Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
415 PM EST Thursday Dec 18 2014
northwest winds will keep flurries and scattered light snow
showers over the north and west into Friday morning. High
pressure will slide down from the upper Great Lakes and provide a
generally fair period for most of the weekend. An unsettled pattern
will set up in the first part of the new week. A weak low pressure
area could bring light rain or snow to the area on Monday. Then a
significant area of low pressure is expected to develop over the
Midwest and upper Great Lakes. This will likely produce rain for
the state on Wednesday...followed by strong west winds and
scattered mountain snow showers for Christmas day.
Near term /until 6 am Friday morning/...
seasonably cold northwest flow across the eastern lakes will
remain in place through Friday with the typical downwind stratus
across most of central PA. Cyclonic flow aloft on the backside of
Newfoundland Upper Cutoff/Rex blocking pattern will keep weak or
nearly neutral cold advection over the region. A southern stream
wave streaking eastward from the Tennessee River valley Thursday afternoon
will produce areas of very light snow across the Laurel Highlands
into the south central mountains this evening with little if any
accumulation expected. West facing slopes of the west central
mountains and Laurel Highlands may see a localized coating to an
inch or two of snow as the upper and boundary layer flow align
for a period late tonight into Friday morning.
Otherwise expect widespread stratus to persist across most of
central PA. The southeast will likely see some dissipation by
Friday morning. Surface high centered over the northern Great
Lakes and eastern Quebec will keep north/northwest boundary layer
flow going through Friday morning...translating to surface winds in the 7
to 11 miles per hour range.
Short term /6 am Friday morning through 6 PM Friday/...
upper forcing slides east of the region early Friday morning...
with expansive surface high pressure building over the area in the
afternoon. Thus...the amount/coverage of the snow showers and
flurries should diminish completely on Friday. Mins will stay a
little milder than climatology with clouds around. Maxes on Friday very
similar to today...with 30s for the mountains and near 40 in the
low lands with the help of some downslope warming.
Long term /Friday night through Wednesday/...
high pressure will shift slowly eastward from the Great Lakes
into northern New England by 12z Monday. Residual low level
moisture along with northern stream shortwave energy attempting to
undercut an upper ridge/high heights migrating over southeastern
Canada should limit sun intervals---however the sun should at
least make a brief appearance this weekend. Split flow regime
across the lower 48 will transition to a highly amplified pattern
by early next week across the lower 48...with a deep negatively
tilted trough evolving over the eastern 1/3rd of the Continental U.S..
The models seem to be forming a consensus on the pesky low
that refuses to be well forecast...lifting it slowly from Florida
Panhandle north-northeastward just off the East Coast sun-Monday along a low level
baroclinic zone that may not budge past the Gulf Stream as the
flow aloft turns southwesterly/parallel to the coastal front.
Increased probability of precipitation for Monday over the southeast based on multi-model/wpc
blend. Complex surface pattern with some hints at low level cad along
with warm air advection aloft via southerly flow could make for a messy mixed ptype
An intense triple point system developing on Dec 23-24 will
likely steal the headlines given its timing and large portion of
real estate that will be affected. While the details remain
unclear at this point...temperatures should be warm enough to
support rain on the front side of the system before brisk west-northwest
winds drive strong cold air advection east of the Appalachians. The timing of the
cold/occluded front will be key for precipitation transition from
rain to snow showers. As the system spins up into eastern
Canada...the strong cold air advection circulating through the Great Lakes and Ohio
Valley should lead to lake effect/upslope/wrap around snow showers
over the western alleghenies by Christmas day. A period of strong
gusty winds are highly probable as the dynamic system intensifies
shifting nwwd from New England into Ontario/Quebec.
The take home message is that a volatile period of weather will
impact the area through Christmas day with potential wind...rain
and snow impacts all on The Table. Stay tuned.
Aviation /20z Thursday through Tuesday/...
low level moisture trapped beneath inversion and northwest flow over
the eastern glaks will keep strato cumulus in place across most of
central PA through tonight. Latest model soundings point toward
predominantly MVFR ceilings/visibilities at kbfd. Elsewhere...model soundings
support ceilings around 1500ft at kjst into this evening...while
drying/downsloping flow yields progressively higher ceilings further
A trough of low pressure will push through the region tonight...perhaps
producing a period of steadier light snow at kbfd and kjst between
00z-06z Friday with visibilities in the 1-2sm range.
Friday...early am -shsn/reduced visibilities poss at kjst.
Sat-sun...no sig weather expected.
Monday...low ceilings with light rain/snow possible.