Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
520 am EDT Monday Mar 17 2014
an area of low pressure will track well to the south of Pennsylvania
early today. A ridge of high pressure will build across the
region later today and Tuesday. Another low pressure system will
likely track west of Pennsylvania by midweek.
Near term /until 6 PM this evening/...
a loop of satellite-derived precipitable waters shows a broad plume of Gulf of mex
moisture streaming into the middle Atlantic region in advance of
approaching positively-tilted trough. Snow is falling south of the
Turnpike where this moisture is overrunning shallow Arctic air
mass. Upstream radar imagery and latest near term model data suggest
the steadiest snow will come to an end by around 12z...as upper level
shortwave passes east of the region. However...easterly wind
anomalies will remain focused along the S tier counties through
early afternoon...likely supporting a bit of lingering light snow despite
waning lg scale forcing.
No change to snow accums...with an expected 1-3 inches south of
the Turnpike...with a bit more over Somerset Colorado due to upslope
enhancement. Very dry air across the northern half of the state
should preclude snow from making it further north than an Altoona
to Harrisburg line.
Any lingering light snow/flurries should end by early afternoon across
the S tier...as surface low passes off the East Coast and lg scale
subsidence overspreads the area. Back edge of the cirrus shield is
already working into the northwest mountains at 09z and expect clearing to
work into the central and northern counties by late am. Across
the south...lingering moisture trapped beneath subsidence inversion is
likely to result in lingering clouds between 1-3km based on model
High pressure and associated cold air mass parked north of Lake Ontario will
result in another very chilly day for middle March. Sunshine should
push readings into the middle 30s across the central valleys.
Elsewhere...readings will struggle to reach freezing...even across
the south where clouds are likely to persist.
Short term /6 PM this evening through 6 PM Tuesday/...
surface high will ridge southward across the region tonight...resulting
in a fair/cold night. Persistent southeasterly low level flow into the
Appalachians will likely result in lingering low clouds across the
Laurel Highlands/SC mountains can/T completely rule out a touch of
fzdz along the ridgetops of Somerset/Bedford Colorado overnight...but
surface-850mb layer doesn/T appear quite moist enough to support it.
Strengthening March sun angle should help to mix out any low
clouds across the SC mountains on Tuesday. However...central PA will
remain under the influence of high pressure over new eng...circulating
cold southward along the east side of the Appalachians. Gefs mean
925 temperatures support maximum temperatures no better than the l40s over most of
region...some 5-10f degree below normal.
Long term /Tuesday night through Sunday/...
moistening southeasterly flow across southern PA could potentially yield a
bit of freezing drizzle or drizzle across the central mountains early
Wednesday. Focus will then shift toward surface low tracking west of PA...which
will bring a good chance of rain showers along trailing cold front late in
the day and Wednesday evening.
Fairly little spread among medium range guidance through the end of the
forecast cycle...leading to relatively high confidence into the
weekend. All guidance indicates the next sig weather feature to affect
the area will be a clipper working along the north tier Continental U.S. Late in
the week. Associated surface low is prognosticated by bulk of model data to track
through or just north of PA on Saturday. Thus have increased probability of precipitation in
the Friday night/Sat time period. Current guidance suggests some
mixed precipitation is poss across northern PA...with rain most likely in
Latest gefs and ec ensemble data indicate a surge of very chilly
air will follow the clipper for late in the weekend. Ens mean 800 mb
temperatures of -14c on Sunday indicate sub-freezing highs are possible
across the north mountains
Aviation /09z Monday through Friday/...
comms issues continue at kbfd...and Don/T expect it to be fully
back online until the daytime hours on Monday. Until then...will
not be issuing unscheduled amendment.
An area of low pressure located well to our south will continue to
move east through Monday. The northern edge of its snow shield
will brush far southern Pennsylvania overnight...bringing light
snow and associated visibility/ceiling reductions to kjst-kaoo through
12z...and likely impacting kmdt-klns starting around 07-08z /as
low levels starting out quite dry with NE winds feeding drier air
into those areas/. MVFR conditions will be the rule in these
areas...with occasional IFR visibility poss. VFR conditions will persist
High pressure will build southeast across the region Monday and
Tuesday....with primarily VFR conditions...though MVFR ceilings may
remain stubborn around kjst. Another low pressure system will
likely track NE into the Great Lakes region by midweek...with
restrictions again becoming likely Tuesday night into Wednesday.
Monday...MVFR early south. Otherwise VFR.
Tuesday...mainly VFR. Ceiling restrictions poss in Laurel Highlands.
Tuesday night-Wed...periods of MVFR to IFR along with scattered rain/snow
showers as a frontal system moves through the region.
Thursday...MVFR possible in the mountains. VFR over central and eastern
Friday...VFR most of the day...few showers possible late Friday.
Winter Weather Advisory until 11 am EDT this morning for