Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1022 PM EST Thursday Nov 27 2014
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
Near term /until 6 am Friday morning/...
did up probability of precipitation and snow amts some for McKean...Cambria...and
Somerset counties. Had chance probability of precipitation...went up to likely in some
spots...with a few inches.
First concern is clusters of snow showers...which are largely
convective...given cold air aloft. No real focus...more concern
about rate of fall...than amts...see severe weather potential statement.
Second concern is lake response. As wind fields become more
west to northwest...input from the upper lakes may be more of a factor
late tonight. Starting to see radar returns at rather far
distance for snow...just SW of buf.
At this point still do not expect significant snow accums with
both these...but there could be enough to coat roads and cause
some slick spots...so have updated phlhwoctp to give the
public/customers a heads up.
Will continue to monitor the situation and update as needed.
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 European model (ecmwf) 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
Aviation /03z Friday through Tuesday/...
28/03z update...minor changes overall for the 03z intermediate
update. Regional radar is showing a fairly organized band of shsn
taking aim on the Laurel Highlands /jst terminal/ and therefore
dropped prevailing visible to 1sm. Visbys blw 1sm are likely at times
and may need to consider tempo for this condition.
28/00z...an upper level trough will cross the region tonight and
early Friday...driving a new surge of cold air over the relatively
warm lakes. A sufficient northwesterly fetch will be in place for
numerous snow showers mainly over the western 1/3 of the airspace -
with IFR impacts felt primarily at the higher elevation terminals
in zob sector. Periods of IFR are a good bet at jst/bfd with
greater confidence at jst. Downslope to the east should keep MVFR
to VFR conds in place through Friday. The shsn activity should taper
down over the western sections by later Friday afternoon with improving
conds expected at bfd and jst.
Friday...IFR-MVFR/-shsn west...improving. MVFR to VFR elsewhere.
Sat...VFR/MVFR. Isolated -shrasn possible.
Sun...MVFR/IFR. Occasional -shra northwest 1/2.
Monday...MVFR with occasional IFR. Scattered -shra. Cold frontal passage/wind shift 250-300.
Tuesday...VFR/MVFR ceilings. No sig weather.
short term...la corte