Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
456 PM EDT sun Apr 26 2015
a slow moving upper level low over the northeastern United States
and cool air aloft will favor unseasonably chilly temperatures
with periods of showery weather through the end of this month.
Near term /until 6 am Monday morning/...
a sprawling upper low over the Canadian Maritimes will control the
pattern for the next couple of days at least. The main effect will
to funnel a series of upper shortwaves down out of New
York/eastern Canada and keep a fair amount of cloudiness and the
chance for showers in the forecast.
Early evening visible imagery showing expansive stratocu deck
associated with upper low extending from Ontario/Quebec into northern
PA. Band of lower precipitable waters seen in satellite imagery is resulting in only
scattered flat cumulus across central and southern PA. Have dropped mention
of sprinkles across the north...as nothing has developed as of 21z
and blyr will begin cooling/stabilizing this evening.
Scattered diurnal cumulus will likely dissipate across southern PA after
dark. However...low level instability beneath upper low will likely
sustain mcldy skies across the north mountains overnight. However...subtle
upper level ridging between shortwaves and cooling blyr should keep the
forecast dry tonight for nearly the entire area. Exception may be the
northwest mountains...where scattered shsnra appear possible around dawn associated with
approach of next shortwave.
Lows will range from around freezing over the northwest to around 40 in
Short term /6 am Monday morning through 6 PM Monday/...
models agree in bringing a relatively sharp shortwave down
through the eastern gr lakes and through the area Monday. Forecast
lapse rates aren't terribly impressive so the coverage of the quantitative precipitation forecast
may be a bit overdone. The sref/gefs have nothing more than a
small chance and that looks reasonable.
With marginally chilly temperatures in the low levels...can't rule out
some wet snowflakes if the showers manage to develop early enough
in the day over the northwest mountains no accums are anticipated.
Highs from the upper 40s to upper 50s will average well below
normal for the end of April.
Long term /Monday night through Sunday/...
active northern and southern stream split flow pattern across
North America will keep the region in upper level troffiness
through much of the coming week. This will support cooler than
normal...showery weather. Upper level ridging will move east and
try to persist over the eastern U.S. Starting around next
Early this week a shot of cool unsettled weather arrives as a
back door cold front is nudged southward across PA from an upper
low over new eng. Cool temperatures aloft associated with upper low will likely
lead to a good deal of daytime cloudiness and scattered rain showers /esp over
the mountains/ Monday and Tuesday.
By midweek...slow moving southern stream upper low will emerge into the
southeastern to Middle Atlantic States...possibly phasing with a northern stream
wave. At this point significant precipitation looks to stay south of
PA...though the hiest probability of precipitation of the period will be from this system
on Thursday. Regardless...Thursday looks to be a cloudy and cool
day across the commonwealth.
Affects of this upper low should diminish through Friday into
Saturday and with rising heights the start of next week looks
warmer and drier...at this point.
Aviation /21z Sunday through Friday/...
widespread VFR conditions with high based ceilings over mainly
northern areas as a weak disturbance drops south out of New York.
Ceilings will lower across the northern mountains and Laurel
Highlands tonight with MVFR conditions developing by midnight in
the vicinity of Bradford and after midnight at Johnstown.
Scattered light rain/snow showers will also move into these areas
from the north...probably not until sunrise or shortly after.
Elsewhere... conditions should remain VFR through Monday.
Tuesday...mainly VFR with scattered light rain showers.
Wednesday...no sig weather.
Thu-Fri...MVFR possible in scattered rain showers.
near term...Fitzgerald/la corte
short term...la corte