Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1100 PM EST Thursday Jan 29 2015
an Alberta clipper/Arctic cold front will cross the area tonight.
High pressure will return for late Friday into Saturday. A new
storm is expected to pass well south of the area later Sunday
into Monday...followed by another surge of cold air for early
Near term /until 6 am Friday morning/...
regional radar loop shows steady snow associated with ll jet/warm air advection
pushing east of central PA at 00z. However...potent looking
shortwave in water vapor loop is supporting another batch of
precipitation over western PA at 00z...which will swing through the County Warning Area between
00z-06z. For most of central PA...expect occasional light snow to
continue through late evening...as middle level shortwave rolls through. Over
the S tier counties...latest hrrr and 4km NAM soundings continue
to indicate enough warming aloft for some light freezing rain
Have decided to cover the threat for icy conditions with a
Winter Weather Advisory over my southern tier. Overall reasoning
has not changed with just enough warm air aloft expected to cause
a period of nuisance-type icing.
Have tweaked snowfall totals in our gridded forecasts...based on
surface reports and latest guidance. Looks like around 4 inches across
the northwest mountains...to less than an inch from Harrisburg southward. Have
included light ice totals of a tenth of an inch or less across
The cold front should be swinging through the Allegheny Mountains around
03z and the eastern zones shortly after 06z. Behind the front...only
scattered lake effect snow showers should remain early Friday morning
over the Allegheny Mountains
Low temperatures tonight will range from the upper teens across the western
mountains...to the middle and upper 20s across the susq valley.
Short term /6 am Friday morning through 6 PM Friday/...
Friday will be a blustery and cold day as Arctic air pays a
return visit. Lingering snow showers will favor the usual western
and northern higher terrain with central and eastern areas
probably seeing little more than some stray flurries.
Temperatures will likely peak early and either stay steady or fall
throughout the day. Wind chills will range from 5 to 15 below zero
over western higher elevations by late in the day as winds become
gusty behind the departing front.
Long term /Friday night through Thursday/...
took out mention of snow Friday night...flow too northerly.
Wind chill advisories will likely be needed across north
central PA Friday night into Saturday morning until around
14z. Still mainly 3rd period...will hold off an advisory
Saturday looks sunny but on the cold side.
Some chance of some light snow Saturday night and early Sunday
across the far north...with cold front dropping southeast. Have
low chance in early Sunday across the far west.
Models still show potential for a low moving just south
of PA later Sunday into early Monday. Thus left snow in
the forecast. Did some make a few adjustments. Main thing was
to cut back probability of precipitation across the northwest early Monday. Not seeing
a lot of potential for lake effect late Monday...flow too
northerly. Thus made a few adjustments Monday night.
Another shot of cold air in for Monday night into Tuesday...as
high pressure builds in from the plains.
Models hint at another low tracking near the area on Wednesday.
Have low end probability of precipitation for snow. More cold air behind that system.
Aviation /03z Friday through Tuesday/...
main area of snow asscd with a clipper system...but ahead of the
cold front to pass later tonight...has moved east of central PA.
Secondary area of mainly light snow now working east across the
region. Observed conds line up line typical Post frontal
flow...with IFR in the northern and western mountains...MVFR in the central mountains
and VFR over the southeast/middle and lower susq valley.
Reduced conditions should improve overnight with the passage of
the cold front...around 06z Friday over the west. More like
08-11z over the southeastern areas. The conditions at bfd and jst will
likely remain MVFR/IFR with snow showers into Friday.
Sun...lower conditions possible over southern areas associated
with a storm moving through the Carolinas.
Monday...reduced conds early in snow showers. Improving from west to
east afternoon Onward.
Tuesday...no sig weather.
Winter Weather Advisory until 7 am EST Friday for paz004>006-
Winter Weather Advisory until 1 am EST Friday for paz025>028-
short term...Fitzgerald/la corte