Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1036 am EST Monday Nov 24 2014
near-record warm temperatures are expected over much of the area
today...before cold air arrives tonight behind a departing low
pressure system. Another area of low pressure will move along the
middle Atlantic coast Wednesday into Thursday... bringing a chance of
significant snow to the eastern half of Pennsylvania. Another
shot of cold air will follow for next weekend.
Near term /through tonight/...
steady or slowly rising temperatures are the norm this morning as
warm front lifts towards the fingerlakes. Steadiest and heaviest
rainfall has long since tracked north and east of my area on the
nose of a 55-65kt 850 mb jet lifting into New York state. Lighter
showers still traversing the higher terrain of western PA as well
as the lower susq River Valley...but these will decrease later
this morning as the warm front continues to lift north upstate New York.
Short term concern is for strong gusty winds across the higher
elevs of the alleghenies later today. Strongly coupled southwest
winds should easily create in the upper 30kt range...likely
increasing to occasionally 40-43 kts in the late afternoon and night.
Wind Advisory remains in effect 17z-09z Tuesday for the northwest mountains
and Laurel Highlands.
Clearing and strong mixing will push afternoon temperatures to near-
record levels. The biggest temperature bust potential area /stay too
cool vs forecast/ will be the northeastern mountains cold front timed to
cross the region late this afternoon and evening...but cooling
will not be sharp as deep nearly parallel flow promotes only slow
southeast progression of Post frontal air mass. After a round of
evening showers...expect the remainder of tonight to be dry as
cold advection persists on west-southwest flow. Mins will not be very cold...
only ranging from around 30f north to the lower 40s southeast.
Short term /Tuesday/...
boundary layer flow will slowly back and weaken on Tuesday...while
a weak area of high pressure drifts into the Ohio Valley and into
the western PA Tuesday night. Tuesday will be the calm before the
storm as all eyes shift southward for the evolution of what could
be the first widespread significant snowfall across much of the
eastern half of central PA Wednesday.
Cold air will continue to filter in aloft...and highs Tuesday will
be some 20 degrees cooler than the near record readings of Monday
Long term /Tuesday night through Sunday/...
potential for sig winter impacts from low pressure moving up the
East Coast on Wednesday/Wednesday night. Will continue to inject
interpretation of the latest model guidance with each 3-hourly
update to guide decision support leading up to the prime travel
period for the Thanksgiving Holiday.
Highly amplified and active upper air pattern will bring a period
of active weather through the coming week. The 500mb configuration
will feature anomalous ridging along the West Coast and in the
western Atlantic with a full-latitude persistent trough ebbing
and flowing over the central and eastern U.S.
After the exit of Monday/S low pressure area...colder temperatures
return on brisk west/SW flow for Tuesday dropping highs some 20-25f from
previous days readings. We/ll also see the return of light snow
showers in the western higher terrain.
Then focus will turn to a wave currently dropping southeast from British
Columbia and Washington state...which will spawn an area of low
pressure over the southeast US Tuesday night...that will likely move
north northeastward just off the East Coast Wednesday into
12z/18z operational and gefs runs along with the 21z sref are
becoming fairly well clustered with respect to the location of the
near...to sub-1000 mb surface low early Wednesday evening /near...and up to
about 200 nm east of Delaware-Maryland-Virginia peninsula/.
There is still much uncertainty at this 60-72 hour timeframe
before the event...with respect to the exact track of the surface low
and associated snow/rain amounts.
Cold air will be in place Wednesday morning as a /weak/ high pressure
ridge retreats to the north ahead of the approaching low.
Northerly flow over central PA not particularly strong in any
model...but a shortwave looks poised to slide in from the Great
Lakes on Wednesday to add some synoptic lift to a rapidly deepening and
fast moving surface low.
The 12z European model (ecmwf) and it's ensemble are very similar hugging the surface
low along the shoreline...while US/Canadian models and their
ensembles are further east by 100-200 nm. Experience shows that
the lack of a significant blocking high to our north or
northeast...favors a more western track /similar to the ec and its
ensemble/. Should the westward trend continue even further with an
earlier injection of northern stream energy into the southern stream
system...it/S conceivable that our far southeast zones /near klns and
kmdt/ could even see a mix with sleet and rain for a period that
would hold down accumulations.
Precipitation may start off early Wednesday as a mix of rain and snow in the
southeast...but cooling temperatures aloft should convert all precipitation over to
snow by midday. As is a general rule with these types of events...
there will likely be a sharp drop off in accumulations on the northwest
edge of the heavier snows. Biggest potential impacts in our County Warning Area
will be the central mountains and susq valley...where potential for a
several hour period of heavy accumulating snow will exist. But
again...small changes in the ultimate track could lead to
modifications of snowfall forecasts. The take away...though the
details remain uncertain...there will be sig impacts to travel
along the U.S. East Coast on one of the busiest days of the year
/Wed/. Plan accordingly.
Colder air remains in place late in the week as scattered snow showers
return to the western higher terrain. Temperatures look to gradually
modify late weekend heading into next week...with no big storm
systems expected after Thanksgiving.
Aviation /16z Monday through Friday/...
deep system lifting NE. Winds still from the southeast to S...thus
low level wind shear for a few more hours. VAD winds at 3000 feet about 30
to 40 knots.
Strongest wind fields lift NE this after.
15z taf package sent.
Earlier discussion below.
The upper level trough has moved northward with regional radar at
11z shows most of the precipitation has all but ended. Ceilings and
visibilities continue to improve...with MVFR conditions at most taf
sites...with jst and aoo have VFR due to strong southwesterly
flow. Conditions will continue to improve quickly...with VFR ceilings
and visibilities expected by 15z at the latest. A warm front will lift
northof the region and the VFR conds will continue through the
day. A cold front will make its way through the region tonight.
This will allow the winds to shift to a more westerly
direction...and another round of low level wind shear will be possible this
evening...mainly across the central mountains. A cold front moving
from the west late this afternoon into the evening hours will be
accompanied by rain showers across the West Mountains...possibly producing a
brief visibility reduction at kbfd or kjst.
Tuesday...no sig weather expected.
Wednesday...snow/low visibilities poss eastern PA.
Thursday...-shsn/reduced visibilities poss northwest mountains
Friday...no sig weather expected.
Wind Advisory until 4 am EST Tuesday for paz004>006-010-011-