Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
146 PM EDT Tuesday Jul 22 2014
A cold front will move across the commonwealth late Wednesday and
Wednesday night. A refreshing cooler and less humid airmass will
overspread the commonwealth for the end of the week into the
Near term /through tonight/...
Convective mixing has led to the demise of the low cloud
shield...but now we are seeing more cumulus form. Satellite and
radar indicate a couple of small showers trying to get going in
the warm humid airmass...but the warm dry air aloft is so far
keeping activity mainly capped.
Mesoscale anal shows a tongue of MUCAPES exceeding 2000j nosing into
southwestern PA but also indicates very warm middle level air pushing into
the area. This will help suppress activity despite the
expectations of a fair amount of available instablity this
afternoon. The best chance for the isolated convection would seem to
be over southern areas east to the lower susq valley where
slightly cooler middle level temperatures are forecast to persist.
Afternoon highs will be noticeably warmer than previous
days...topping out near 90 over the southeast and in the middle 80s over the
The overnight will be similar to last night...dry but with patchy
low clouds and fog forming after midnight. It will be a humid
night for sleeping.
Short term /Wednesday/...
A dry start to the day Wednesday will give way to increasing
chances for showers and thunderstorms as forcing increases
associated with the approaching cold front. We are not outlooked
for severe at this time but the airmass change will be fairly
Stark for middle July and forecast convective available potential energy in excess of 1200j suggest
Storm Prediction Center might expand their slight risk with later updates. Either way
it looks like an unsettled and wet day as the front traverses the
Thanks to a warming low level west-southwest downslope flow ahead of the
cfront...high temperatures Wednesday will be the warmest of the week...ranging
from the lower 80s across the highest terrain of the north and
west...to the middle and upper 80s in the Central Valley...and lower
90s in the greater York/Harrisburg area.
Long term /Wednesday night through Tuesday/...
overall scenario remains unchanged in the long term period as a
large upper ridge building over The Four Corners region is
forecast to expand north and east into The Rockies and plains
during the period. Downstream...this will lead to long wave
troffing over the eastern third of the country. Upper low to the
east of Hudson Bay will be strengthened at times by shortwave
energy in the stronger jet stream flow across Canada. Southward
extension of this low/trough will at times during the period
strengthening the troffing across the northeastern U.S./Our
region. Todays trend of medium range model guidance is for
stronger/deeper troffing downstream across the eastern
u... an almost full latitude trough extending from the
eastern Canada low southward to Florida. This will likely serve to
expand and prolong the chances for precipitation this weekend.
Guidance forecasts continue to bring a front and increased
changes for precipitation toward PA in the Wednesday/Thursday time
frame and show a second...potentially stronger system late next
weekend. The trend of stronger troughing mentioned above has lead
to slower arrival and departure of the frontal system in the daily
forecasts. A warm front will be on the doorstep of PA Sunday
morning...a bit slower than forecast yesterday. Have thus adjusted
probability of precipitation/time to suit. Associated cold front does not cross the
state until Monday at this point...leading to a potential prolonged
period of showers and thunderstorms. At this time frame
however...a lot will likely change before we reach next weekend.
Aviation /17z Tuesday through Saturday/...
All terminals are VFR at this hour...and will remain into the
evening. Warming temperatures aloft and lack of strong forcing suggests
very low chances of afternoon pop-up showers or thunderstorms. No
mention of thunderstorms in tafs as point probs/precipitation covering will be
very low/sparse. The best chance of a shower or thunderstorm will
be south of I-80 into the evening.
Diurnal cumulus should fade after dark with some patchy fog and associated
lower ceilings/viz re-developing overnight.
Wednesday will feature a strong cold front passing through the
area along with numerous showers and thunderstorms. Terminals will
be mainly VFR but with impacts increasing along with the coverage
of the showers and storms..especially in the afternoon and
Thursday...scattered thunderstorm impacts possible southeastern airfields as cold front slows
along the middle-Atlantic coast.
Fri-Sat...patchy a.M. Fog. Otherwise no sig weather.
near term...la corte
short term...la corte