Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
842 am EDT Thursday Oct 2 2014
a ridge of high pressure will build over central PA today.
A strong cold front will sweep across the region Friday
night. A deep upper level trough will then remain parked over
the northeast Continental U.S. Through early next week.
Near term /until 6 PM this evening/...
830 am update...
tweaked sky and fog a little based on latest viz shots.
11.3.9 micron imagery showing widespread low clouds/fog across
central PA. Lack of mixing beneath surface ridge axis...combined with
lowering October sun angle...will likely result in the low
clouds/fog persisting in some spots until early afternoon.
Model sounding do imply a brighter afternoon...with pt-mostly sunny skies
likely. With upper level ridging overhead...have kept probability of precipitation near zero
today. Ens mean 925 temperatures between 14-18c should support highs this
afternoon in the l70s most spots...with the warmest readings relative
to normal over the Allegheny plateau.
Short term /6 PM this evening through Friday night/...
surface ridge extending from the Canadian Maritimes southward along the East
Coast will keep central PA dry tonight. However...moist southeasterly flow
combined with radiational cooling of blyr should once again lead
to developing stratus across central PA late tonight. Higher than
normal dewpoints will lead to a mild night for early October with lows
mostly in the l/m50s.
Models have come in line with timing of strong cold front Friday
night. Deep southerly flow in advance of cold front draws a plume
of anomalous precipitable waters /2-3sd above normal in the 00z gefs/ into
central PA Friday night. Given the moisture and lg scale forcing
implied by model 500-300 q-vec convergence...have raised probability of precipitation to
around 90 percent Friday night. All plume members of the sref and gefs
are indicating measurable rain Friday night.
Long term /Saturday through Wednesday/...
model spread remains low through the weekend...all indicating cold
front exiting eastern PA around 12z Sat. Can/T rule out lingering
rain showers around dawn. Otherwise...surface ridging and arrival of much drier
air should translate to a dry weekend. Model blyr wind fields all
indicate lake effect rain showers should remain north of the
border...but have kept a slight chance of rain showers over northwest Warren Colorado.
Ens mean 850temps indicate this will be the coolest weather since last
Spring with maximum temperatures from only near 50f over the high terrain of
the alleghenies...to the l60s across the lower susq valley. Looks
like surface high will not pass over the region...so conds not ideal
for rad cooling...but can/T rule out frost/freeze issues Sat or
Sun night over the alleghenies.
Increasing model spread/forecast uncertainty early next week.
However...expect a warming trend as flow becomes southerly ahead
of digging trough over the great lks/Midwest. A period of showers
appears likely sometime early next week...as upper trough lifts
through. However...can/T go more than low chance of precipitation on any day
due to timing and strength uncertainties.
Aviation /13z Thursday through Monday/...
12z tafs sent. Conditions going between low ceilings and areas of
dense fog. Light southeast flow.
Light east/southeast wind does not Bode well for quick clearing/dissipation
of the fog and any morning stratus after sunrise. But by late
morning conditions will evolve to VFR.
A very strong upper level trough will drop down through the upper
Midwest and Ohio Valley on Friday...and bring a strong cold front
through Friday night. Preceding the front will be a srly wind
which could make low level wind shear on Friday....but gusts will be more-likely
as mixing brings those strong 30-35kt winds down. Thunder is
expected late Friday and through Friday night. Showers may linger Sat am
in the east.
Sat...am showers eastern areas. Breezy with improving conditions east of
the mountains isolated showers and MVFR ceilings over North/Western areas.
Sun-Mon...MVFR ceilings possible northwest...otherwise VFR.