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410
FXUS61 KCTP 210353
AFDCTP

Area Forecast Discussion
National Weather Service State College PA
1053 PM EST Mon Jan 20 2020

.SYNOPSIS...
Northwest flow aloft and a large area of surface high pressure
building southeast from the Upper Mississippi Valley will
bring a lengthy string of dry days this week. Temperatures will
start out below normal before moderating back to normal on
Wednesday, then above normal to close out the work week. A
slow-moving area of low pressure will bring the potential for
snow or mixed precipitation this weekend.

&&

.NEAR TERM /UNTIL 8 AM TUESDAY MORNING/...
Clouds back into the NW and have caused the temps to rise again
there. BFD got down to 6 F before the clouds rolled in. This is
as expected. As is the mid teens at SEG and THV already. A few
flurries are falling at JHW, OLE, and likely in nrn
Warren/McKean Cos by now, too. Only a dusting of an
accumulation is expected in the NW overnight. All is well on
track.

Prev...
Temps dropping. Sky clear for all but the far SW and far NW.
Still some wind to keep things mixed up. A weak sfc trough
approaching from lower Ontario will create an increase in clouds
over the NW third/half of the area tonight. There could be a
few flurries, but opted to keep PoPs out of the forecast. The
clouds may also bump the temps back up over the NW after an
initial dip early tonight. Went below guidance for mins in the
east where wind should continue to calm down. The usual cold
spots in the valleys will get quite a bit colder than the cities
and hill tops.

Prev...
GOES-16 visible channel shows inversion heights have suppressed
shallow stratus bands over the eastern third of Lake Erie,
leaving downwind locations of the NW Mountains in full sunshine
this afternoon. Only parts of the Laurel Highlands are still
seeing any locally enhanced stratus from overlake flow tracing
from Lakes Huron and Erie. Boundary layer flow maintains similar
trajectory tonight while slackening as high pressure builds
across the Ohio Valley. A few clouds will likely drift back over
the west and northwest tonight from time to time and over the
Laurel Highlands, but the remainder of central PA is expected to
remain mostly clear to clear. With decreasing wind and snow
cover, tonight will be quite cold throughout with mins ranging
from the single digits above zero over much of northern and
central PA to 10 to 15 over the south.

&&

.SHORT TERM /8 AM TUESDAY MORNING THROUGH THURSDAY NIGHT/...
Upper ridge and elongated surface high will build southeast
on Tuesday continuing fair and cold conditions. Highs will be a
few degrees higher on Tuesday, ranging from the mid to upper 20s
north to the lower 30s southeast.

Fair weather and moderating temperatures are expected Wed and
Thu, as high pressure settles along the east coast.

&&

.LONG TERM /FRIDAY THROUGH MONDAY/...
Focus in the long term remains on the potential winter storm
this weekend. All medium range guidance shows a similar
scenario playing out, with an upper low lifting northeast from
the Miss Valley and high pressure parked north of New England.
The resulting anomalous southeasterly low level jet and plume
of Atlantic moisture overrunning a dome of cold/stable air east
of the Appalachians justifies increasing POPs Saturday. The
latest GEFS mean qpf ranges from 0.6 to 1 inch across the
forecast area by Saturday evening.

Despite the high confidence of significant precipitation,
plenty of uncertainty remains with regard to ptypes across the
area. Primary surface low is progged to weaken over the Ohio
Valley Saturday, as secondary low deepens and tracks up the Mid
Atlantic coast in classic Miller B fashion. Quicker development
of the coastal low would imply low level winds backing from SE
to NE, supplying cold air at low levels during the storm on
Saturday. This would mean more wintry precip and less rain.
Quicker development of the coastal low could also translate to
better frontogenetical forcing/banding on the NW side of the
developing low, which would translate to heavier precip and some
dynamic cooling. It will be a couple of days before we have
these answers. As always, it will be interesting to see how the
hi-res guidance handles these features as the event comes in
range.

Based on the latest ECMWF ensemble 850temps and GEFS plumes,
current forecast is for a wintry mix across much of the
forecast area Friday night into Saturday, with primarily rain
over the Lower Susq Valley and the best chance of significant
snow over the northern counties.

A deep, moist northwest flow associated with deformation band
should result in lingering light upslope snow/rain showers Sat
night into part of Monday, primarily over the Allegheny Plateau.
Do not expect any contribution from the lakes, as the air mass
behind departing storm looks too mild to support lake effect.

&&

.AVIATION /04Z TUESDAY THROUGH SATURDAY/...
Widespread VFR through tonight. MVFR conditions resume after
midnight Tuesday morning at BFD and JST as low cigs redevelop.
IFR conditions will be possible starting early Friday morning at
BFD with snow showers.

.Outlook...

Tue...Mainly dry, but still a chance of snow showers across the
northwest.

Wed-Thu...Mainly dry.

Fri-Sat...Snow/wintry mix Fri night and Saturday. Restrictions
psbl.

&&

.CTP WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$
SYNOPSIS...DeVoir/Lambert
NEAR TERM...Dangelo/DeVoir
SHORT TERM...DeVoir/Lambert
LONG TERM...Fitzgerald/Colbert
AVIATION...DeVoir/Banghoff