Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
514 am EDT Friday Jul 25 2014
High pressure will drift east and maintain fair weather today. The
weather pattern will become unsettled once again as a series of
disturbances approach the area beginning Saturday...and continuing
through Monday. A deep upper trough will move into the eastern US
next week bringing another shot of unseasonably cool temperatures
to the region.
Near term /through tonight/...
Today will be the last fair day for a while as high pressure
builds across the forecast area. Other than some thin high
clouds...and possibly some smoke from western Forest fires...we
will have a sunny and very pleasant day with highs generally in
the 70s to lower 80s. Dewpoints in the 40s will be unseasonably
Dewpoints will slowly start to creep back up tonight as the high
slips off to our east and we begin to see a return southerly flow
develop. Other than a very small chance of a shower making it into
the far northwest by morning...it will remain dry.
Short term / Saturday through 6 am Sunday/...
Saturday will start off dry in most areas. Timing and placement
of eventual convection will be very dependent on upstream
developments as we come under a robust west-northwest flow aloft. In response
to the approach of a strong upper jet streak nosing into the lower
lakes by late in the day...short range operational models and
ensemble packages agree in developing an anomalously strong west-southwest
low level jet and surging it into the region...especially during
Saturday afternoon. Moisture initially looks limited...helping
temper how much instability we will experience. I leaned away
from the very wet sref probability of precipitation...using a blend of model guidance to
come up with just a chance of showers and storms...the better
chances being in the afternoon.
Highs Saturday will be very pleasant from the middle 70s northwest to middle 80
southeast...but dewpoints will begin creeping up bringing humidity back
into the noticeable range.
Long term /Sunday through Thursday/...
Storm Prediction Center shows a slight risk from the Central Plains into western PA
for their day 2 outlook. They seem to be keying on a secondary
even stronger disturbance that will be dropping into the upper
Midwest...eventually sparking off an mesoscale convective system that could affect the
area late Saturday night and early Sunday.
Latest timing has Sunday being somewhat in between systems as the
expected mesoscale convective system mentioned above fades and mainly moves south of the
region. Lacking confidence in precipitation timing or placement...I kept
probability of precipitation in the chance range given the steadily falling upper
heights...a tad below most guidance.
Highs Sunday will still be in the 70s and 80s...but will represent
a downward trend that we will see for the upcoming week as an
anomalously deep upper trough takes aim at the eastern US.
By the time we get into Sunday night and Monday...there are
differences in timing and strength of a surface low that comes
along with the deepening upper shortwave. The GFS/gefs show a
stronger system and imply we could be dealing with a strong
mesoscale convective system/slug of heavy rain. The sref is less defined since the NAM
wants to break surface developments into pieces northwest and southeast of the
area. The European model (ecmwf) is more in line with the gefs/GFS and a single
stronger low...but is slower. This timeframe seems to represent
the period of highest confidence for rainfall so likely MOS probability of precipitation
By early next week...a deep upper trough will help deliver another
chilly airmass that will last for much if not all of the week.
Gefs shows 500 heights some 3-4 Standard dev below normal developing
and settling down over the Carolinas through Wednesday...before
the trough is made to begin filling and slowly lifting out. It
should equate to several days with little or no rain and
temperatures running several degrees colder than normal for the
end of July.
Aviation /08z Friday through Tuesday/...
06z tafs sent.
High pressure and associated dry air mass will result in a near
certainty of VFR conds and light wind for almost all of central PA
overnight. The exception will be the deep valleys of the
alleghenies...where unseasonably cool temperatures combined with Warm
River/stream water and a calm wind...will result in locally dense
fog a few hours either side of dawn. Climatology and latest MOS
guidance indicate kbfd is the only airfield likely to experience a
period of low visibilities...while a slight chance exists at kunv...kaoo
Any early valley fog should burn off by 14z...then a near
certainty of VFR conds/light wind for the rest of Friday as high
pressure drifts over the state.
Sat...scattered thunderstorms and rain impacts possible...especially northwest mountains
sun...am low ceilings poss northwest mountains scattered thunderstorms and rain impacts poss southern PA.
Monday...oncl visible restrictions poss in shra/tsra.
Tuesday...no sig weather expected.
near term...la corte
short term...la corte
long term...la corte