Scientific Forecaster Discussion
fxus61 kctp 190323
Area forecast discussion
National Weather Service State College PA
1023 PM EST Mon Nov 18 2019
low pressure will move northward off the coast and an upper
level trough will pass overhead tonight. Weak high pressure in
the middle of the week will keep it seasonable and mainly dry
Wed. A cold front will arrive Friday morning, but temperatures
will not drop much below normal for the weekend.
Near term /until 6 am Tuesday morning/...
forecast in good shape late this evening as upper low pressure
centered over WV/Maryland panhandles and east-southeast boundary layer flow is
focusing moisture and light showers/dz over my southeast
counties. A light westerly upslope flow may also pool low level
moisture over the northwest mtns overnight, with some local drizzle in
the morning. Some areas may be at or below freezing for some of
the area, mainly the alleghenies overnight. So, will continue
to mention patchy dz/fzdz...but confidence is still quite low on
any particular location getting below freezing. Plus, Road
temps may remain at or above freezing over most places, lessening the
potential impacts of the light glaze which was/is possible.
Short term /6 am Tuesday morning through 6 PM Tuesday/...
westerly flow is rather anticyclonic for the daytime tues. This
usually keeps any lake effect to a minimum. Flow off the lake
is pretty weak/slow. However, clouds look to darken the day for
much of the County Warning Area as low crud develops in the moist upslope. The
most likely places to have the low clouds and some dz are the
alleghenies. Temps will be marginal around sunrise for patchy
fzdz. But, solar warming and neutral temp advection should allow
for the end of any fzdz threat during the mid morning.
Clouds stay stubborn in the northwest half/two-thirds. Have stayed a
bit below blended guidance maxes. Temps across the southeast could
still get close to 50f. But, about half the area won't get to
Long term /Tuesday night through Monday/...
a few light snow showers or perhaps a bit of lingering drizzle
or freezing drizzle remains possible into Tuesday night across
the northern and western Highlands. Wednesday should see
improving conditions, as high pressure builds in from the Ohio
Valley. Temperatures will remain a few degrees below normal for
High pressure will slide to our east on Thursday, allowing a
southerly flow to develop and draw milder air into the region.
High temperatures should be a few to several degrees milder
than what we see Wednesday, with areas along and south of the
Route 322 corridor topping 50 degrees.
A cold front will approach Thursday night into Friday, bringing
a chance of rain showers into the area. However, this is where
the models begin to diverge.
The 12z European model (ecmwf) stalls the cold front near the Mason-Dixon line
Friday night and then brings a surge of moisture up the Ohio
Valley this weekend in association with a deepening area of low
pressure. This solution would spread a chilly rain back into
central PA Fri night into Saturday. The 12z GFS, on the other
hand, is more progressive with the cold front. It brings in a
stronger push of chilly air and pushes the cold front farther
to our south. This solution would shove the moisture and
developing low pressure well to our south over the weekend.
The multi-member 12z gefs hints at the possibility of the
moisture making it back into central PA on Saturday. This,
combined with the tendency for the operational GFS to be a
little too progressive with systems so far this fall, led ME to
paint chc to slgt chc pops over central PA Friday night through
Saturday. Right now, it looks like most of what would fall
would be rain, but considerable uncertainty remains.
Aviation /04z Tuesday through Saturday/...
a weak area of low pressure will lift across southeast PA late
this evening, bringing a period of light rain to that part of
the state. Otherwise, it looks like a dry night across the
region. The main concern will be developing low cigs and fog
overnight, caused by a nearly calm wind and resulting
radiational cooling. A blend of ensemble and latest operational
model runs indicate IFR conditions will be likely across
northern PA and will remain quite unlikely over the Laurel
Highlands, where a southerly breeze should limit radiational
cooling. Elsewhere, there is the possibility of late night IFR
conditions, but the forecast remains uncertain and revolves
around how fast mid level cloudiness exits the area.
Expect improving conditions Tuesday across the eastern half of
the state, as a drier westerly flow develops in wake of
departing low pressure. Latest sref probability charts indicate
VFR conditions will be likely across this area by midday.
However, model soundings indicate residual low level moisture
ascending the Appalachians will result in lingering stratus
across the northwest mountains (kbfd) and developing stratus
over the Laurel Highlands (kjst).
Wed...am low cigs possible west mtns.
Thu...patchy am fog possible.
Fri...am low cigs/showers possible west mtns.
Sat...rain/low cigs possible.