Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
521 PM EST Wednesday Dec 11 2013
a cold cyclonic flow over the Great Lakes will maintain below
normal temperatures through the end of the week...with lake
effect snows focused over far northwest Pennsylvania in the
perennial snowbelt region. A pair of weak clipper systems passing
to the north will reinforce the cold air. For most of the area...the
next few days will be cold and dry. The active early season winter
pattern looks to resume with another storm system likely impacting
the area Saturday into Saturday night...followed by more cold and
brisk conditions into early next week.
Near term /until 6 am Thursday morning/...
Sat imagery shows weak/moisture limited upper trough moving east
across Lake Erie into western PA. Passage of this trough should
serve to restructure wind flow to enhance le snow shower activity
across northwestern counties into Thursday morning as well as increase
coverage of clouds and isolated snow showers across the northern and
western mountains otherwise little widespread significant weather should
accompany this trough/shortwave given the limited moisture.
Les advisory remains in effect for Warren Colorado.
Short term /6 am Thursday morning through Friday night/...
a series of northern stream impulses are forecast to race eastward across the Great
Lakes around the base of large polar vortex over Hudson Bay. The
vortex should gradually shift to the north and east by the end of
the period and allow for at least modest 500mb height rises and
slightly moderating temperatures as the 1000-500dm thicknesses gradually
increase. There is some uncertainty focused on the upstream side
of the trough with placement diffs over Ontario...which appears to
impact the low-level temperature gradient and magnitude of high pressure cell
moving over Montreal Canada by 12z Sat. This feature looks to play
a role in another winter mixed precipitation event into the weekend.
In general...expect the lake effect snow mechanism to fade into
day 3 with the focus shifting to developing low pressure/inverted
trough over the Tennessee Valley and associated warm air advection/overrunning precipitation possibly
reaching the area by early Saturday morning. Day 2/Thursday looks like
the coldest day based on consensus guidance with highs 20 degrees
below normal. Wind chills will remain a concern and will continue
to highlight in the severe weather potential statement. Sub-zero apparent temperatures seem likely during
the nighttime and early morning hours across the west-central mountains
Long term /Saturday through Wednesday/...
the active early/cold-season pattern across the eastern Continental U.S. Will
resume this weekend...likely bring more winter weather to the area
from Saturday into early Sunday. A consensus of model data and
their respective ensemble means show the most likely outcome
being a Transfer of surface low pressure from the Ohio Valley to the
middle Atlantic coast by Saturday night...with subsequent deepening
of the coastal low as an Arctic vortex plunges into the Great
Lakes on Sunday. The far southeast could go over to a cold rain around
Did not change a lot on the package. System is similar to what
we had last Sunday. Expect some light snow on Saturday...mixing
with some sleet and very light freezing rain/drizzle across
southern PA Saturday after into Saturday night.
By 12z Sunday...cold advection will set in...as the coastal
Not seeing a lot of support for a real intense snow band
near the Maryland border as was the case on Sunday. Overall expect
most areas to see 1 to 3 inches...perhaps 4 to 5 inches in a few
A cold and blustery west-northwest flow should follow behind the departing
coastal low with lake effect/upslope snows over the northwest mountains and
western high terrain later Sunday into Sunday night. High pressure should
arrive by early next week. Temperatures should moderate into Tuesday/Wednesday as
flow veers to the west/SW ahead of a clipper wave dropping across the
northern Great Lakes. Large scale height falls associated with another polar
shortwave spreading across the Great Lakes/mid-Atlc may spin-up another
low off the coast...but at this point its latitude would be too
far north to impact the local area.
Aviation /22z Wednesday through Monday/...
VFR will continue over most of the region through the evening
and overnight...except for bfd where IFR conditions with frequent
snow showers will dominate. Jst could also see brief reductions as
upslope flow brings clouds and some snow showers.
A weak cold front will move across the region tonight reinforcing
the cold flow over the lakes and the lake effect snows that will
continue over the northwest and parts of The Laurels.
On Thursday...high pressure will build over the Tennessee Valley and southern
Appalachians bringing widespread VFR conditions to the region once
again. Though bfd could linger with reduced conditions due to
lake enhanced clouds/snow showers into Thursday afternoon.
Friday...no widespread sig weather.
Sat-sun...snow or mixed precipitation with low ceilings/visibilities possible.
Monday...mainly VFR. Perhaps a few snow showers near the New York
lake effect Snow Advisory until 7 am EST Thursday for paz004.