Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service State College PA
339 PM EDT Thursday Apr 17 2014

Synopsis...
a ridge of high pressure will extend from the Canadian
Maritimes...southwest to the middle Atlantic coast...keeping fair and
dry weather across most of the region through Friday. A weak cold
front will move east from the Great Lakes region and brush
northern and western Pennsylvania with some clouds and perhaps a
few rain showers late Friday and Friday night. Another area of
high pressure will build east into the commonwealth for the
weekend supply another few days of pleasant Middle Spring weather.
Temperatures will moderate further this weekend and rise above
normal by early next week.

&&

Near term /through tonight/...
variable amounts of mainly thin cirrus will occur across central
and northwestern Penn for the rest of today...accompanied by a
southeasterly wind of 10-12kts with gusts of 15-20kts in many
locations.

Although winds are similar to yesterday /albeit from the opposite
direction/ mother nature is less deceiving with respect to
temperatures...which are 8-10f warmer in all locations compared to this
same time Wednesday.

Some low level marine moisture /the bulk of it which is still lurking
along...and off the southern New Jersey and Delaware-Maryland-Virginia coast/ is continuing
too advect northwest and across the lower susq valley. The extent of
these shallow...sct-bkn strato clouds should continue to increase
and cover most of the region along and to the southeast of I-81 by dusk.

Temperatures remain on track to reach middle to late afternoon highs in the
low to middle 50s.



As the relatively shallow vertical mixing subsides this
evening...we should see the strato cumulus deck across the lower susq
valley and adjacent southeastern and ecent PA solidify into a more
uniform broken- overcast cloud layer and advance into the Central Ridge
and valley region as the mean surface-850 mb flow remains from the
southeast.

Elsewhere...periods of cirrus will occur. The clouds /and higher
dewpoints /in the 20s/ will help to curb the temperature drop
tonight...and mins early Friday will be several degree f or more
higher than early this Thursday morning.

The uncertainty of the amount of cloud cover tonight and early
Friday...combined with the increasing surface dewpoints...and light
southeast winds has directed US toward transitioning from a freeze watch
to a frost advisory...with min temperatures in the 32-35 range in most
locations.

Some of the typically colder rural valleys could see
daybreak temperatures in the upper 20s /esp if a period of clearing
occurs/. Temperatures across the central and northwest zones will be just a tad
lower than those lower susq counties covered by the frost
advisory.

&&

Short term /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
Friday night.

&&

Long term /Friday night through Wednesday/...
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
underway.

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 /19z Thursday 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 /during the middle to late afternoon across the lower susq valley
airfield/...and reaching the central mountains late tonight/early
Friday 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 during the early evening.

Chance for light rain to impact mainly northwest late Friday afternoon or
Friday night with low probability of restrictions. VFR elsewhere.

Outlook...
Friday...generally VFR. Areas of MVFR ceilings poss across central and southeast
PA early.

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.

&&

Ctp watches/warnings/advisories...
frost advisory from 2 am to 8 am EDT Friday for paz057-059-
063>066.

&&

$$
Synopsis...Lambert
near term...Lambert
short term...dangelo/Lambert
long term...steinbugl
aviation...Lambert