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NWS State College, PA Forecast Discussion


000
FXUS61 KCTP 120347
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1047 PM EST Tue Dec 11 2018

.SYNOPSIS...
Seasonably cold temperatures will continue through midweek. A
dusting of snow is likely overnight in the northwest snowbelt
and Allegheny ridge tops. A more widespread light snow of an
inch or two is likely Wednesday night and Thursday morning over
a wider area. Milder air will return to central PA for late in
the week with rain to start the weekend.

&&

.NEAR TERM /UNTIL 8 AM WEDNESDAY MORNING/...
Low clouds cover almost 100pct of the area, now. Only a few
slots of clear are left due to lee wave action and downsloping.
A little snow/flurries falling at IPT and here in HapVal. But,
there is not much forcing left. Therefore, we will hold onto the
gradual decrease in PoPs for the area overnight. Temps did rise
a little as the clouds arrived, but will probably drop a deg or
two thru the rest of the night, esp in the SE where some/more
breaks will show up later tonight.

Prev...
So much for clear skies. Stratus has returned on the WNW flow
just aloft. The gusty wind over the higher elevations has
materialized, and should be gusty for the next several hours.
Have refined the timing of the snow arrival as the snow seems
to be just about 2 hours behind the front edge of the clouds.
The air is much drier over the srn 2/3rds of the area, though.
So, I do expect the advance of the snow to slow and stop as the
moisture aloft gets thinner and farther from the sfc. Cloud
bases are barely below 1000ft over the far nrn tier, and jump to
>2000ft before you get as far south as St Marys and Wellsboro
airports. The qpf is almost nil, and accums will be just a
dusting to an inch along and N of Rte 6. Perhaps the rest of
the area N of I-80 and W of I-99 might see a dusting as well.
But, the time of best lift is very brief and little snow should
be left after 3 AM. Will mention flurries for much of the area.

Prev...
Widespread sunshine and a freshening west to southwesterly flow
has helped temps to rebound to the mid and upper 20s across the
NW mtns and near 40F in the Metro Areas of the SE.

Compact upper short wave and a relatively dry cfropa will drop
SE from the GLAKES tonight in association with a potent 105KT
upper jet. This feature aloft will slice right through the SW
half of the CWA and create a sharp gradient in POPs for light
snow showers and perhaps more impactfully - a 4-6 hour period of
gusty NW winds between 35 and 40 mph across the Laurels beneath
the thermally indirect right front quad of the jet. So we have
likely POPs for mainly a coating to possibly one inch of snow
across the NW mtns tonight with little more than some flurries
across the Central Ridge and Valley Region of the state and
communities throughout Susq Valley.

Some clouds (mainly later tonight across the SE zones) and at
least light west to NW breeze around the time of...and in the
wake of the CFROPA will mean somewhat higher low temps than we
experienced this Tuesday morning. However, mins will still 3-6F
below normal across the Susq Valley, and close to normal
elsewhere.

&&

.SHORT TERM /8 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
Narrow ridge of high pressure briefly visits the area early
Wednesday, bringing an end to any lingering snow showers or
flurries by midday. Another seasonably cold and mainly dry
period during the day Wednesday with max temps 30s still about
5 degrees below average.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
A compact/closed H5 low is projected to weaken as it tracks
eastward from the Great Lakes/Ohio Valley into the northern Mid
Atlantic Wednesday night into Thursday.

Model consensus QPF continues to suggest a several hour period
of WAA light snow is probable especially over parts of the
northwest Alleghenies/higher elevations and could result in a
larger coverage of light snow accums (one half inch to 2 inches)
by late morning/midday Thursday.

This should be just enough for some slippery travel Thursday
morning. Confidence (and precip probs) have increased further
from the previous early morning fcst package, but still not
quite a slam dunk given the slightly weakening system and diffs
in the light model QPFs averaging between several hundredths and
0.15 of an inch. Light snow may linger into Thursday afternoon
before diminishing/shifting southeast Thursday night. Some
freezing drizzle is possible late Thur/Thu night as we lose the
layered seeder-feeder mid and upper level clouds.

Storm system over the southern U.S. will spread milder air and
rain into the area by the start of the weekend. Model trends
indicate a slower arrival to rain with the most likely wettest
period Friday night into early Saturday. There is the potential
for heavy rain with a strong southerly LLJ and above normal PWs.
Confidence remains low concerning rainfall amounts and flooding
risk - something to monitor in the coming days. Also need to
watch the thermal profiles at the onset for possible mixed pcpn
although it looks like mostly a rain event at this point.

There are some big model differences (GFS/EC) in how the system
evolves heading into next week. This would have significant
implications on the fcst. It appears to be due to phasing
issues with the GFS merging the northern+southern stream energy.
The 12Z GFS brings the low quickly through and the EC brings a
more suppressed system slowly bringing the low off the NC coast
and overall warmer solution in the wake of the system. Very low
confidence at by the Sun-Mon timeframe given the wide model
spread and growing uncertainty.

&&

.AVIATION /04Z WEDNESDAY THROUGH SUNDAY/...
Minor changes made to the 03Z TAF update.

Earlier discussion below.

00Z TAFS sent.

Weak cold front will spread some snow showers across the area
later tonight and early Wednesday morning, mainly across the
north and west. Conditions will become VFR again by late
Wednesday morning or early aft.

Near and just behind the cold front tonight, a gusty west to NW
wind will be across at least the Central, NW MTNS and Laurels.
Prevailing wind speeds should average 10-15kts with gusts into
the mid and upper 20s. Gusts of 30-34KT possible INVOF KJST and
perhaps KAOO for a several hour period later this evening
through about 07-09Z Wednesday, then decreasing wind that will
veer all the way around to a light east to SE speed and
direction Wed aft.

.Outlook...

Wed...Early AM low cigs possible W Mtns. Evening light snow
possible western half of Pa.

Thu...Low cigs possible, mainly central mountains.

Fri...Rain/low cigs possible, especially late.

Sat...Rain/low cigs possible.

Sun...Clearing.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...Dangelo/Lambert
NEAR TERM...Dangelo/Lambert
SHORT TERM...Lambert
LONG TERM...Ceru/Steinbugl
AVIATION...Martin

NWS CTP Office Area Forecast Discussion

Courtesy of the National Weather Service forecast office State College, Pennsylvania




Fast Weather Facts and Folklore

AMAZING WEATHER FACT - Both the driest year on record (2001) and the wettest year on record (2005) for the state of Maine occurred within five years of each other.