653 
fxus61 kctp 181908 
afdctp 


Area forecast discussion 
National Weather Service State College PA 
308 PM EDT Friday Jul 18 2008 


Synopsis... 
high pressure along the middle Atlantic coast will continue to 
provide very warm and humid conditions by day...with mainly clear 
and muggy conditions at night...right into Sunday. Very 
isolated...late afternoon and evening showers and thunderstorms 
will occur today and again Saturday afternoon and evening. A 
trough of low pressure and associated cold front will approach the 
area from the west late Sunday into Monday...triggering a more 
significant round of showers and thunderstorms. Slightly cooler 
temperatures and lower humidity will move into the region behind 
the front for later Monday and Tuesday. 


&& 


Near term /until 9 PM this evening/... 
convective temperature in the middle 80s recently exceeded across the ridges 
has helped to anchor a few...nearly stationary pulse thunderstorms and rain across 
our SW zones and over the lower susq valley. We'll see similar 
convective development during the middle to late afternoon hours 
elsewhere across the central and north. 


Without the more organized mesoscale forcing we had yesterday 
(near the intersection of a westerly low level jet and surface front) expect 
practically all of these storms to be more transient as elevated 
rain cores collapse quickly through the updraft. Based on the 
depth of the positive area on the sounding above the -20c 
level...there still could be one or two select cells that can tap 
the near 2000 j/kg or cape and produce a brief microburst between 
40-55 miles per hour and hail at or below 1/2 inch. 


&& 


Short term /9 PM this evening through Saturday night/... 
convection will dissipate quickly before dusk leaving near calm 
air and haze...thickening to areas of 1-2sm valley fog during the 
early to middle morning hours of Saturday. 


Dewpoints should remain in the 60s (to near across the se) leading 
to another warm and muggy night. Mav MOS guidance continues to be 
at least a few degree f too low with dewpoints (and thus min forecast 
temps)...mainly across the central and southeast zones. Will maintain 
previous shifts trend toward the warmer mins via the met MOS. Lows 
will dip to around 60 across the northwest mountains...and will range from the 
middle 60s to lower 70s across the central and southeast. 


Sref data suggests most of central PA should stay dry on 
Saturday. However...isolated to scattered diurnal convection will remain 
possible along the northern tier counties...given the proximity of a quasi 
stationary frontal boundary and embedded short waves translating west to 
east along the southern edge of the westerlies. The second area of middle 
to late afternoon convection will be across the central and lower 
susq valley where mixed layer cape will be between 1500-2000 j/kg. 


Ens mean 850 temperatures suggest heat will continue unabated with maximum 
temperatures 5-10f above normal...ranging from the middle 80s north mountains...to 
the middle 90s over the lower susq valley. 


&& 


Long term /Sunday through Friday/... 
the long term should start with a rather zonal flow aloft...but a 
trough should develop rather quickly over the northeast and Great 
Lakes during the first few days of the week. Guidance differs 
significantly on the longitude and orientation of this troffiness. 


In response to the digging/developing trough...a wave develops over 
the upper Great Lakes on Sunday and brings a weak front down into 
the soup in place locally Sunday evening/night. Showers and 
thunderstorms are almost likely later sun/Sun night...given timing 
and NE-SW orientation of the front. But...will keep likely probability of precipitation up 
in the north/west for now. 


Showers could linger Monday...depending on timing of the front. 
Surface ridge moving in from the Great Lakes/Ontario should push the 
front through just enough to help Tuesday/Wed/thurs stay generally dry 
and slightly cooler than normal. However...the front won't go too 
far to the south. An mesoscale convective system could try to impinge from the west Tuesday 
night/Wednesday morning per a very feedback-laden GFS solution. This is a low 
probability forecast at this point/time-range...so will keep just a low chance 
pop in for later Tuesday into Wednesday am. 


There may be a higher chance for precipitation across the area very late in 
the week...especially across the south as the front nears from the south. 


&& 


Aviation /19z Friday through Wednesday/... 
visibilities expected to be mainly 6-8sm into early tonight with very 
isolated IFR/MVFR ceilings/visibilities in slowly east to NE moving pulse 
thunderstorms and rain. Similar conditions will occur again Sat afternoon and evening. 


Skies will become mainly clear from 00z through 15z Sat with areas 
of MVFR fog and haze. Winds will be 4-8 kts from the west to SW 
into early this evening before becoming nearly calm later tonight 
through middle morning Sat. 


High pressure center near the middle Atlantic coast will remain in 
control of the local weather into Sunday...bringing another night 
of mainly clear skies and near calm wind Sat night. 


Best chance for rain showers/thunderstorms and rain and localized IFR flying conditions will 
be during the late weekend through Monday as a frontal boundary slips 
across the middle- Atlantic region. Cumulus field will increase 
Fri/Sat...with some reduction to ceilings/visibilities anticipated this 
weekend from any convection that may dev and produce VFR to tempo 
MVFR/IFR. 


&& 


Ctp watches/warnings/advisories... 
none. 


&& 


$$ 
Synopsis...Fitzgerald/Lambert 
near term...Fitzgerald/Lambert 
short term...Fitzgerald/Lambert 
long term...dangelo 
aviation...Lambert/rxr