Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
700 PM EST Friday Dec 19 2014
high pressure centered over the western Great Lakes will slide
east across Pennsylvania this weekend...bringing dry weather with
lighter wind. A deep upper trough and associated surface low will lift
northeast through the Great Lakes during the middle of next week
likely bringing US rain and wind for Christmas evening...then blustery
and colder conditions for Christmas day with scattered snow
Near term /until 7 am Saturday morning/...
7 PM update...
big breaks in clouds locally. Nearly flow is shoving the clouds down
into the Poconos and trying to get them into leb/lanc cos. At this
point...will continue to count on the downslope to keep it from
going totally overcast...but some increase in clouds over the next few
hours in the southeast is probably a good call. Otherwise...the subsidence
in between the northestern and southeastern parts of the state may continue to
open up bigger breaks. Will have to tweak northwestern min temperatures as they
are extremely close to going mins at this time. Elsewhere...dewpoints and
only slow decrease in covg look like the mins are okay for now.
stubborn...albeit shallow strato cumulus cloud deck trapped below a
moderately strong subsidence inversion /based at around 2-3kft
above ground level/ will persist across much of northern and western Pennsylvania
late today into Saturday...while partial clearing occurs across
the lower susq valley and surrounding areas.
Temperatures will remain steady through late this afternoon under the
10-15 knots nwrly flow. Readings will vary from the middle to upper 20s
across the northern and western mountains...to the lower 40s in
A weak surface ridge will move to near the Penn/Ohio border by 12z
Saturday...but the weak westerly isentropic lift along the 285k
Theta surface...and some shallow moisture being advected southward into the
northern mountains of Penn from Lake Ontario...will maintain mostly cloudy
to cloudy skies. Little more than a few flurries or spotty -fzdz
will fall from this thin cloud layer across the higher terrain of
The Laurels and in vicinity of kbfd.
After a partly cloudy late afternoon and evening in the southeast part of
the County Warning Area...a broken layer of strato cumulus is expected to drift southeast /or
form/ across the region overnight.
Due to the northwest-southeast gradient of decreasing clouds...low temperatures at
daybreak Sat will be in a rather tight range...from the upper
teens to lower 20s across the mountains...to the lower 20s in the
Short term /7 am Saturday morning through Saturday night/...
a ridge of high pressure...lighter wind...and associated drier air
mass will build east across the state Saturday...providing the
area with fair weather.
High res model data continues to paint a mostly cloudy picture for
much of the region Saturday into Saturday night...though periods
of sunshine are likely throughout the Central Ridge and valley
region...and Susquehanna River valley.
Warm air advection aloft in advance of shortwave lifting out of the miss valley
will likely spread some thin cirrus over the lower/thin strato cumulus
cloud deck present across the region Saturday. All 12z operational
model data continues to support a dry day with surface ridge and low
precipitable water airmass over the state. Maximum temperatures should be fairly close to
seasonal norms near 30 across the mountains...and middle to upper 30s in
Mostly cloudy skies with light wind Sat night will yield lows in
the lower 20s across the mountains...and generally the middle 20s
Long term /Sunday through Friday/...
high pressure will provide tranquil weather on Sunday...with partly to
mostly sunny skies and seasonable temperatures. After that...the weather
will become increasingly unsettled as next week progresses.
Clouds will increase Sunday night into Monday...as high pressure loses
its grip and a weak area of low pressure organizes over the southeastern United
States. Light precipitation will work northward into Pennsylvania late Monday
into Monday night and continue into Tuesday. Initially...conds will
be cold enough for the possibility of some wintry precipitation.
However...warmer air will make its way northward later Monday night into
Tuesday and gradually change any lingering precipitation over to plain rain.
A more significant storm system will get organized over the
Mississippi Valley Tuesday night before pushing northward into the Great
Lakes on Wednesday. This system will draw even milder air northward into the
region...and provide a rainy and breezy Christmas evening day.
As this system drifts northward into southern Canada...colder air will wrap
into the region on blustery west winds. A changeover from rain to
snow showers from west to east across PA is possible late Wednesday/Wednesday
night. Scattered snow showers will continue into Thursday across mainly
northern and western PA.
The chillier airmass looks like it will be short-lived...with
operational models and the gefs showing 850hpa temperatures already
beginning to rise next Friday.
Aviation /00z Saturday through Wednesday/...
low level nwrly flow and orographic forcing of a shallow moist layer
will continue to produce plenty of clouds across the northwest 1/2 to
2/3rds of the state with mainly MVFR broken-overcast ceilings through
tonight. Kjst and kbfd may teeter on the upper end of IFR for a
few hours later tonight /after 06z/. In contrast...the southeast Penn
airfields such as kmdt...kthv and klns will see mainly VFR...with
sky conditions varying sct-bkn030-040.
Northwest winds of 10-15 kts with higher gusts will decrease to 8
kts or less later tonight and Saturday.
High pressure builds east across Penn Saturday...with broken-overcast ceilings
varying between MVFR over the higher terrain of the north and
west...to scattered-broken VFR in the valleys.
Sun...no sig weather expected.
Monday...low ceilings with light rain/snow possible. Becoming breezy.
Tuesday...low ceilings with rain likely. Breezy.
Wednesday...mild with periods of rain of varying intensity...leading to
MVFR to IFR. Also...windy with low level wind shear.