Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
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FXUS61 KCTP 221127
Area Forecast Discussion
National Weather Service State College PA
627 AM EST Sun Jan 22 2017
A storm moving through Dixie today will move off the Mid
Atlantic coast Monday to near Long Island Tuesday. High pressure
and mild conditions will briefly return for midweek before a
pattern change brings more seasonable temperatures to close out
.NEAR TERM /THROUGH TONIGHT/...
We extended the fog advisory to cover the late burn off times
that tend to be most likely this time of year.
Otherwise another bland mainly cloudy day is in store for most
of the region with temperatures that are very mild for the
traditionally coldest days of winter. Models want to increase
the chances of some light rain advancing into my southern zones
the deeper into the day we get. I have relatively high Pops but
only light amounts of rain.
Near term guidance is in good agreement with tracking the upper
low out of the southern Miss Valley to NC by sunrise Monday.
Moisture will continue to increase ahead of the system and it
seems a good bet that most if not all parts of the forecast area
will be wet by morning.
.SHORT TERM /MONDAY/...
* Surface low taking a very favorable track for winter storm.
* Monster easterly jet 60-75 kts forecast.
* Number of SREF/GEFS plumes showing snow is on the increase.
* Dynamic cooling under intense forcing will bring a rain to
* Higher elevations under most threat for significant snow.
* Central ridge-valley areas not out of the woods.
* ECMWF/GFS develop steep mid level lapse rates...thunder snow?
Monday will be the most complicated and active day of the
forecast period. In a normal winter with normal cold air in
place, the expected track of a deep low up along or just off the
coast would be cause for joy among snow crows. But we are
abnormally mild ahead of this storm and that complicates the
During the day the models agree in intensifying the easterly
low level jet, as strong as 75 kt in some of the guidance.
SREF/GEFS show this to exceed 6 STD DEV in the anomaly plots.
Not a surprise with such an intense jet, ensembles also show a
high likelihood of more than an inch of QPF over much of
southern and central PA during the day Monday.
The complicating factor will be the amount of dynamic cooling
that is forecast to occur at the height of the storm as strong
warm advection and frontogenetic forcing support a period
intense upward vertical motion Monday morning into the
Initially we will see rain in all locations, but by mid morning
the higher elevations could mix with or change to wet snow that
will continue into the afternoon. Forecast soundings suggest
the snow could actually become more than just a higher
elevation threat by mid afternoon with thermal profiles even as
far east as AOO/UNV cooling sufficiently for all snow. If the
next run of models continues this idea of explosive dynamic
cooling as precip increases under the intense forcing, I would
anticipate some sort of headline to become necessary. The threat
is for several inches of heavy wet snow, especially favoring
the higher elevations from the Laurels northward, but possibly
even eastward into the central ridge-valley region of the CWA.
Another concern is the potential for flooding. Target area for
the heaviest rain is across the south central part of the state,
where orographic forcing at nose of powerful easterly low level
jet will play a role. Mean QPF from both SREF and GEFS max out
around 1.5 inches in this region, while FFG/FFH is around 2
inches/6hr. Have to stay alert for locally higher amounts such
as hinted at by the higher resolution NAM. Right now it looks
like a relatively fast moving event so will mention the
possibility of minor flooding in the HWO for this area late
It`s all going to make for a busy day for sure.
.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
The storm will reach our latitude between about 6-12Z Tuesday,
an old rule of thumb that dictated when the steady precip tends
to taper off. Upper ridging will quickly build into the region
later Tuesday into early Wednesday, bringing a short period of
fair and mild wx.
A pattern shift is advertised for the second half of the week
as low pressure takes up residence over eastern Canada, and
despite a tenacious ridge over the northern Caribbean and
Bahamas, models carve out a long wave trough over the eastern US
with a return to seasonable cold by the end of the week into
The ridge in the west and trough in the east is also usually a
good one for winter storminess, but the deterministic ECMWF and
GFS don`t show much more than a series of clipper type systems
that promise an extended period of clouds and scattered mainly
mountain snow showers that should continue through next weekend
into the week after.
.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --12Z TAFS sent.
Made some more adjustments to the package.
Earlier discussion below.
Made some moderate changes to 09Z TAFS, some of which will
carry into the 12Z TAF package. There was a small window
on Saturday where we had some improvement. Starting to see more
of a window today, as the system just east and south of our
area moves off the coast this morning.
Main problem will be late today into early Tuesday. Very deep
upper level low will result in a deep low forming well inland
across the southeast states today. This system will track
northward. At the current time, the low is fcst to move
just far enough away from our area, to edge down the chance
for strong storms, strong winds, and widespread heavy rain
late today into early Tue. However, still expect some gusty
winds and some heavy rain, especially across the southeast
later Monday into early Tuesday morning.
Mon...Rain/low CIGs likely.
Tue...AM rain/snow and low CIGs possible.
Wed...Reduced CIGs/showers possible NW.
Thu...MVFR/IFR in rain/snow showers mainly west.
-- End Changed Discussion --
Dense Fog Advisory until 10 AM EST this morning for PAZ005-006-
NEAR TERM...La Corte
SHORT TERM...La Corte
LONG TERM...La Corte