Area Forecast Discussion
Issued by NWS State College, PA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 060720
Area Forecast Discussion
National Weather Service State College PA
220 AM EST Tue Dec 6 2016
A storm system will move in from the Gulf Coast states and affect
the region Tuesday into Tuesday night. Much colder air will move
in after a cold front passes on Wednesday. The end of the week
will feature a prolonged bout of lake effect snow and much-below
.NEAR TERM /UNTIL 6 AM THIS MORNING/...
The overnight will be fair and dry under increasing mid and high
cloudiness. Lows will drop back in the mid 20s to low 30s across
.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
A low pressure system with some moderate upper level forcing will
be moving into the region tomorrow morning. The high pressure
bubble that will be over the region today will move quickly to the
northeast. A low will move into the OH valley late Tuesday with
the earliest bands of precipitation from this storm reaching
southwest PA by Tuesday morning. The most difficult part of the
forecast is the p-type. The latest NAM brings in precipitation
between 12Z to 15Z with some warm air advection aloft. However
evaporative cooling should take the warm air advection quickly
down to the wet bulb which should switch the precipitation type to
snow. So there remains the threat of freezing rain/sleet through
the Laurels with generally a wet snow/rain event through the rest
of the region. There is still a slight chance for some mixed
precipitation through the Lower susquehanna but given marginal
temperatures and quickly cooling mid levels have left the area out
of the advisory for now.
Have the advisory with freezing rain for the Laurels but as the
region warms during the daytime a rain/snow mix will intrude and
switch to snow as the day continues.
Since any snow falling will be fairly wet, accumulations are
tricky. The Central mountain temperatures and through the
northeast should be cold enough for a couple inches to be
probable. At this time, we will keep the 12-24 hr forecast snow
amounts around 1-2" with the highest amounts over the NC mtns. So
tomorrow will be fairly wet with slippery roads.
.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
The long term period will begin with the rather quick ENE departure
of the synoptic wintry precip event. Wet bulb/thermal profiles the
first half of Tuesday night area just cold enough for mainly snow
across much of central and northern PA with light additional
accumulations of snow sleet (and patchy -FZRA across the Laurels) as
the brunt of the stronger southerly Warm advection and UVVEL will be
racing off to the northeast with adiabatic and evaporational cooling
being overcome by the weakening warm advection bringing the sfc to
925 mb temps to around or just above Zero C in the 06-12Z period
Expect some lingering -SHSN/-SHRA Wednesday morning along and just
in the wake of the CFA (within a period of mdtly strong, 925-850 mb
cold advection and westerly upslope flow across the Alleghenies).
High Pressure and drying noses in from the west Wednesday afternoon
and night with partial clearing across the central ridge and
valley region and beneath a fast WSW flow aloft. Temps Wednesday
through Thursday will be near to slightly below normal.
Broad and weak to moderate large scale lift/low to mid
level warm advection develops late Wednesday night across the
mtns of Wrn PA, and spreads across the remainder of Central PA
Thursday ahead of an approaching arctic front and beneath the
thermally direct segment of a 150kt 300mb jet moving by just to
The subsidence inversion base lifts rapidly up to 7-10 kft agl
Thursday afternoon, right through Friday night. The mean wind in the
925-850mb layer veers from about 270 deg to 295-310 deg Friday and
Friday night creating the likelihood of a significant/heavy Lake
Effect/orographic snow event for the NW mtns (i.e. mainly the
snowbelt of NW Warren county), and in a few preferred locations
across the Laurel Highlands.
Gusty NW winds could top 40 mph at times Friday.
The large area of High Pressure and modified arctic airmass will
slide off the east coast Sat night and Sunday. The coldest temps of
the season so far will occur Sat night/early Sunday with lows in the
lower to mid teens across the snow covered ground of the NW/Ncent
mtns...and upper teens to l20s elsewhere.
a chance of some like snow/snow showers returns with a warm front
Sunday night/Monday. The boundary layer could become warm enough by
Monday night to mix in rain showers. especially throughout the
central and southern valleys.
.AVIATION /07Z TUESDAY THROUGH SATURDAY/...
MVFR cigs over the northwest airspace should trend to VFR over
the next several hours. Elsewhere expect VFR with increasing/thickening
high clouds. Cigs will lower from south to north later this
morning with precip spreading over the airspace by the afternoon.
P-types should transition from frozen/freezing to rain/drizzle
across the western 2/3 of the airspace into Tuesday night. The
southeast airspace should see mostly rain with some sleet possible
at the onset. Confidence in ptypes is marginal given complex and
evolving thermal structure/evaporative cooling in the boundary
layer. Elevation and pcpn rates will also be a factor. A period of
LLWS is possible at BFD/JST from roughly 6/18z-7/03z. Overall,
expect flying conditions to deteriorate with high confidence in
sub-VFR Tuesday afternoon into Tuesday night.
Wed...A.M. low cigs becoming mainly VFR.
Thu-Fri...Becoming windy with periods of snow showers. Mainly
MVFR/IFR west to MVFR/VFR east.
Sat...Decreasing winds. Low cigs/-SHSN psbl NW. VFR east.
Winter Weather Advisory from 6 AM this morning to midnight EST
tonight for PAZ024-033.