980 
fxus61 kctp 030642 
afdctp 


Area forecast discussion 
National Weather Service State College PA 
142 am EST Wednesday Dec 3 2008 


Synopsis... 
a ridge of high pressure will build along the East Coast 
today...and be followed by a strong cold front on Thursday. 
Lake effect snow showers will prevail across parts of western and 
northern Pennsylvania on Friday into Saturday ahead of an Alberta 
clipper which will spread light snow or snow showers across the 
area later Saturday into Sunday. 


&& 


Near term /until 11 am this morning/... 
stratus has eroded over the central and southeastern two thirds of 
central PA. Thanks to strong surface ridging extending from the 
central Appalachians to northern New England. Scattered to broken low 
clouds are continuing to thin from The Laurels northward across the 
northern tier. Should be a nice sunrise for most this morning... 
and a pleasant morning. 


&& 


Short term /11 am this morning through Friday night/... 
brief period of milder weather is in store for later today and tonight... 
eventually yielding to increasing clouds after 00z this evening 
ahead of the approaching frontal system to cross the area on Thursday. 


Increasing clouds early tonight will make min temperature forecast 
difficult. Am remaining slightly above guidance for tonight...but 
a few hours' difference in the amount of cloud cover would be 
problematic. Will increase from slight chance to likely probability of precipitation 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 Monday...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 /07z Wednesday through Sunday/... 
a few more hours of SC...then clearing with VFR conditions 
today. Overall...a nice day...with mild temperatures for a change. 


A cold front moves in late tonight...early Thursday...expect a 
few rain showers. Dry slot behind front. This along with 
shear...will limit lake response for a while. Was concern 
last night that significant squalls could occur after 06z 
Friday... but this does not look to be the case now...as 
shear decreases...heights come up. Thus much of the period 
Friday into Sunday may be dry and VFR. Overall...a fairly 
dry pattern this fall so far. 


&& 


Ctp watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...lacorte/devoir 
near term...lacorte/devoir 
short term...devoir/steinbugl 
long term...steinbugl/chenard 
aviation...Martin