Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
1249 am EST Tuesday Dec 1 2015
an upper low over the plains states will slide across the Great
Lakes through midweek. A period of rain will result tonight into
Wednesday...when a cold front will push through ending the rain
but bringing some snow showers to the northwest mountains
Wednesday night. Temperatures will be at or slightly above
seasonal normals all week long...but moderate slightly for the
Near term /until 6 am this morning/...
Freezing Rain Advisory allowed to expire for the southern
alleghenies...as penndot reported Road only isolated higher
elevation overpasses hovering near or slightly above freezing.
Expect boundary layer to warm sufficiently to preclude additional
Upslope flow and increasing southerly 850mb winds transporting
moisture northward...with patchy light rain and drizzle persisting
throughout central and southern portions of central PA this
evening. Activity continues to drift northward late this evening and
will overspread much of the central and eastern portions of the
northern tier by midnight. Best chances of measurable rain hold
off until the daylight hours Tuesday however. Expect steady or
slowly rising temperatures overnight...with mins having already occurred
or occurring late this evening for most...and ranging from the
middle to upper 30s across all but the higher elevs (mainly 1700 feet
and above) which will hover near 32f for a few more hours this
Short term /6 am this morning through 6 PM Wednesday/...
a very strong upper low closed up over the High Plains will bring
a plume of moisture up from the southwest as a more-constant rain
spreads over the region from the SW.
Rain is expected to be off and on Tuesday into Wednesday. The upper low
deepens as it moves into the upper Great Lakes. The moisture plume
is not all that deep/impressive...with precipitable waters only around an inch.
While that is above normal...it is not all that unusual. The
cold/occluded front arrives on Wednesday morning. Some spread in
the timing of the front is still seen. European model (ecmwf) is slower with the
frontal passage. It develops a weak low along the front over the
Gulf Coast states and brings it up the eastern side of the
Appalachians on Wednesday. Quantitative precipitation forecast values look to range from 0.50
inches over the northwest to 1.00-1.50 over the southeast.
Highs in the 40s on Tuesday will be about normal in the southeast but
10f above normal in the northwest. A very mild night for Dec 02 in store
as lows remain in the upper 30s and 40s.
Long term /Wednesday night through Monday/...
low pressure wave developing along cold front pushing east of the
Appalachians Wednesday will be the focus for enhanced precipitation...as it
tracks over eastern PA and intensifies a bit into southern New
England. Model data suggests some locally heavy rain is possible
along the low track...but organized short-duration flooding is not
expected at this time given dry antecedent conditions.
Upper low with steadily falling heights will cross the area
Wednesday night into Thursday. Increasing northwest flow on the backside
of the departing low will direct colder air over the Great Lakes
and produce lake enhanced snow showers focused over the northwest
alleghenies on Thursday. Used wpc winter precipitation guidance for snow
totals which indicate a fairly high confidence for at least minor
accumulations especially in the favored snowbelt in Warren/McKean
counties along and to the north of Route 6.
High pressure will dominate the weather pattern and provide fair and
tranquil conditions into early next week. After a seasonable "cool"
down to end the week...look for temperatures to climb back above
normal into next week.
Aviation /06z Tuesday through Saturday/...
looking at mainly IFR conditions into Wednesday morning.
Main adjustment to 06z tafs was to adjust for where current
and projected rainfall is...mainly eastern areas today.
For tonight...models show more in the way of widespread
rainfall as front moves in from the west.
Borderline for low level wind shear for western areas the next few hours...but
left it in the forecast...given it was in already.
Looks like all areas above freezing now.
Earlier discussion below.
A moist southeasterly flow has overspread the region this evening with
low clouds already established over the higher terrain of central
PA at 02z. MVFR ceilings still noted at the lower elevation airfields
from kipt south through kmdt/klns. However...there is a high
confidence in deteriorating conds there overnight...as rain
arrives and ceilings fall. By late tonight...expect widespread
IFR/LIFR ceilings across the entire region. Other area of concern will
be the possibility of marginal low level wind shear...as core of stronger winds
aloft lifts across the area overnight and early Tuesday. Based on
examination of latest model soundings...have included low level wind shear at
Little Prospect for any improvement on Tuesday...as moist southeasterly
flow continues to funnel moisture into the region. There remains
a high confidence in rain/widespread IFR ceilings through Tuesday.
Wednesday...rain/low ceilings likely.
Thursday...am shsn/visible reductions poss kbfd.
Fri-Sat...no sig weather expected.