309 
fxus61 kctp 211356 
afdctp 


Area forecast discussion 
National Weather Service State College PA 
856 am EST Sat Nov 21 2009 


Synopsis... 
high pressure should provide relatively dry weather over the 
region through Sunday. Easterly flow and a wave coming out of the 
Gulf should increase the chance of rain late Sunday into Monday. 
The pattern over North America is changing...the ensembles show a 
trough attempting to establish itself over eastern North America 
with a ridge over northwestern Canada. A series of waves will carve 
out the trough bringing unsettled weather to the region next week. 


&& 


Near term /until 6 PM this evening/... 
NAM BUFKIT profiles show a classic boundary layer inversion around 
the 296k to 298k levels across central and western PA between 3k 
and 5k feet. With center of 1023 mb surface high moving only slowly 
eastward across the Ohio Valley today...do not expect substantial 
enough mixing to clear the stratus from the central and south 
central mountains westward across the alleghenies...but there 
should be enough downsloping through the middle afternoon hours to 
produce numerous breaks in the stratus over the southeast... once 
the high cloud shield streams east of the area by early afternoon. 
Overall...a typical November sky across central PA. 


Core of the cold air at 850 mb associated with 500 mb trough aloft 
sinking southward verom the central and eastern glaks will drop 
south of the region by late this afternoon and evening...easing 
the low level lapse rates and helping to weaken the boundary layer 
inversion. Still expecting maxes to range from the upper 40s over 
the alleghenies...to the middle 50s aided by sunbreaks across the 
susq River Valley. 


&& 


Short term /6 PM this evening through 6 PM Sunday/... 
lg scale subsidence in wake of departing shortwave should result 
in clearing skies tonight. However...light winds associated with surface 
high should result in patchy radiation fog toward dawn. Although 
the clearing skies will allow temperatures to become cooler than this 
morning...mins still likely to be 5-10f above normal with readings 
generally in the M/u30s. 


After patchy am fog...ridging at surface and aloft should produce a mostly sunny 
and mild Sunday. Naefs supports the higher mav MOS temperatures...ranging 
in the l/m50s most spots. 


&& 


Long term /Sunday night through Friday/... 
an active split flow pattern is forecast to continue through much of the 
period by long term guidance. Several upper level troughs are forecast to 
traverse the Continental U.S. In both the northern and southern stream flow with 
varying levels of influence on PA. Overall however...most of the 
next week looks to be dry with continued above normal temperatures. 


The first trough...in the southern stream...is forecast to move across the Gulf 
Coast today...then lift NE along the middle Atlantic coast late Sunday. 
The wave will be lifting into the northern stream mean upper ridge with 
high pressure in place at the surface. Model trends are for a 
smaller...farther east solution of the surface low asscd with the southern 
trough and forecasts drier than pvs runs. GFS appears an outlier 
with a sig wet forecast for Monday across much of PA...and such 
have lowered probability of precipitation for this time period following the multitude of 
other long term guidance. 


Highest ensemble probability of precipitation are Monday during the day into Monday 
night. Some timing issues. Lowered the probability of precipitation into the 30-50 percent 
range Monday during the day and upped them Monday night into 
Tuesday due to the uncertainty in the timing. Pretty weak system 
and the rain should be very light. 


Amplification in the northern stream is forecast to occur over the Great 
Lakes by Tuesday...with a weakening surface front reaching western on Wednesday as 
supporting closed upper trough lifts into southeastern Canada. A stronger upper 
trough/cold front is forecast to move through PA Thanksgiving night...if 
current timing holds...with a noticeable cool down in store for 
shoppers next Friday. Any shower activity over northwest PA could be in 
the form of snow Thursday-Friday as 850 temperatures fall below 0c. 


&& 


Aviation /14z Saturday through Wednesday/... 
high pressure building into the region today. Moisture layer 
trapped under subsidence inversion will bring IFR/MVFR ceilings for 
several hours this morning in higher terrain tafs...but these 
should mix out to VFR by early afternoon. VFR will be the rule in 
the east with slight downslope component in light westerly winds. 


Outlook... 
sun...areas of MVFR/IFR ceilings early in higher terrain...otherwise VFR. 
Monday...MVFR local IFR. Possible rain showers in the afternoon. 
Tuesday...MVFR/IFR ceilings. Rain showers in the am. 
Wednesday...MVFR to VFR early. 


&& 


Ctp watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...grumm 
near term...Fitzgerald 
short term...devoir/Fitzgerald 
long term...grumm/gartner 
aviation...rxr