Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
512 am EDT Friday Jul 11 2014
the upper air flow will become westerly this weekend. Temperatures
will be seasonable today but become hotter on Saturday and
Sunday. Despite the influence of high pressure at the
surface...the area will remain vulnerable for isolated showers and
thunderstorms to pop up each afternoon off the high terrain.
Higher chances of storms are expected Monday and Tuesday as a
very strong trough of polar air will push southward into the Great
Near term /until 6 PM this evening/...
fog beginning to show it/S hand...developing in the cool sinks
where the rainfall occurred yesterday. Visbys will gradually
decline in many spots across the southern half of the region...where
the ambient moisture is highest. The fog will burn off by 9 am as
the atmos mixes quickly under otherwise sunny skies. The very dry
/for July/ dewpoints near 50f in the northern tier will most
likely rise a bit this morning. The pattern of convective clouds
popping up late morning over the high terrain of the alleghenies
will happen once again today. A subtle short wave feature over the
northwest this morning will slide east and will likely cause the
short cumulus to grow bigger and produce isolated T/rain showers in the afternoon. It
may also help some rain showers grow in the southeastern part of the area - again
mainly off the elevated heating surfaces - and drift eastward.
Temperatures will probably be a little more homogenous today- the drier
air over the northwest will be heated easily by the July sun...and more
clouds over the southeast in mid-day/afternoon will cut a degree or two off
yesterday/S maxes there.
Short term /6 PM this evening through 6 PM Saturday/...
afternoon convection will wane very quickly as we will be in the
unfavorable wake/height bump/subsidence of a weak short wave.
Will chop the probability of precipitation off after sunset...but it may happen earlier.
Mins tonight will be similar to this morning. Saturday looks like
there could still be a few rain showers around. Will keep on with the
idea of terrain induced rain showers. No big changes to the airmass...nor
to the upper pattern/temperatures through the short term. But the surface
high does slide to the shore and allow more southerly winds.
Thus...temperatures should get hotter for Sat. U80s are expected in the
Long term /Saturday night through Thursday/...
stalled front along the southeast coast should pivot back northward as
warm front Sat night into early Sunday with S-southwesterly low level jet increase low level moisture
flux through the upper Ohio Valley into western PA in advance of lead
shortwave energy and associated surface cold front moving southeastward across the great
Amplification of the upper pattern begins early next week with a
model consensus generally indicating a frontal precipitation axis shifting
southeastward through the Great Lakes/Ohio Valley regions into central PA sun-Mon.
Although predictability is too low at this time...a severe weather threat
should spread southeastward in time from the upper Midwest/Great Lakes/Ohio Valley
into the middle Atlantic and northeast states...along southern periphery of
stronger winds/cyclonic flow aloft and several reinforcing cold
frontal surges associated with the amplifying synoptic upper
trough. Each cold frontal surge will provide an opportunity for
showers/thunderstorms through at least Tuesday.
The highly anomalous amplification of the large scale pattern is
a virtual lock by the end of the period as indicated by all medium
range global numerical models and ensemble systems. This well-
advertised high meridional event will feature a full-latitude
ridge and searing heat out west...not be be outdone by the return
of the polar vortex in the east over Quebec/ont and the upper Great
Lakes. Considering the magnitude of the upper level trough with
500mb standardized anomalies on the order of -3 to -4sd in both
the deterministic global models and their respective ensemble
means...confidence in a period of below average temperatures /during what is
climatologically the hottest time of the year/ is very high from
Tuesday-Thursday of next week.
Aviation /09z Friday through Tuesday/...
mclear skies...a light wind and wet ground from yesterday/S
rainfall has resulted in areas of fog this morning across mainly southern
PA. It appears kunv...kaoo and perhaps klns will experience a
period of IFR/LIFR visibilities early this morning...then rapid
improvement expected...as fog Burns off around 12z.
With high pressure over the area...there is a high confidence in
widespread VFR conds and light wind the rest of today.
Sat...no sig weather expected.
Sun-Tue...brief...mainly PM...thunderstorm impacts possible.