Scientific Forecaster Discussion
Area forecast discussion
National Weather Service State College PA
903 PM EDT sun Mar 9 2014
high pressure extending eastward from the Ohio Valley will sink
southward toward the central Gulf Coast by Monday morning. Two
clipper type systems tracking rapidly downstream from western
Canada will move through upstate New York and northern New England
Monday and Tuesday. A late-winter storm system will impact the
area on Wednesday...followed by cold and blustery conditions for
Near term /until 6 am Monday morning/...
varying amounts of middle and high cloud will continue to stream
across PA overnight...while surface ridge axis slides east across the
region. Freshening southwest breeze west of the ridge axis will advect
milder air in aloft and result in overnight temperatures nearly steady
across the west or perhaps even a rise towards morning. It will be
different across the east which remains under the tranquil ridge
axis longer. Sheltered valleys across the middle to lower
Susquehanna River valley will be coldest... generally in the middle
to upper 20s.
Short term /6 am Monday morning through Monday night/...
small scale shortwave disturbance will shift eastward from Lake Huron
across southern Ontario and into upstate New York early Monday. Model
consensus continues to support some scattered light snow/rain showers
early tomorrow/prior to 18z mainly north of i80. The afternoon should
feature improving conds with temperatures warming nicely into the low-
middle 40s north to low-middle 50s south. Depending on cloud
trends...could see warmer maximum temperatures especially over southern PA given
downslope flow. Dry/quiet weather continues into Monday night with relatively
mild lows ranging from around 30f in the north to near 40f in the
Long term /Tuesday through Sunday/...
models in quite good agreement on overall pattern into the
weekend...providing a higher confidence forecast on main weather
Clipper system slides by Monday night...sagging a weak frontal
boundary southward across County Warning Area. But low level flow behind it
running parallel to isotherms will keep milder temperatures in place
through a fairly nondescript day. Middle-high clouds will begin to
increase and thicken through the day as approaching storm system
gets organized over the Southern Plains.
This system...currently an upper wave off the West Coast of
Canada...will drop southeast across the northwest U.S and through The Rockies.
As trough deepens...surface low will form by the time it drops
into the Southern Plains /KS-OK/. A second wave dropping out of
the Canadian rockies will further sharpen and deepen the trough as
it digs toward the Ohio Valley by Wednesday...dragging the surface low
eastward through the tenn valley...tracking just south of the
Mason/Dixon line and then toward New England. Again...latest model
guidance very much in step with each other...with GFS speed just a
shade faster than the European model (ecmwf). Both indicating a slightly deeper low
than previous runs. Even 850mb temperature fields beginning to match better
in 12z runs in both initial placement and progression of colder
air across County Warning Area on back end of storm.
This set up has US starting off rather mild...making the initial
precipitation type likely to be rain in all but far northern counties.
Light precipitation will work into the northwest Tuesday night...with only minor
impacts. The heaviest precipitation arrives during the day Wednesday...with the
coldest air remaining confined to mainly northern mountains through the
first half of the day...then as the upper trough and surface low
begin to deepen and move east...colder air will be dragged down
from the north bringing about a changeover to snow/sleet further
south into most areas but extreme southeast. At this range though...its
still a somewhat irresponsible call to draw specific lines...but
it is becoming more likely that northwestern into parts of
central mountains stand a high probability of receiving a fairly
prolonged period of moderate to even heavy snow as the cold air
sweeps in Wednesday into Wednesday evening. With inherant uncertainty in
the fine details and the fact that this storm is still in period 6
of the forecast...have used the hazardous weather outlook /hwoctp/
product to highlight the midweek wintry potential.
Quite cold air /around -20c/ drives in behind the exiting low Wednesday
night into Thursday...with by far the coldest day of the week in store.
Temperatures will again fall to well below normal...with highs below
freezing in the southeast...and struggling to approach 20f across
the northern and western higher terrain. Combined with a stiff
breeze...wind chills below zero will be likely across northwest half of
County Warning Area for a decent portion of the day.
The well-below normal cold will be short-lived though...as temperatures
rebound decently Friday into Sat...bouncing back to near seasonal
normals. However this Winters defining feature...the persistent
West Coast ridge...again re-establishes itself heading into next
week. This will allow for cooler air to filter back into the
region in persistent northwest flow over PA...keeping temperatures near or
slightly below normal and preventing any kind of significant warm
up. It may also set the stage for another potential low pressure
system in the Sun night-Monday night time frame.
Aviation /01z Monday through Friday/...
high pressure ridge over Pennsylvania will provide a high
confidence of VFR flying conds tonight across central PA. Biggest
aviation concern will be the possibility of low level wind shear developing in
response to increasing west winds aloft. Latest BUFKIT soundings
suggest low level wind shear criteria will likely be met between 05z-13z in the
central valleys...including kaoo/kunv/kipt. Elsewhere...low level wind shear looks
marginal so decided not to mention in tafs.
A weak low/upper level disturbance will track southeastward across the area
late Monday morning. This feature should support isolated-scattered -shsn over
the northern airspace with MVFR ceilings possible late am at kbfd. Low VFR
ceilings around 4kft are likely across the northern half of the state
into the afternoon...with a low chance of marginal restrictions at kbfd.
Tuesday...am low ceilings poss West Mountains
Wednesday...MVFR-IFR restrictions likely in rain or snow. Windy late.
Thursday...strong/gusty north-northwest winds possible.
Friday...no sig weather expected.
long term...la corte/rxr