Scientific Forecaster Discussion
fxus61 kctp 180632
Area forecast discussion
National Weather Service State College PA
132 am EST Mon Nov 18 2019
a storm system will move slowly up the East Coast through
Tuesday. An upper level trough will swing in from the west
Monday night and Tuesday. The middle of the week will hold a Few
Lake effect snow showers, but will be mainly dry and seasonable.
A fast-moving cold front will arrive Friday morning.
Near term /until 6 am this morning/...
a few clear spots, with some cooling, but most of the area is
cloudy as of 10 PM.
Updated the fcst as of 8 PM. Not much left on radar. Some very
tiny east, west bands on the lwx radar.
Main change to the fcst was to edge temperatures up a few
degrees, given cloud cover. Not expecting much change in
Late afternoon discussion below.
Very thin layer of low clds resulting in small convective type
snow showers at times earlier this afternoon, too brief to
accumulate anything. Most of the activity on the radar is gone
now, did extend mention of flurries out another hour until 00z.
As mentioned below, a little strange, no seeder layer to aid
formation of snow flurries.
Earlier discussion below.
Thin lower clouds (bases around 3kft) must be in the Sweet spot
for generating dendrites because they are generating flurries as
they stream northward. No seeder layer to help this happen, as
the high clouds are to the southeast of the County Warning Area. Interesting and
challenging. The working theory is that the clouds will
stratify as we lose the mixing/instability and this should kill
off any flurries around or even before sunset. The clouds should
also thicken up through the night. By sunrise, a few sprinkles
or patches of dz/zl are possible in the far eastern zones.
Diurnal drop should be minimal due to the clouds in most places.
Mins will be in the m20s and l30s.
Short term /6 am this morning through 6 PM Tuesday/...
adjusted temperatures and dewpoints some for Monday, but very
Thinking was that the airmass would continue to slowly warm
Earlier discussion below.
Off-shore low will move northward and upper trough will approach
from the west thru the period. Forecast continues steady-state
for the most part, with many models spitting out a hundredth or
two of precip on Monday and the first part of Monday night for
the far eastern zones. Much of the time, the temps and vertical
profile temps will be mild enough for only ra/dz. The threat for
some mixed precip is there, but confidence is very low in
p-type, and even occurrence. If it does fall, the quantitative precipitation forecast is pretty
The European model (ecmwf) does generate quite a good bullseye of 0.5"+ of quantitative precipitation forecast
over the Poconos (mainly to our east, but incl eastern
Schuylkill co) early Monday night. The wet bulb temps are
marginal for wet snow over the higher elevations. Have mentioned
minimal accums and a light glaze of ice in that period for
mainly Sullivan and Schuylkill counties. But, confidence is very
low, so no headlines for this period, either.
Long term /Tuesday night through Sunday/...
*not as cold but below-average temperature bias continues
*potential for light wintry precip off and on this coming week
Looking to the week ahead, expect temperatures to gradually
trend milder but with a below-normal bias. Thursday looks like
the only day that most locales slip just above average, with the
southeast potentially ending up a bit above normal on Fri as well. The
latest long term temperature outlooks favor below average
readings through the end of the month.
There remains some variability in the model guidance (low
confidence forecast) concerning the precipitation type and
occurrence this week.
Tuesday looking chilly as upper low associated with exiting
storm along coast slides through. Another northern stream
disturbance/upper level low or clipper moves across PA Tuesday
night into Wednesday bringing chance for rain and snow showers
over the northwest. A brief period of lake effect/upslope
precipitation on the back end of this is possible hence low pops
Next wave deepens as it crosses the Great Lakes Thu and Fri.
Looks like the precip should hold off late enough Thu to miss
shot at a light wintry mix at onset, with precip type being
primarily rain as we remain on east side of this system.
On Thursday night some snow may work in over the higher terrain
of the NW, and across the northwest half on Fri as precip shield
retreats back toward the northwest before ending. Another brief period
of lake effect is possible on the back side of this system by
Sat looks pretty quiet, but yet another weak system sneaks in by
Sat night/Sunday with potential for a wintry mix.
Aviation /07z Monday through Friday/...
06z observations confirm the latest satellite that shows the
streaming bands of clouds moving over the region as moist
easterly flow off of the Atlantic Ocean will continue to
produce stratus across central PA through Monday.
Bfd and aoo have already gone IFR with lowering cigs at the
other taf sites. MVFR has formed or lower at all taf sites
except lns. Temperatures are warmer then last night with only a
slight cooling in the boundary layer. That should cause cigs to
lower a bit overnight. Model soundings and sref probability
charts suggest IFR cigs are likely late tonight, primarily over
the high terrain of the alleghenies from kbfd south through
Expect improving conditions Monday afternoon across central and
western PA, where low level moisture should mix out. Ensemble
output suggests VFR conditions will become likely over this part
of the state by late in the day, while MVFR cigs linger over
Tue...am fog possible. Evening low cigs possible northwest mtns.
Wed...am low cigs possible west mtns.
Thu...patchy am fog possible.
Fri...early am low cigs/showers possible west mtns.