737 
fxus61 kctp 061201 
afdctp 


Area forecast discussion 
National Weather Service State College PA 
801 am EDT sun Jul 6 2008 


Synopsis... 
a trough of low pressure in the upper atmosphere will drift slowly 
east from the middle Ohio River valley today...crossing Pennsylvania 
Monday afternoon and night. Warm and more humid air will spread 
north into the commonwealth and interact with a meandering surface 
front to bring numerous afternoon and early evening showers and 
scattered thunderstorms today. It will stay quite warm and humid 
into Tuesday with a chance for mainly afternoon showers and 
thunderstorms. A cold front will sweep across the state 
Wednesday...accompanied by a round of showers and scattered strong 
to severe thunderstorms. A cooler and drier airmass with clear to 
partly cloudy skies will move into the region for Thursday and 
Friday. 


&& 


Near term /through tonight/... 
weak high pressure along the Penn New York border was maintaining 
clear to partly cloudy skies over much of the region early this 
morning with relatively cool temperatures and dewpoints in the lower to 
middle 50s across northern Penn. Clouds increase toward the Mason/Dixon 
line (with temperatures in the 60s) in the vicinity of a pesky...quasi 
stationary boundary that's resided over that area for the past few 
days. 


A fairly amplified and slow moving upper trough across the lower 
and middle Ohio River valley this morning will help to push this 
moisture northward into the County Warning Area (with precipitation water values around 1.5) this 
afternoon. Operational NAM...GFS and 21z sref all show the left 
exit region of a 60-70 knots 250 hpa jet maximum lifting north-northeast across 
central Penn and the Allegheny plateau region around peak heating 
this afternoon. 925-850 hpa Theta-E convergence...coolest middle 
level temperatures...and greatest amount of insolation to destabilize the 
blyr layer are all found across the northwest half of the County Warning Area as this 
upper level forcing increases across the region. This could be 
similar to the surface/upper levl setup we saw Saturday 
morning...that led to locally heavy...1-2 inch rainfall across 
the Laurel Highlands and portions of central mountains 


Based on the above model fields...will paint 2 areas of higher 
probability of precipitation...near the Allegheny Front (where mixed layer cape could 
climb to near 1500 j/kg)...and also across the lower susq valley 
(based on the close proximity of the surface front and precipitable waters  just over 
1.5 inches). Day shift can fine tune the timing and may have to 
increase the probability of precipitation in some areas to near categorical for the middle to 
late afternoon. 


Maximum temperatures today will be near normal (in the u70s across the 
mountains...to lower and middle 80s over the lower susq valley). 


Convection will gradually diminish this evening...but will 
maintain isolated to scattered showers through Monday morning. 
Min temperatures early Monday should be 3 or 4 f warmer in most places 
compared to this morning. 


&& 


Short term /Monday through Monday night/... 
weakening upper low and slightly cooler middle level temperatures crossing 
the region Monday and Monday night will lead to partly to mostly 
cloudy skies with a chance for mainly afternoon and early evening 
showers and thunderstorms and rain. Highest precipitable water air and best upper jet dynamics 
will shift east toward the middle Atlantic coast...so highest "chc" probability of precipitation 
will be kept across the southeast third of the County Warning Area. 


Maximum temperatures will be a few degree warmer than today...or in the lower to 
middle 80s across central and northwest Penn...and possibly reaching 86-88f 
across the lower susq valley. 


&& 


Long term /Tuesday through Saturday/... 
zonal flow is forecast over the Continental U.S. Through the period with a 
strong jet riding the northern border states and weak upper ridging 
with little flow over the southern U.S. 


The jet is forecast to buckle a bit and bring a cold front through the 
NE on Wednesday. Warm and humid conditions will precede the Wednesday 
frontal passage along with the daily threat of showers and thunderstorms. 
Maximum temperatures are forecast to be around 5 degrees above normal Tuesday 
and Wednesday. The warmest day should be Tuesday as the low level flow 
veers more to the SW or west ahead of the cfront...pushing temperatures 
well into the 80s...to around 90f in the southeast. 


The front will bring a brief cool down...with near normal or 
slightly below normal temperatures forecast for Thursday and 
Friday. Hot weather will return for next weekend as heights rise 
and the 588dm height contour pushes north into PA. 


&& 


Aviation /12z Sunday through Thursday/... 
WV Sat imagery shows compact upper level disturbance drifting southeastward 
in vicinity of of Ohio/KY/WV borders. A west to east oriented surface frontal boundary 
extends along the PA/Maryland border. To the north...elongated hi pressure 
area remains in place from the lower glks Wednesday into New England. 


Moist low level airmass across S/central PA with surface dewpoints in the 
60s combined with southeasterly upslope component to the low level flow has 
resulted in dense fog /LIFR/ and St formation /cigs blw 500ft/. 
Drier air to the north has kept bfd VFR. As the boundary layer 
begins to mix out...xpect steady improvement to VFR by 15-18z. 


The nearly stationary frontal boundary in vicinity of PA/Maryland border will lift northward 
today as the aforementioned upper level wave moves into the central 
Appalachians. Hi res models devlp scattered convection this afternoon/evening 
across much of scent PA as the moist boundary layer is heated by 
afternoon sunshine. This will likely lead to scattered-numerous cvg of 
airmass/pulse type rain showers/thunderstorms and rain after 18z with the highest 
probabilities over the southern airfields. Have added in thunderstorms in the vicinity into jst- 
aoo-MDT and kept cumulonimbus at unv/ipt. Added cumulonimbus mention at bfd...however 
precipitation chances generally decrease from south to north. Decided 
against tempo groups beyond 6hrs...but xpect local MVFR/IFR conds in 
heavy downpours where thunderstorms occur. Fog will likely become an issue 
again tonight given residual low level moisture and some partial clearing. 


Looking out to next week...area should remain susceptible to scattered 
diurnal rain showers/thunderstorms and rain activity into Tuesday with mainly VFR conds during the 
day and fog issues at night. Cloud frontal passage forecast middle-week with frontal 
precipitation and MVFR conds. Hi pressure forecast to move in behind the fnt 
Thursday/Friday with a return to VFR. 


&& 


Ctp watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...Lambert 
near term...Lambert 
short term...Lambert 
long term...gartner/Martin 
aviation...steinbugl 

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