Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
252 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/...
have decided to cover the threat for icy conditions into the
evening hours with a 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.
The main area of precipitation is on track and shown by the hrrr to be
entering my western zones by 18-19z. Still some concern for a
brief period of light freezing rain or sleet so we put an
advisory over the southern counties to cover the potential for
some light icing. Guidance is consistent in showing warm air
surging in aloft today...then being pinched off quickly as precipitation
develops and the column evaporatively cools. However...the
rap/hrrr hourly data show the warm air actually pushing back north
between 21-00z over the southwestern zones...complicating the precipitation type
scenario from The Laurels eastward along the Maryland border
A strong shot of warm air advection aloft and moderately strong upper level
divergence associated with the right entrance region of an upper
level jet maximum across southern Ontario will lead to periods of snow
this afternoon into tonight. Already 4-Star snow at Meadville
with moderate snow over northestern Ohio up into Erie.
Snowfall totals in our gridded forecasts look reasonable and we
have included light ice totals of a tenth of an inch or less.
The cold front will be entering western PA just after dark...and
should be swinging through my eastern zones between midnight and
6 am. Snow will taper to snow showers and flurries by late
tonight...mainly in the isolated form across the central and
Low temperatures tonight will range from the middle to upper teens across
the western mountains...to the middle and upper 20s across the susq valley. If
the front is faster than expected...these could be a tad too high.
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 Wednesday/...
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 /20z Thursday through Tuesday/...
VFR conditions will rapidly deteriorate as snow overspreads the
region from west to east.
Snow will begin shortly in Bradford. Expect IFR conditions to
develop rapidly with the snow...spreading east 18-00z. Southern
tier terminals from jst-aoo east into the lower susq valley could
see a period of light freezing rain or sleet as the precipitation
Reduced conditions should improve overnight with the passage of
the cold front...around 03z Friday over the west. More like
06-09z 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-
near term...la corte
short term...la corte