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FXUS61 KCTP 232148
Area Forecast Discussion
National Weather Service State College PA
448 PM EST Mon Jan 23 2017
A strengthening storm will move east of the NJ coast tonight
and early Tuesday. High pressure and unseasonably mild
conditions will briefly return for midweek before a pattern
change brings colder temperatures and lake effect snow to close
out the month.
* Major cyclone to affect the region through tonight
* Elevation dependent snow storm likely
* Several inches of heavy wet snow not out of the question even
  throughout the Central Valley areas
* Strong easterly LLJ 50-65kt/5-7 sigma...translating to wind
  gusts of 35 to 45 mph near and to the east of the Susquehanna
* High probability of at least 1" QPF over much of central PA
* Explosive dynamic cooling leads to steep mid level lapse rates
  and a few instances of thunder snow across the region late
  today and tonight
The deep storm that has been responsible for several rounds of
severe storms and deadly tornadoes over Dixie the past several
days, is now located near Norfolk, VA and will take a track
to the northeast up along or just off the NJ coast tonight.
Increasing upper diffluence and mid-level frontogenesis across
the Mid Atlantic Region will lead to bands of moderate to
briefly heavy precip pushing NWWD, then consolidating on a
roughly NE/SW axis near the front range of the Alleghenies from
near KFIG and KAOO and KIDI late today
through at least the first half of tonight as the channel
anomalously high PWAT air and low-level easterly winds pivots
around the north side of the approaching, negative tilt Upper
Multi-model and EFS Vertical Thermal Profiles are very close to
supporting various types of various locations as
dynamic cooling lowers temps at all layers just below freezing
over the Laurel Highlands first late today, then across central
and NEPA where varying thickness of the slightly above freezing
layer of marine air off the Atlantic will be found.
We maintained the basic timing and configuration of the
previously posted Winter Storm Warning and Advisories for NCENT
PA, but issued a Winter Weather Advisory for the Laurels for
late this afternoon through midnight where 2-5 inches is
expected in the valleys there, with higher amounts of around 6
inches on the ridge tops AOA 2200 FT MSL.
17-20Z runs of the HRRR shows the first batch of moderate to
heavy QPF, in the form of Rain to Sleet, with Laurel Highlands
(and shortly afterward the Central PA valley locations) seeing
Big, Gloppy Wet Snowflakes.
This enhanced area of QPF will be lifting gradually north
across the CWA between 21-03Z and becoming concentrated across
the northern tier counties of PA later tonight.
Elevated...slantwise instability coupled with steepening mid/upr
lapse rates moving in from the south should lead to some
isolated TSSN (or TS some precip type) through at least early
A second surge of mid/upper level energy pushes NWWD over much
of central and eastern PA after midnight and lingers through
daybreak in the form of an "elongating" area of "Wraparound"
snow/sleet. The main change for later this evening may be the
need to extend the Winter Weather Advisory to fill in some of
the Central Susq Valley and Central Mtn zones for up to several
inches of Wet Snow.
Temperatures in most locations of Central and Northern PA will
be nearly steady or slowly falling from the mid and upper 30s
late today, The rain will mix with, then change to sleet and wet
snow during the mid to late afternoon across the higher terrain
of central and western PA where temps will be between 32 and
A gradual changeover to sleet and wet snow of varying intensity
will occur throughout the central valleys and northern mountains
between 5 and 7 pm.
PTYPE will be mainly rain across the Lower Susq Valley through
the first half of tonight, then a rain/wet snow mix with up to a
slushy 1 to 2 inches on the ridges around and to the north of
the Greater Harrisburg Area.
The snow should begin to taper off to scattered snow showers
after midnight across the Laurel highlands but continue in most
other areas.
Ongoing winter storm overnight for Central PA, with biggest impacts
shifting to the NE portion of CWA.  Best dynamic cooling and highest
QPF impacts areas north of I-80 from mid evening onward, though a
band may extend from KIPT SW back toward KUNV/KAOO that may produce
a couple of inches of wet snow if it gets intense enough. Transition
to snow should be complete by mid/late evening in the NE, and high
precip rates should produce a couple hours of snowfall rates of 2"
per hour - so warning area still looks good. Precip looks to become
light over the SW this evening with any significant snows ending
with a general light snow persisting much of the overnight.
Primarily a rain/snow mix late in the SE.
Winter storm impacts over North-Central/Northeast PA will come
to an end by Tuesday afternoon as strong surface low continues
to lift northeast along the Mid Atlantic/New England Coast.
Strong WAA pattern quickly follows into mid week with high
pressure ridge axis crossing the area on Wednesday. Maximum
temperatures on Wednesday are fcst to climb well-above normal
for late January.
A well-advertised pattern change remains on track from the
second half of the week into the weekend, with high confidence
in a long wave trough carving out over the Eastern U.S. This
will result in a prolonged period of seasonably cold temperatures
and lake effect/high-terrain snow showers during the remainder
of the period. Several inches of snow is probable in the typical
locations like the Lake Erie Snowbelt.
A storm moving off the Carolina coast today will redevelop along the
coast and moving up just east of NJ tonight and early Tuesday.
Breezy across the SE today with strong easterly 850mb flow producing
gusts in the 30s at KLNS. These will gradually subside through early
A gloomy day for Central PA ongoing as large area of rain and low
clouds bringing cig/vsby restrictions to the region. Heaviest precip
through 00z will be across the south and central.  With atmosphere
cooling, precip type will switch over to a wintry mix/snow in the
Laurel Highlands /KJST/ late this afternoon and begin to mix with
sleet or snow mainly in higher elevations elsewhere through 00z.
Even enough instability to mention possibility of an isolated
bolt of lightning here or there, but chance definitely too low
for mention in terminals (except for a very short-range direct
Cooling continues this evening, with a transition to primarily snow
mainly north of I-80, but edging back toward KUNV as well. Central
Mountains will likely see a mix of rain/snow with the SE remaining
primarily rain. Restrictions will continue, with conditions slipping
to IFR just about everywhere.
Improvement on Tuesday as storm lifts to the NE and precip comes to
an end. Improvement arrives first over the SE half of CWA, though
MVFR likely continues through the day.
Tue...Rain/snow ending in the morning. Widespread sub-VFR will
improve for SE half by aftn.
Wed...Low cigs/rain possible western 1/2. Breezy late.
Thu-Fri...MVFR/IFR in rain/snow showers west. MVFR to VFR east.
Winter Weather Advisory until 7 AM EST Tuesday for PAZ005-
Winter Storm Warning until 10 AM EST Tuesday for PAZ006-037-
Winter Weather Advisory until midnight EST tonight for PAZ024-
NEAR TERM...DeVoir/La Corte/Lambert
LONG TERM...Steinbugl

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