613 
fxus61 kctp 212354 
afdctp 


Area forecast discussion 
National Weather Service State College PA 
654 PM EST Sat Nov 21 2009 


Synopsis... 
high pressure will provide fair weather through Sunday night. 
Stubborn cloudiness will finally give way to sunshine over most 
sections on Sunday ahead of a weather system that promises to 
bring rain statewide on Monday. This system will be followed by a 
series of disturbances which are expected to bring cooler weather 
to the region for the Holiday and through the Holiday weekend. 


&& 


Near term /until 6 am Sunday morning/... 
NAM BUFKIT profiles continue to show a classic boundary layer 
inversion around the 296k to 298k levels across central and 
western PA between 3k and 5k feet this afternoon. At the same time... 
as center of 1023 mb surface high moves only slowly eastward across the 
Ohio Valley...core of the coldest air at 850 mb associated with 500 mb trough 
aloft is sinking southward towards The Laurels. Any breaks in the 
overcast that do form from the central and south central mountains... 
laurels...extending northward across the northern tier quickly fill in 
as a result of the low level instability. However...there is 
enough downsloping in the north-northwest flow across my southeast counties to 
keep p/c conds in place through tonight. 


As the cold air departs tonight...NAM forecast soundings indicate 
the inversion weakens...although will have to deal with the 
typical diurnal surface cooling and shallow overnight inversions early 
on Sunday before better mixing and brighter skies prevail for 
most. 


&& 


Short term /6 am Sunday morning through Sunday night/... 
morning patchy fog will dissipate by middle to late morning...and 
with continued ridging surface and aloft...expect skies to become 
partly to mostly sunny everywhere with a milder afternoon. 
Naefs gives higher mav MOS temperatures...ranging in the l/m50s most 
spots. 


Expect increasing low level moisture from deep east/southeast flow 
Sunday night as surface ridge tracks towards Newfoundland bringing a 
large over water fetch into the Middle Atlantic States. At the same 
time...a decaying upper wave impinging upon the upper ridge from 
the west over the Ohio Valley will spread deeper layer moisture 
across the region by late Monday. The result will be a slight 
chance of light rain by dawn Monday...with much better chances 
later Monday as the cad is well established below warm air advection aloft. 


&& 


Long term /Monday through Saturday/... 
models have weak system lifting NE from the Gulf area later on 
Monday into Tuesday. Did slow things down some and think bulk of 
any rain would hold off to after. Did cut probability of precipitation back some. Expect 
amts to be on the light side. 


Some clouds and light rain...drizzle for the most part...could 
linger into Tuesday. 


Quite a bit of variation in model solutions. Could see northern 
and western areas staying dry. 


For Wednesday...central PA is between systems. GFS looks fast... 
HPC not as fast... weighted forecast to slower speed. 


Overall...only made a few minor changes to the package. 


For Thursday into Sat...temperatures cooling off closer to normal...as 
ridge builds across the western states...and more of a trough 
pattern prevails across the eastern states. Some rain and 
snow showers will be possible across the mts Thursday into Friday. 


Enough ridging may take place on Saturday...to keep most of the 
area dry. 




&& 


Aviation /00z Sunday through Thursday/... 
infrared imagery indicating considerable stratus holding onto the atmos 
over PA...expect for the susq-valley where it remains few/skc. 
Guidance suggests as flow turns north/NE boundary layer will dry and erode 
stratus deck between 09-12z. A few locations could see patchy fog 
dev...however expect this to be local. Elsewhere anticipate skies to 
bounce to VFR conds and persist through 00z Monday. 


Outlook... 
Monday...MVFR local IFR. Possible rain showers in the afternoon. 
Tuesday...MVFR/IFR ceilings. Rain showers in the am. 
Wednesday...MVFR to VFR. 
Thursday...MVFR with chance -shrasn. 


&& 


Ctp watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...devoir 
near term...devoir 
short term...devoir 
long term...Martin 
aviation...beachler