511 
fxus61 kctp 030003 
afdctp 


Area forecast discussion 
National Weather Service State College PA 
703 PM EST Tuesday Dec 2 2008 


Synopsis... 
a weakening upper level trough sliding across the northeast will 
continue to weaken tonight. A ridge of high pressure will build 
along the East Coast Wednesday...followed by a strong cold front 
on Thursday. Additional unsettled weather is possible this 
weekend. 


&& 


Near term /through Wednesday/... 
a period of quieter weather is in store for tonight as surface 
high builds in from the south. Stratocu will linger for several 
more hours as inversion lowers...but should begin to noticeably 
dissipate this evening. Temperatures will drop off below guidance in snow 
covered areas...and finish near or slightly above guidance 
elsewhere. A brief period of milder weather is in store for 
Wednesday...eventually yielding to increasing clouds/moisture ahead of 
an approaching Great Lakes/MS valley frontal system late in the day. 


&& 


Short term /Wednesday night through Friday night/... 
xpect increasing clouds early Wednesday night...as strong cloud fnt approaches 
from the Great Lakes/Ohio Valley. Min temperature forecast is somewhat problematic given 
low level warm advection...clouds...and increase southwesterly flow ahead of the fnt. Feel 
that the overall diurnal range will be limited...and thus have 
hedged lows a few degrees above guidance. For probability of precipitation followed close to the sref 
for timing and coverage...ramping up from schc to likely in the west 
by 12z Thursday. Blyr temperatures look marginal for all snow at the onset of 
frontal precipitation...so have continued a rain or snow ptype. Sref plumes also 
show the ptype uncertainty...with several rain and snow members 
prior to 15-18z in the west/central zones. 


The potent/Arctic cold front will be accompanied by a sharp low level 
thermal gradient as it moves across central Penn on Thursday. Strong 
cold air advection will quickly overspread the region immediately in 
the wake of the frontal passage...resulting in falling temperatures /non-diurnal/ and 
steep low level lapse rates by the afternoon hours. This should result in a 
changeover to all snow...with scattered to numerous instability snow/showers 
and occasionally heavy bursts/squalls possible over the 
west/central areas. Further south and east...cannot rule out some 
isolated low-topped convection as the NAM/WRF does show 100-200j of 
sb cape. This is not unlike the event that occurred 
yesterday...which produced gusty showers with embedded 
thunder sleet/snow and even hail. Strong divergence aloft associated with the ent 
region of a 135kt upper jet should aid in enhanced uvvel. A 
secondary wave prognosticated ride northeastward along the fnt may also act to 
increase precipitation amnts in this area. Overall...Thursday looks to be a 
fairly active day. 


Broad upper trough will align across the Great Lakes Thursday night 
into Friday. The cyclonic flow and cold temperature profiles will be 
supportive of bands of lake effect/upslope snow...as 850mb temperatures 
fall to -1 to -2sd blw normal /around -15c/. Northwesterly flow will back 
to more westerly by the end of the period...shifting axis of heavy snows 
more east of the lakes where long fetch trajectories may set up. 


Temperatures will generally range between 10 to 15 degrees blw normal on Friday. 


&& 


Long term /Saturday through Tuesday/... 
a clipper system looks to drop into the area Saturday night bringing 
a period of light snow to the area. It looks like a coastal low will 
also try to develop but this should stay well east of our area. So 
just expecting some widespread very light accumulations with the 
clipper with most of the snow ending by early Sunday. Behind this 
low winds will turn northwest allowing for some lake effect snow in 
northwestern areas and some terrain induced snows over The Laurels. 
However with a high pressure moving in Sunday night into Monday 
these snows should be rather light and short-lived coming to an end 
Sunday night. A more robust storm system should approach the area around 
Tuesday. Its still too early to determine precipitation types as models are 
not in agreement and will likely change several times over the next 
several days. Current runs are trending towards a warmer solution 
meaning an all snow event is not likely. With the departing strong 
high we may have to worry about low level cold air getting locked in 
leading to a wintry mix... but as mentioned this is still very 
uncertain. 


&& 


Aviation /00z Wednesday through Sunday/... 
stratus deck continues to linger...however is mainly at VFR 
status. A few marginal MVFR ceilings will linger through next few 
hours...but overall expect a gradual thinning of ceilings. Flow will 
gradually shift to southerly ahead of a strong cold front Wednesday evening. 
As flow strengthens from the south...llvl/S will steadily dry out 
and scour all low clouds. Wind gradient tightens around 3kft to 
15-20kts...although not positive mixed layer will bring down these 
winds at all sites...although looks pretty good for 
kbfd/kjst/kaoo between 15-22z. 


High level moisture steadily pools east ahead of approaching low 
pressure system. Frontal passage is questionable at this time...however 
based on hi-res local WRF/S best forecast is between 06-10z Thursday. Low level 
moisture will accompany front spreading at onset a mix of 
rain/snow and lower ceilings to MVFR/IFR. At kjst/kaoo/kbfd ceilings could 
fall to LIFR for a brief period Thursday...then improv to MVFR/IFR. 
Visibilities with snow showers will be frequently between IFR/LIFR in the 
heavier bursts. 


Lake effect snow showers and squalls could become a problem for 
the northwestern mountains and Laurel Highlands Thursday afternoon through Friday. 
Looks like the action gets going after 06z Friday...but some 
possible prior to this time. 


&& 


Ctp watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...rxr 
near term...rxr 
short term...steinbugl 
long term...steinbugl/chenard 
aviation...beachler/rxr