft above ground level...and the
relatively light northwest beneath this stable layer...will make for a
rather hazy/stagnant late morning to early afternoon.

The northwest breeze will pick up a bit after 15z...helping to mix out
and erode the lower stratus bases across much of the alleghenies.
However...moist upslope flow /nearly orthoginal to the western PA
ridges/...and deepening of the cold air will lead to a gradual
increase in snow showers this afternoon and evening with periods
of IFR/LIFR likely at kbfd and kjst after 21z.

Later this afternoon expect plenty of strato cumulus /topped by a layer or
two of altocu and cirrus/ and relatively light northwest winds through
18-21z today with just some isolated to scattered snow showers
across the northwest mountains and Laurel Highlands /from kbfd to kjst/.

Some lake effect -shsn are forecast to develop late this afternoon
through tonight over the western 1/3 where reduced conds are likely to
persist. Coinciding with the snow showers...will be an increase in
the northwest winds and associated gusts.

Late day/night-time winds should gust in excess of 20kts across
the mountains of western Penn...while gusts elsewhere will likely be in
the middle to upper teens - mainly this afternoon and evening.

Outlook...

Tonight...IFR/MVFR with occasional -shsn western 1/3. VFR to MVFR ceilings
cntrl/east.

Friday...am MVFR/-shsn northwest...otherwise becoming VFR.

Sat-sun...mainly VFR. Isolated -shra possible.

Monday...cold frontal passage. Mainly VFR. Scattered -shra possible.

&&

Ctp watches/warnings/advisories...
none.

&&

$$
Synopsis...la corte/gartner
near term...gartner
short term...la corte
long term...rxr
aviation...gartner

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