Scientific Forecaster Discussion
fxus61 kctp 202041
Area forecast discussion
National Weather Service State College PA
341 PM EST Sat Jan 20 2018
moisture will creep into the western mountains tonight.
Temperatures will rise above normal today and stay there through
mid-week. A cold front will move through the area later Monday
night and early Tuesday.
Near term /until midnight tonight/...
quite a nice day underway compared to recent days. The sun is a
little filtered by the high clouds in the southeast and temps are just
a few degs slow in meeting the fcst maxes. However, the wind is
keeping things well-mixed and very mild. The mixing is only up
to about 2-2.5kft. The loss of sunlight/heating will result in
the eastern areas decoupling again, and they will get just as
cool as the nrn mtns later tonight.
Short term /midnight through 6 PM Sunday/...
the risk of ice jam flooding will continue over the weekend and
into early next week. See the Hydro section for more details.
Clouds do creep in from the SW tonight, but it seems like the
models are very aggressive in dropping the wrn counties into the
crud. The closest low clouds are clouds around 3kft over far srn
WV and ern Kentucky. Nighttime stratification should assist the
upslope in making the forecast low clouds appear. Will, however,
be less aggressive with the influx of clouds. Will continue to
mention the possibility of fzdz in the grids. But the temps may
be just above freezing as the clouds and drizzle materialize. As
the clouds arrive I would expect the temps to go up a bit, too.
So, no advy at this point. Will allow later shifts to futher
assess the situation.
By sunrise, about half of the area should be overcast and clouds
will creep eastward, but mixing will keep the bases higher to
the east of the alleghenies. No need for pops until the
afternoon when continued influx of moisture and upslope into the
eastern ridges makes it possible for a drip or two to fall
there. Maxes will likely be challenged by the clouds. Will keep
them a little lower than guid.
Long term /Sunday night through Saturday/...
another January thaw will bring a period of relatively mild
weather to central PA through early next week. Temperatures are
not expected to be as warm as the previous thaw (late last
week), but departures should reach +10 to +15 degrees above
average for mid to late January, peaking Monday in the northwest and
Mon into tues in the southeast. The progressive pattern will keep the
cool down during the middle/late part of next week rather brief
before temperatures moderate/trend warmer into next weekend.
The start of warm advection Sunday night and Monday ahead of a
strengthening Mississippi Valley/Great Lakes cyclone will
impinge on a retreating thermal gradient between I-80 and I-90.
Forecast soundings indicate moisture will be rather shallow
initially with areas of light rain confined mainly to the
western and northern parts of the area. Elsewhere expect low
clouds to develop with pockets of drizzle/mist and fog.
As the cyclone approaches, Monday will see the light showers
retreat to the north with the warm front (thermal boundary).
The most likely period for widespread rain is Monday night into
early Tuesday along/ahead of south-southwesterly low level jet axis and
cold/occluded front. A weak secondary low may form in the Lee
of the Appalachians and support a period of enhanced rainfall
over the eastern 1/2 of PA Tuesday morning. At this time, the
total rainfall forecast for early next week does not appear to
be as heavy as Jan. 11-12.
Winds look rather blustery from later Tuesday into Wednesday on
the backside of the low pressure system as colder air filters
back in. Snow showers are likely downwind of Lake Erie into Wed
night. Dry wx with moderating temperatures Thu-Fri under high
pressure. Some showers may sneak into the northwest Sat as weaker low
pressure system lifts across the Great Lakes, with better
chances for rain with another low on Sunday.
Aviation /20z Saturday through Thursday/...
a MVFR stratocu/stratus deck should form or move into the
western zones tonight. This deck will become IFR at bfd and jst,
and there will likely be some --ra and/or dz at both sites.
Clouds could lower to IFR unv and aoo, but those latter two
airfields will have a bit of a downslope and this should help to
keep it dry and just MVFR at unv/aoo/ipt.
The gusty wind will diminish with loss of heating and as the low
to our north slides to the NE.
As the moisture pools and builds over the area, the threat of dz
could spread into the Poconos. Scattered rain showers also possible over the
nrn mtns on Sunday.
Sun PM...scattered rain showers - mainly in the north. Otherwise MVFR S and
Mon...reduced flight categories with rain showers associated
with an approaching cold front - mainly north. Improvement expected
from S-north thru the day.
Tue...VFR W/scattered MVFR in rain showers.
Tues PM-Wed...IFR shsn northwest. MVFR/VFR southeast.
Thurs...no sig wx.
main concern is watching water levels rise on susq downstream on
Harrisburg. Marietta gage /mrtp1/ continues its slow rise as ice
builds up downstream. Gage above action stage and there is some
minor flood concerns in Wrightsville ongoing. The Flood Watch
for this area has been extended through the weekend, set to
expire Monday afternoon. With milder temperatures there is
potential for ice movement, as well as slow ice
deterioration/thinning with time. All areas near rivers and
streams that have significant ice buildup should monitor water
levels closely for the next several days.
Flood Watch through Monday afternoon for paz065-066.