Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
425 PM EST Tuesday Nov 25 2014
high pressure will recede to the northeast tonight. A storm
system beginning to form off the Georgia/South Carolina coast
will move up along or just off the eastern Seaboard on
Wednesday...bringing the potential for significant snow mainly to
southern and eastern PA. Another shot of colder air will follow
for the end of the week...before temperatures warm up a bit over
the weekend and early next week.
Near term /until 6 am Wednesday morning/...
high clouds thinning out this afternoon above weak ridge of high
pressure while stratocu persist over northwest mountains back toward the
colder air over the Great Lakes. Overall not a bad day for late
November in central PA as temperatures peaked several degrees above
normal /though notably cooler than Mon/...with a breezy west/SW wind.
Winds will decrease quickly heading into this evening as pressure
gradient continues to weaken. Limited clouds early will allow
temperatures to slip into the 20s before leveling out overnight.
Over past 24h...model guidance has come into good agreement on
evolution of developing low pressure area being born along the
Georgia/SC coast in response to a potent shortwave approaching from the
Mississippi Valley. The GFS/gefs has trended westward while the
ec looked to take just a slight lean eastward...with the result
now being a good consensus on likely surface low track. The
system aloft takes on a negative tilt as it moves up the eastern
Seaboard...with the surface low made to track along then just
offshore of the East Coast Wednesday.
For the overnight...precipitation overspreading the southern tier
counties quickly after 08z...with quantitative precipitation forecast approaching a tenth of an
inch by 12z. Temperatures aloft and on the surface suggest that precipitation
starting over southern /especially southeast/ areas late tonight will
likely be at least a mix of rain and snow with light snow on the
northern edge. Simply...precipitation will move into southern half of County Warning Area
before sunrise and will be light...but quickly intensify during
the morning rush hour across the south.
Short term /6 am Wednesday morning through Wednesday night/...
winter storm warnings/advisories now in effect.
A low pressure system develops and intensifies as it tracks from
the Carolina coast at 12z Wednesday to off the New Jersey coast by 00z Thursday...
bringing biggest impacts to central PA during the day Wednesday.
Confidence is growing in the storm track with GFS coming in line
with the European model (ecmwf) closer to the coast...which will push the quantitative precipitation forecast
shield a bit further west. Precipitation will be ongoing in the south by
sunrise...and spreading quickly into the central and northeast by
middle morning. Any rain will quickly change to snow in the southeast as
column cools. Period of heaviest intensity precipitation will be Wednesday
morning through middle afternoon...where snow rates could be 1-2
inches per hour in the warning area. Latest westward graphics continue
to show a swath of 6-8 snows over the southeastern 1/3 or so of my forecast
area. Confidence for sig snows up into central/northwest PA not as high
given the lack of a sig easterly low level wind anomaly in the
ensembles...and a shortwave sliding in from the west which may
sharpen gradient of snow. But for a couple inches of snow and
impacts on the busiest travel day of the year we strung an
advisory over the northern edge of the warning area.
Snow should taper off quickly by late Wednesday after/Wednesday evening as storm
quickly moves into New England. Flow transitions back to a northwest fetch
across the lakes...with light scattered snow showers poss by Thursday morning
in the upslope of the western higher terrain.
Long term /Thursday through Tuesday/...
upper troffing over the eastern third of the country at the start
of the long term period is forecast to flatten out into an
extensive west to east zonal flow pattern covering much of North
America. Heights over the northeastern U.S. Are then forecast to
rise from late in the weekend Onward as the caboose in the current shortwave
train exits the East Coast on Friday and energy approaching the
Pacific coast closes off and builds heights over the western and
A shot of cold air will move into the region for Thursday and
Friday behind the aforementioned caboose shortwave. This wave may
also support an area of precipitation moving west to east across the state
Thanksgiving day. Additionally...this push of energy/cold air
should generate the usual Post frontal lake and orographically
enhanced snow showers in the wake of the departing storm system
with western and northern areas seeing the best chance of
scattered light snows...while the rest of the region sees little
or no snow shower activity at all.
A broad west-southwest flow aloft associated with the rising heights will
make this cold shot temporary with warmer air beginning to make a
return by Saturday. Highs will return to near or even a tick above
normal by the weekend before cooler air approaches again for early
A frontal system in advance of the warm air will move across the
state on Sunday...bringing the best chance of precipitation during the
Aviation /21z Tuesday through Sunday/...
a few lower clouds over the northwest and far west...but most areas
just some hi and middle clouds. Breezy across much of the area.
Anyway...looking at mainly VFR conditions through this evening.
A low pressure system forming on a stalled front will lift
NE on Wednesday. Snow will move in shortly before sunrise on Wednesday across
the south. Conditions will quickly go downhill. Snow could start
as rain across the southeast...before temperatures cool down. LIFR to IFR
conditions will be across much of the area on Wednesday.
Improving conditions for Wednesday night into Thanksgiving...as the
storm moves away. Not seeing much cold air or wind behind
Rapid warm up for the weekend into early next week...should
limit lower clouds. Next cold front could stall across or just
to the north of the area by late Sunday.
Thursday...am fog poss south. Evening -shsn/reduced visibilities poss West Mountains
Fri-Sat...no sig weather expected.
Sun...mainly VFR...perhaps a shower along stalled front.
Winter Storm Warning from 3 am Wednesday to 4 am EST Thursday
Winter Weather Advisory from 3 am Wednesday to 4 am EST
Thursday for paz012-017-018-037-041.
Winter Storm Warning from 3 am Wednesday to midnight EST
Wednesday night for paz024>028-033>036-056>059-063>066.
long term...la corte/gartner