Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service State College PA
1024 PM EDT Thursday Apr 17 2014
A ridge of high pressure from the Canadian Maritimes down through
the Carolinas will keep fair and dry weather across most of the
region through Friday. A weak cold front will brush northwestern
Pennsylvania late tomorrow and tomorrow night. Another area of
high pressure will build east into the commonwealth for the
weekend. Temperatures will moderate this weekend and rise above
normal by early next week.
Near term /through Friday/...
Composite imagery is starting to show some low clouds forming over
the lower susq valley. Other than that...there are just some thin
high clouds streaming across. We will remain fair...but this
tendency for a moist maritime flow to help develop a shield of low
clouds will continue. We have a frost advisory in effect...but if
the clouds keep developing before the winds and temperatures drop
off...frost will not be an issue.
The expected clouds and higher dewpoints will help to curb the
temperature drop tonight...and mins early Friday will be several degrees
higher than earlier today.
Short term /Friday night through 6 PM Friday/...
the mean blyr flow veers a bit more to the south-southeast or south during
the day Friday...which will help an ill-defined warm front lift
north across the region and into New York state.
A broad...nearly north-south axis of low level moisture convergence
and higher dewpoints will help to create more in the way of strato
cumulus...than the nearly non-existent amounts that we/ve seen in the
unusually cold...and Bone-dry airmass the past few days.
Otherwise...the low level ridge axis stays in place along the middle
Atlantic Piedmont and helps to deflect a weak northern stream
system to our north. A significantly stronger southern stream storm
will also be held at Bay well to the south of the area. A few
light showers may graze the northwestern cos late Friday...or
Long term /Friday night through Thursday/...
the 17/12z medium range model and ensemble guidance has come into
much better agreement on the large scale pattern evolution across
the lower 48 this period...supporting increasing confidence in
the forecast. The main theme for central PA over the next 7+ days
will be a dry and relatively benign weather pattern...with no
significant rain-producing systems on the horizon. This should
contribute to increasing fire weather concerns. Temperatures will
moderate through next week...trending warmer with the odds favoring
a tilt toward the warmer-side of late April climatology.
Northern stream shortwave trough and surface cold front pushing eastward
from the Great Lakes region into the northeast states will bring
scattered...very light rain showers to northwest/N-central PA late Friday
night into early Saturday morning. Limited return flow and
relatively cool/dry airmass in place ahead of this system should
limit quantitative precipitation forecast amts to at or below 0.10 inch. Model consensus keeps precipitation
associated with closed southern stream low to the south of the
area...with Canadian high pressure regaining control of the
synoptic pattern through the remainder of Easter weekend.
Guidance temperatures appear marginal for frost sun-Monday morning
across the lower susq valley where the growing season is officially
The best opportunity/highest probability for appreciable rainfall
/0.25 to 0.50 inch amounts/ over the next 7 days will likely come
on Tuesday...with slightly better moisture in place ahead of an
approaching shortwave trough and surface cold front. The European model (ecmwf) is more
aggressive in bringing height falls into the northeast on day
7/Wednesday eventually closing off a 500mb low near southern New England.
Meanwhile the GFS/gefs are not as strong and generally more
progressive aloft...which leads to faster height rises heading
into the second half of next week. The sensible weather highlight
is probably a relative minimum in daytime high temperatures for
next Wednesday with both models/efs depicting a weak negative
500 mb-700 mb anomaly in vicinity of the New England coast.
Upper trough/closed low is prognosticated to migrate eastward across the northern
rockies into the upper Midwest Wed-Fri. Downstream ridge axis over
the Central Plains/MS valley/mid-south should reach the East Coast
by the end of next week. This suggests a warming trend following
the brief cool-down midweek with maximum temperatures possibly heading back
to/or above 70f.
Aviation /02z Friday through Tuesday/...
VFR conditions will continue through this evening. A layer of
shallow/broken MVFR-low end VFR stratocu will be sliding in from the
southeast overnight across the lower susq valley airfields...and
reaching the central mountains early tomorrow morning.
Mainly sunny skies will continue with southeast to south-southeast
winds averaging to 8-12 kts with occasional gusts around 20
kts. The wind will subside by 00z.
Chance for light rain to impact mainly northwest late Friday afternoon or
Friday night with low probability of restrictions. VFR elsewhere.
Friday...generally VFR. Areas of MVFR ceilings poss across central and southeast
Friday night-Sat...reduced ceilings/visibilities poss with chance of light rain
showers /mainly northwest half/.
Sun-Mon...no sig weather.
Tuesday...a few...to several-hour period of MVFR ceilings with brief MVFR
visibilities in showers accompanying a cold frontal passage.
frost advisory from 2 am to 8 am EDT Friday for paz057-059-
near term...la corte