Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service State College PA
220 am EDT Friday Apr 18 2014

Synopsis...
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 today/...
some low clouds moved across the southern areas and appeared to
hamper the frost advisory but we have had some clearing as this
feature moved west and now have reports of temperatures in the
34-37f range though bigger cities still near 40. So will keep
frost advisory in effect as some locations now below the magic 36f
shelter height. Winds have luft a bit too.

Most of west is clear and temperatures running warmer than last
night. Really massive 1040 hpa high over New England with +3 sigma
pressure anomalies has kept cold air in at low levels but now
bringing some marine layer air into southeast.

Satellite imagery shows the system to our west which will try to
move into this large anticyclone. Sref shows some chance probability of precipitation as
the anemic front pushes into PA later today and this evening. Kept
probability of precipitation in northern tier and used 3-hour sref probability distribution
function "pops" to show progressive evolution. I lowered the
values as these are not statistical probability of precipitation as in MOS but a
distribution function in a system with a low quantitative precipitation forecast wet bias.

Hard to get excited about a trough that has positive pressure
anomalies!

Any rain would be light and the anticyclone behing this
system at 1030 hpa is a bit weaker. Its a good time for
anticyclones.

&&

Short term /tonight through 6 PM Saturday/...
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 /Saturday 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
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 /06z Friday through Tuesday/...
a layer of shallow/broken MVFR-low end VFR stratocu will be sliding
into susq valley airfields from the southeast overnight...and ultimately
edging into portions of the central mountains just before sunrise.

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.

During the day on Friday...chance for light rain to impact mainly northwest
late in the afternoon into the evening with low probability of restrictions.
VFR elsewhere. Light southeast winds will shift to the south and
then SW through the day...with increases to 5-10 kts with gusts to
around 15 kts.

Outlook...
tonight-Sat...reduced ceilings/visibilities poss with chance of light rain
showers mainly northwest half. VFR elsewhere.

Sun-Mon...no sig weather.

Tuesday...several-hour period of MVFR ceilings poss with brief MVFR visibilities
in showers accompanying a cold frontal passage.

&&

Ctp watches/warnings/advisories...
frost advisory until 8 am EDT this morning for paz057-059-
063>066.

&&

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