Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
340 am EDT Sat Mar 15 2014
a weak cold front will pass through the state early this
morning...followed by a secondary cold front late today. An area
of low pressure will track south of PA Sunday night and Monday.
Another low pressure system will likely track west of Pennsylvania
in the middle of next week.
Near term /until 8 am this morning/...
regional radar showing a band of rain showers across the northwest mountains at 0530z
in associated with cold front. Still expect band of rain showers to dissipate as
they pass east of the Allegheny plateau...mainly the result of
downsloping westerly flow. Latest rap and nampara simulated
reflectivity support this idea...so will mention high probability of precipitation across
the West Mountains and just a chance of a -shra across the susq valley
during the pre-dawn hours.
An examination upstream observation and latest model soundings suggests any
changeover to -shsn over the northwest mountains will occur after the bulk of
precipitation has passed...so removed overnight snow accums entirely.
Temperatures on track to bottom out by dawn from around 32f across the northwest
mountains...to the l40s across the susq valley.
Short term /8 am this morning through 6 PM Sunday/...
secondary cold front trailing south-southwest from clipper over S Quebec will
push southeast across the County Warning Area late today...but with little in the way of
precipitation /except for a few snow showers across the northwest mtns/.
Sky cover during much of Saturday will range from partly to mostly
sunny in the southeast...to mostly cloudy in the kbfd vicinity.
West-northwest winds will gust to the middle-upper 20kt range during
the day Saturday...making it feel noticeably cooler than the
otherwise slightly above normal temperatures in the 30s northwest...to lower and
middle 50s in the susq valley.
Tricky temperature forecast for Saturday night as high pressure builds east
from the upper Great Lakes and much colder air filters south in to
the state. Main question will be just how much middle and high clouds
will spread east from the Ohio Valley along the axis of a
strengthening east/west jet core.
For now...will maintain the fairly large north-south temperature spread
from the lower teens across the north...to the upper 20s in the
Long term /Sunday night through Friday/...
surface anticyclone...with origins over the northwest territories...will dive
southeast across the Great Lakes late in the weekend...reinforcing the cold air
across central PA. Meanwhile...a southern stream shortwave and associated
surface low will be gathering Gulf of mex moisture over the lower MS
valley/Delta Region with a baroclinic zone setting up from Missouri to
Virginia. Models are coming into better agreement on southward surge of
Canadian air associated with surface high into the northeast states. Gefs
mean 925 temperatures of 1-2sd blw average support high temperatures Sunday of only
the m20s north mountains and perhaps around 40f in southern valleys.
Upper level troughing remains a fixture across southeast Canada and
much of the eastern Continental U.S....which should support near to below normal
temperatures in central PA through most of the period.
There are two systems to focus on for this cycle.
1) surface wave or waves migrating northeastward from Gulf Coast states across
the southeast and off the Outer Banks of NC Mon-Tue.
2) plains surface low and trailing cold front moving east/NE through the Great
Lakes and applchns Wed-Thu.
The key feature of interest /system #1/ remains the main forecast
challenge in the medium range. Have increased probability of precipitation across
the region Sun night-Monday based on blend of 00z guidance...all
of which now track surface low close enough to bring snow to at least
southern PA. A poor-mans ensemble of the operational
models/ensemble/HPC guidance...suggest a moderate snowfall is
possible across the southern part of the state sun nite-Monday.
Concerning system #2...it looks as though a surface ridge should
separate the departing system #1 and surface low lifting northeastward from the
plains into the Great Lakes. There is a large spread in the timing
of this system...with the GFS/gefs trending slower into midweek.
Confidence is low with this system...and stayed close to guidance
for days 6-8.
Aviation /08z Saturday through Wednesday/...
a weak cold front passing through the state early this morning
will produce a 2-3 hour period of rain in western/central
portions of County Warning Area before precipitation weakens as it progresses
eastward. The front will bring temporary reductions and very gusty
SW winds /and llws/. Winds may diminish a bit immediately behind
the front...but will pick up again after sunrise.
Scattered light snow showers will develop by middle morning over northwest mountains as
colder air begins to filter in. This will be accompanied by ceiling
and occasional visibility reductions. Ceiling restrictions will also be poss
through about 15z across Laurel Highlands including kjst.
Elsewhere conditions should remain VFR as stiff winds shift more
westerly...increasing downslope component. Gusts during the day
will increase to 30-40mph as a secondary cold front pushes
through. Low level wind shear will decrease as core of jet shifts to our NE.
MVFR ceilings may linger into Sat night at kbfd...but otherwise VFR
should be the rule. Breezy west-northwest winds will persist
however. An area of low pressure will track south of PA Sunday
night and Monday.
sun...no sig weather expected.
Sun night-Mon...snow with restrictions possible southern PA.
Tuesday night-Wed...periods of MVFR to IFR along with scattered rain/snow
showers possible as a warm front lifts northward across the region.