Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
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FXUS61 KCTP 231020
Area Forecast Discussion
National Weather Service State College PA
520 AM EST Mon Jan 23 2017
A storm will move through the Carolinas early today before
redeveloping along the coast and moving up just east of NJ
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.
.NEAR TERM /THROUGH TONIGHT/...
* Major cyclone to affect the region today and tonight
* Elevation dependent snow storm likely
* Heavy wet snow not out of the question even into central
* Strong easterly LLJ 50-65kt/5-7 sigma
* High probability of at least 1" QPF over much of central PA
* Explosive dynamic cooling leads to steep mid level lapse
The deep storm that has been responsible for several rounds of
severe storms and deadly tornadoes over Dixie, will move east
and redevelop in the vicinity of the Delmarva coast, before
swinging up along or just off the NJ coast.
The wind has picked up a bit tonight allowing the very low
visibilities to mix out somewhat as spotty light rain and
drizzle have few NW over the area.
The HRRR shows the rain continuing to fill in as it moves NW
into central PA this morning. Then things get complicated and
interesting. As strong vertical motion forces rapid dynamic
cooling aloft, precipitation type issues will arise quickly by
late morning and this afternoon. We start off so anomalously
warm it`s hard to believe a significant snow storm is possible
but it looks very likely for at least my northern higher
elevation counties. The deterministic ECMWF shows several
inches of snow even down into the Laurel Highlands. The EC
ensemble is even more generous with its depiction of 6+ inches,
though it is notoriously generous with the snow its algorithm
produces. Right now I show a rain to rain or snow scenario for
central areas where the higher elevations seem most at risk for
accumulating snow, but even down in the valleys, if we see heavy
enough precip rates we could share in the snow-joy.
A tightening pressure gradient between low pressure in the
Carolinas and high pressure in eastern Quebec will produce
strong/gusty east winds this morning into the afternoon, the
best threat area being our SERN zones. We tend to have a hard
time mixing the best winds down under what is essentially a cool
air damming set up, but with 50-65 kts aloft, strong gusts
cannot be ruled out.
It`s a very complicated situation and will likely lead to many
near term tweaks as things play out today.
I generally used the ECMWF to show the steadiest/heaviest snow
lasting into tonight over about the NERN 1/3 - 1/2 of my
forecast area as the upper low swings offshore and we see the
deformation zone gradually rotate through. Meso-scale banding
under this feature could cause locally higher amounts than the
general 6-10 inches I have in the forecast at this time.
The snow should begin to taper off to scattered snow showers
.SHORT TERM /TUESDAY/...
As the storm system pulls away toward the coastal waters south
of New England tomorrow, rain or snow showers will tend to be
most frequent in the morning and become more scattered in the
Highs in the mid 30s to mid 40s will still be several degrees
warmer than normal.
.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
After a brief break and mild conditions for mid week, 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 next weekend.
It points to a prolonged period of cloudy breezy and colder
weather with mainly mountains snow showers that will
occasionally bleed down into central areas.
.AVIATION /10Z MONDAY THROUGH FRIDAY/...
-- Changed Discussion --09Z TAFS sent.
Cooling tops over WV now, in the area that is fcst to have
a cold pocket at 850 mb form.
The second part of the puzzle is if the area of precipitation
will fill in. At the current time, several bands of rain well
to the south of our area.
Thus for the next few hours, the main issue is gusty winds.
Later on, expect the area of rain to fill in. Then at least
sites like BFD and JST are likely to see some heavy wet snow
this aft into tonight.
Other problems will be LLWS, given that strong winds have
formed since midnight.
Some chance of thunder, given strong upper level support.
Tue...Widespread sub-VFR with some improvement by aftn. Rain/snow
ending in the morning. Gusty winds from NNW decreasing late.
Wed...Low cigs/rain possible western 1/2. Breezy late.
Thu-Fri...MVFR/IFR in rain/snow showers west. MVFR to VFR east.
-- End Changed Discussion --
Winter Weather Advisory from 4 PM this afternoon to 7 AM EST
Tuesday for PAZ005-010>012-017-018.
Winter Storm Warning from 1 PM this afternoon to 10 AM EST
Tuesday for PAZ006-037-041-042.
Wind Advisory until 4 PM EST this afternoon for PAZ057-059-
NEAR TERM...La Corte
SHORT TERM...La Corte
LONG TERM...La Corte