Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 010322
Area Forecast Discussion
National Weather Service State College PA
1022 PM EST Wed Nov 30 2016
A large upper trough and pool of colder air will move across the
region over the next 12 to 24 hours. The cold air and westerly
winds may trigger snow showers in northwestern Pennsylvania. A
series of troughs in the west will slowly build a ridge over the
eastern US early next week. It should warm up again ahead of
another 500 mb trough and cold front later next week.
.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
-- Changed Discussion --Large area of showers pushing out of my eastern counties associated
with strenghtening LLJ lifting over the northern Mid Atlantic
region...acting on soupy 1.25"+ PW air mass that covers the
eastern third to half of central PA. Sfc cold front with NCFRB
slowly pushing into the Alleghenies late this evening as per
regional radar mosaic. Sfc wnds g25-29kts with this feature across
Cold front which will move across the area overnight. Mild air
across central and eastern PA will be displaced quickly after
FROPA with temperatures falling through the 40s and into the 30s.
Rainfall will taper off to showers behind the front as well. Under
NW post frontal flow the showers will tend to favor the mountains
of the north and west.
-- End Changed Discussion --
.SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/...
Area under trough and NW flow Thursday. This will bring plenty of
cloud cover but limited snow shower activity mainly in the higher
elevations. Where it does snow, accumulations will be light and
mainly confined to higher elevations. Temperatures will be much
cooler and closer to seasonal average.
.LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/...
The cold air is in placed Thursday night and Friday. The 850 mb
temperatures are not impressive, in the -4 to -6 range. The colder
air and flow over the warm lakes should increase snow shower
activity in northwestern PA. Some guidance implies about -8C at
times. Most areas will be precipitation free Fri-Monday. Except
the northwestern areas where some LES is likely this weekend. The
more westerly flow is not as favorable for southwest mountains.
The GEFS/NAEFS/GFS have no QPF in southwest mountains. Focused
attention to minor LES snows in NW.
Late in the weekend and early next week the heights and 850 mb
temperature rise. Snow in NW should cut-off Saturday eve or early
Sunday. Then a slow and steady warm up is implied. High pressure
should be over us Sunday-Tuesday/Wednesday. Most areas will be
above 0C at 850 mb by Tuesday.
The issue in all the EFS is the potential cold air damming event
as the low moves into the Great Lakes. It may stay cooler in the
boundary layer Tue-Wed due to the surface high. The NAEFSBC and
GEFS imply this in the 2m temps and the 925 mb temps.
The always too wet GEFS biased our grids and has some warm
advection QPF by Monday. Any QPF would be very light. IF and only
IF there is precipitation there could be snow/rain-snow in
northern areas until overnight Monday into Tuesday. Rain farther
south and east. The GEFS and CMCE PWAT is close to normal with the
first two light QPF events. Not favorable for us to get rain.
Some more light QPF in the GEFS Tuesday so had chance rain showers
to slight chance again Tuesday. Not too confident in this still
weak pattern and low PWAT values
Our best chance for rain next week will likely be in the Thursday
timeframe when the cold front moves into the region. As forecast
it pulls about +1 sigma PWAT into our region. Thus, it may be the
best forcing mechanism. Thus the GEFS has the highest PDF based
POPS Wed into Thursday. We have over a week to deal with rain to
snow potential with that potential event.
.AVIATION /03Z THURSDAY THROUGH MONDAY/...
Over Susq Valley and eastern PA at 03z, a large area of rain with
embedded gusty showers (as 50+ kt 850mb jet lifts through bringing
LLWS) producing IFR conditions at KMDT-KLNS in high PW air mass.
The rain will continue to shift gradually eastward through this
evening as a warm front lifts through, with even a rumble or two
of thunder poss SE of KLNS, before conditions gradually improve to
VFR after 06z as westerly winds help to bring some drying to lower
levels through downsloping.
Cold front with NCFRB slowly pushing into western portions of cwa.
Gusty showers poss at KBFD-KJST through 04z, and along and north
of I-80 through 06z, but this feature will weaken over the central
and southern mtns as it pushes east. Conditions will be somewhat
variable ahead of the cold front (between the rain areas), but
overall will transition to less and less VFR and more widespread
MVFR/IFR. Post frontal WNW flow will bring long duration
widespread restrictions to the mountains of the north and west
starting tonight, and additionally a transition to snow showers
on Thu continuing into Sat.
Thu-Sat...Sct SHSN w/ocnl MVFR/IFR in BFD-JST.
Sun-Mon...Mainly VFR. Restrictions still poss NW.