Thursday, August 24, 2017, 1:04 AM EDT
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Area Forecast Discussion
Valid At
Wed, Dec 31, 7:00pm EST
FXUS61 KCTP 240344

Area Forecast Discussion
National Weather Service State College PA
1144 PM EDT Wed Aug 23 2017

A large area of high pressure will build southeast across the 
region. An upper level disturbance will move across the central
and northwest mountains Thursday afternoon. Sprawling high 
pressure will then dominate the weather into the weekend.


Cyclonic flow aloft and a weak secondary cold front are
responsible for some light rain showers currently along and just
north of the NY border. The HRRR suggests one or two of these 
showers could survive the trek into the Northern Mountains, but 
the better bet is for them to continue to weaken.

Cold air in the form of 850mb temps as low as 6C (1-2sigma 
below normal) will slide across the Great Lakes and settle in 
for the next several days. Boundary layer decoupling will lead 
to calm air tonight which will help to maximize radiational 
cooling and help fog to form in the valleys, but some cloud 
cover over the west may keep the fog in check. Mins will range
from the chilly mid 40s over the north to around 60 across the


A potent albeit moisture starved shortwave trough will approach
the the area Thursday and Thursday evening. Some erosion in
stability is made to occur as the cold pocket aloft moves our
way during the afternoon. SPC does not have us outlooked for
thunder, but with such cold air aloft and the time of year, some
low topped storms would not surprise me. The chances are too 
low to include at this time. The best chance of showers look to 
be over the higher elevations of the west and north.
High temps Thursday will be about 5-6 deg lower than this 
afternoon's (Wed) values, or in the m60s NW-m70s SE PA.


An extended period of refreshingly cool, pleasant and dry 
weather will continue through the upcoming weekend as high 
pressure remains in control of the weather pattern over the 
northeast quarter of the CONUS. It will feel more like early
fall than late summer. A few spots in north-central PA could 
see morning lows dip into the upper 30s over the weekend. 

Global models suggest isolated, terrain-induced convection may 
be possible within return flow along the spine of the central 
Appalachians later in the period. However, ensemble means favor
a continuation of the mainly dry and seasonable pattern through
the end of August, as upper level ridging building into the 
Western U.S. supports troughing downstream over the central and
eastern states.

Interesting to note that the both the 12Z GFS/00Z ECMWF bring 
the remnants of Harvey toward the area by early September. 
After what appears to be a mainly dry end to the month of
August in central PA, this could be something to monitor down 
the road.


A ridge of high pressure over the region will ensure VFR 
conditions and light wind late this evening. Some patchy dense 
valley fog is likely late tonight, mainly in the valleys of 
northwest Pa. Based on latest SREF, downscaled NAM and LAMP 
guidance, believe a period of IFR/LIFR conditions is likely late
tonight into early Thursday morning at KBFD, with a brief 
period of fog also possible at KUNV/KAOO/KIPT around dawn. 
Elsewhere, believe MOS guidance is overly pessimistic at KJST, 
where radiation fog is rare due to its ridgetop location. 

Based on climatology and latest model guidance, believe most of
the fog across northwest Pa will burn off by around 14Z. There 
is high confidence in widespread VFR conditions the rest of 
Thursday. However, can't rule out a brief MVFR reduction from a 
passing shower in the afternoon.


Fri-Mon...Patchy AM fog possible, mainly northern Pa.




NEAR TERM...La Corte
SHORT TERM...La Corte/Lambert
LONG TERM...Steinbugl

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