Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
300 PM EST Monday Dec 9 2013
a strong jet stream resides to the north of the area . It will
provide forcing to generate an area of snow over the Appalachian
Mountains tonight. That snow will move across the southern half of
the state during the morning and early afternoon. Cold west to
northwest winds will bring colder air in through the rest of the
week. Scattered snow showers are also expected in the
northwestern parts of the state for the rest of the week. But it
will be generally dry and cold elsewhere. The weekend looks like
it will hold the next high chance of widespread precipitation.
Near term /until 2 am Tuesday morning/...
big breaks in the clouds appearing this afternoon and should
become more prevalent through the evening. A few flurries/rain
drops may be found in the western Highlands through the evening...but
drying found elsewhere.
Short term /2 am Tuesday morning through 6 PM Tuesday/...
snow pack widespread over the area...and 800 mb temperatures will also fall
a few degrees. However...the wind will remain up around 10kts all
night - a little slower in the valleys and faster on the ridges.
This should result in min temperatures in the upper teens in the north
and M-u20s in the southeast. Rapid development in precipitation will be
occurring over the Tennessee Valley early tonight as a very fast jet
streak will pull lots of moisture northeast from the Gulf of
Mexico. The lack of negative tilt to the trough behind the jet and lack
of easterly flow will speall a quick event for late tonight and
Tuesday. The latest model runs seem to be too wet with the forecast vs
earlier guidance and with wpc guidance. Have posted a Winter Weather Advisory
for the southern half of the area as quantitative precipitation forecast on the of 0.25-0.35 inches and
a 15:1 ratio on average will produce advisory range snows for most of
the region south of State College and Williamsport. No worries for
mix precipitation with this event. Profiles are all cold and snow ratios
north of rte 22 may be 20:1 or higher. The snow should taper off
through the late morning and early afternoon. The westerly flow
will keep some shsn in the forecast for the western mts...especially Warren
Colorado...for the afternoon and into the next period.
Long term /Tuesday night through Monday/...
as the aforementioned system pulls east Tuesday night and Wednesday...
Arctic air surges into the region for the rest of the work week.
Northwest flow aloft and around building high pressure at the
surface will bring lows in the single digits and teens for Thursday and
Friday morning...and highs mainly in the 20s.
This weekend...flow turns westerly bringing gradual moderation to
temperatures. Another wave of low pressure prognosticated for later Sat
into Sunday with light precipitation possible.
Aviation /20z Monday through Saturday/...
low ceilings and patchy fog/drizzle persisting this afternoon across
central PA...with widespread IFR conds. Could see a bit of
improvement late in the day across the east...as a weak
downsloping west wind develops. The west wind and upsloping conds
will not do much to help jst or bfd...where low ceilings and scattered
-shsn are expected to persist into tonight.
Another round of wintry weather...in the form of steady light
snow...will overspread central PA late tonight into Tuesday am.
Expect ceilings/visibilities to drop once again as the snow develops. This
will be a quick-moving system...and the snow should begin
tapering by afternoon.
The middle to later portion of the week will be dominated by cold
west/northwest flow. This means reduced ceilings/visibilities will persist
at jst and bfd in lake-effect/orographic clouds and -shsn...with
generally VFR conds dominating farther east.
Tuesday...light snow and reduced cigs/vsbys.
Wed-Thu...-shsn and reduced ceilings/visibilities possible across the west.
Friday...no sig weather expected.
Sat...low pressure could bring another round of wintry precipitation...with
Winter Weather Advisory from 3 am to 4 PM EST Tuesday for