Scientific Forecaster Discussion
fxus61 kctp 121122
Area forecast discussion
National Weather Service State College PA
622 am EST Thu Dec 12 2019
high pressure will be right over the state this morning and
slide to the east through the day. A complex storm system will
move northward from the southern states, arriving Friday and
last into Saturday. While a brief period of mixed precipitation
is possible on early on Friday, it will turn milder and most of
the precipitation will fall in the form of rain. High pressure
then moves in for Sunday before another storm approaches on
Monday or Tuesday.
Near term /until 6 PM this evening/...
last few flurries slipping south just to the east of the office.
There must be super-efficient Crystal-production in the clouds
since the clouds barely cover the area of returns on the radar.
Few other clouds over the County Warning Area attm and those are being squashed
by the lowering inversion. Dewpoints already into the single
digits. These should continue to drop a bit thru the morning.
Mostly sunny should be okay until mid aftn when some higher
clouds slide overhead from the west topping the 1038+mb ridge.
Temps are pretty cold this morning, but will rise as best they
can with the mixing heights only up to about 925mb, and temps
there -5 to -10c. Maxes will only get into the u20s north and m30s
S, colder on the ridges all over.
Short term /6 PM this evening through Friday night/...
interesting and challenging system moving in from the south -
and a little from the east - later tonight and Friday. Temps
should cool off into the M-u20s at first tonight. Then there is
a llvl easterly flow develop into the sern counties and
Poconos with the cold air damming showing up nicely. This
easterly flow brings with it some moisture trapped under the
inversion. The href members and NAM are most bullish on the
patchy quantitative precipitation forecast in the east before any more- widespread rain would
arrive later in the day. This could lead to some patches of
dz/fzdz in the east, esp on the ridges before sunrise. Quantitative precipitation forecast thru
15z would be very light (just a couple of hundreths at most)
there. So, there is the possibility for a little bit of ice to
form on things. But, this 00z guidance seems to be the first
widespread indication of this occurring. A leveling-off or even
a bit of a rise to temps may occur later tonight with mins just
5-6f lower than the maxes from today.
Sub-freezing air takes a while to shrink from the outside in on
Friday during the day. Thanks, topography and high pressure to
The arrival of better forcing is later in the day, or even not
until closer to midnight Fri night. Rain may be rather patchy on
Friday, with no sig quantitative precipitation forecast until after sunset. So, while there is
still a threat of temps staying below freezing on the ridge tops
of the central and western mountains, I am still not confident
enough to Post an advy at this point. Collaboration with
neighboring offices resulted in similar thoughts from them.
The main rain will be Fri night and Sat as the sfc low GOES
right overhead. It should be mild enough after sunset to keep it
Long term /Saturday through Wednesday/...
*heavy rain possible (1-2 inches) in east-central PA Friday
night into Saturday
*period of snow/mixed precipitation likely later Monday into
tuesday; potential for winter weather should be monitored
Low pressure system will draw deep moisture/above normal precipitable water
northward into the area Friday night resulting in widespread
moderate to briefly heavy rainfall. Storm total rainfall of 1
to 1.5 inches is forecast across east-central PA. Will need to
watch for a transition back to snow on the backside of the
system as the upper low pivots into the northeast and gusty
northwest flow Ushers cold air back into the region. Lake effect
snow accumulation is likely in the favored upslope high terrain
and snowbelts Sat night into Sunday. Temperatures trend colder
Saturday to Monday as the active pattern briefly takes a pause.
Winter weather threat will need to be monitored for early next
week with the potential for snow and ice to impact the area
later Monday into Tuesday. Updated local winter storm outlook
graphics on the web and severe weather potential statement to reflect the latest trends/probs.
Below average temps are forecast into the second half of next
Aviation /12z Thursday through Monday/...
high pressure building into the region will ensure VFR
conditions and light wind through this evening.
Fri...rain/low cigs likely, especially late.
Sat...rain/low cigs likely, especially early. Windy late.
Sun...gusty west wind. Am low cigs/snow showers possible west mtns.
Mon...PM low cigs/wintry mix possible.