Area Forecast Discussion
Issued by NWS State College, PA-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 050252
Area Forecast Discussion
National Weather Service State College PA
952 PM EST Sun Dec 4 2016
High pressure will slide quickly off to the east of the region
this afternoon and evening. A weak frontal boundary but rather
potent upper air disturbance will pass through tonight. Another
storm system will affect the area during mid-week.
.NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
-- Changed Discussion --As precip overspreads the region, skin temperatures over the
Laurels are marginally cold enough to support some pockets of
freezing rain. Have decided to put an advisory for Somerset
country to cover the light icing event.
Latest Ensembles and deterministic models have been quite
consistent with the onset timing (and type) of precip that will
advance quickly NE later this evening within an area of robust
warm air advection aloft (and along/ahead of a potent mid/upper
level vort max).
The first few hours of the precip will be snow in most areas
(with perhaps some sleet/rain mixed in across the south where the
wet bulb 0C level will be AOA 1500 ft AGL). A longer period of
snow will occur across the central and northern counties of the
state...leading to a light accum of a coating to 2 inches.
There will be enough precip falling through the initially deep
layer of dry air and decent wet-bulbing via the 20-something
dewpoint air to make a light coating of snow/sleet across much of
Low temps will be mainly around 30 across the north where the
cold air is deep enough to support mainly snow...while readings in
the low/mid 30s are expected across the central and srn valleys
Will maintain a general 1-2" in the north and an inch or less in
the central and a little less still in the south. The precip could
turn to rain at the very end, but will likely just fizzle into
some patchy drizzle. This, too, could spell trouble if it lingers
into rush hour Monday morning and if temps can stay below
-- End Changed Discussion --
.SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/...
The fast zonal flow aloft takes the best forcing for precip off
to the east of the area early Monday. Will linger some sct
-SHSN or --RA at best in the east and along the west/high
elevations through about 15z Monday, but dry elsewhere.
Low clouds and the patchy, very light precip early will break for
some afternoon sunshine as a bubble (1020mb) of sfc high pressure
slides quickly east from the Ohio Valley.
High temps Monday afternoon will vary from about 40 across the
higher terrain of the north and west to near 50F in the SE.
.LONG TERM /MONDAY NIGHT THROUGH SUNDAY/...
Several successive systems will be moving through the region this
upcoming week. This will allow for a more tumultuous weather
pattern. The first will have a former cutoff low from old Mexico
as it`s forcing mechanism. The low will cross the border early
Monday and open up as it slides NE into the OH valley Mon night
and overhead on Tuesday. A broad but weak low will form over the
lower MS valley and perhaps do a split with one spot of lower
pressure going up the OH river and another one more to the south
which would eventually move over the DelMarVa peninsula.
The 850 MB temperatures show warm air advection aloft. The big
forecast question is the timing of frozen precipitation Monday
night through Tuesday. The current models have a weak upper level
trough that should only provide weak forcing. Without a very solid
low moving to our south, there still remains some question whether
all the precip will remain frozen. Similarly, without a distinct
low going to the west of us, there is a question that the warm air
advection will push over the entire area and turning things to
all rain. Have transition periods of change precipitation from
09Z Tuesday to 18Z Wednesday. The main area of mixed precipitation
remains over the central mountains. The southeast should have a
period of mixed precipitation before switching to rain. The NE
third of the area may stay cold enough to allow for an inch or so
of snow. There is a chance for freezing rain, though the precip
will be falling during the day, and temps should rise above
freezing after the precip begins but probably before noon passes.
Even the northern mountains should get into the mid to upper 30s.
The end of the week system brings another chance for
precipitation. This system is out ahead of a deep upper level low
moving through the Upper Great Lakes. There is some model
disparity on the timing however have increased POPS into Friday
night as the precip looks like a good bet around the Thu/fri
period and all solutions eventually bring this trough through. So
predictability is increasing, but timing issues remain. Best bet
for precip at this point is mainly rain over the SE as decent push
of warm air lifts ahead of the system, with a rain/snow mix then a
switch to snow as 850 mb temps are trending from -8 to -12 C.
Behind the trough, looks like a chilly weekend in store with a
potential sharp drop off in temps.
.AVIATION /03Z MONDAY THROUGH FRIDAY/...
Brief period of VFR conditions across all of Central Pennsylvania
at 00z, but will be short lived as snow/rain system rapidly
approaching from the west.
Snow moves into northern mountains and higher elevations
tonight, where a period of IFR conditions are expected. Rain and
snow for central airfields, while a mainly rain event in the
System exits early and quickly on Monday from west to east.
Lingering lower stratus expected in the mountains of the west and
north, but elsewhere expect conditions to improve to VFR by
Mon afternoon/evening...No sig wx expected.
Tue...Mixed precip/low CIGs possible, especially late.
Wed...Lingering low CIGs possible.
Thu...Mixed precipitation event - low CIGs possible.
Fri...Blustery and much colder with NW mtn and Laurel Highland
restrictions in SHSN and areas of enhanced Lake Effect Snow.
-- Changed Discussion --Winter Weather Advisory until 4 AM EST Monday for PAZ033.
-- End Changed Discussion --
NEAR TERM...La Corte