Area Forecast Discussion
Issued by NWS State College, PA
FXUS61 KCTP 241608
Area Forecast Discussion
National Weather Service State College PA
1208 PM EDT Sat Sep 24 2016
A large area of high pressure near James Bay Canada will drift
south and becoming centered over the northeastern states on Sunday.
Expect fair weather with seasonably cool temperatures through this
weekend. A cold front will push through early in the upcoming week
and should help generate some rain late Monday into early
Tuesday. Dry weather will return for the rest of next week.
.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Sharp clearing line near the Interstate 80 corridor this midday
hour will continue to progress steadily south during the
afternoon...reaching the southern tier of PA between 19Z-21Z. The
last location likely to see the clearing should be the Laurel
Highlands where a bkn strato cu deck could hold tough through
early this evening.
Mdt near sfc cold advection will battle the still relatively high
late Sep sun angle and associated warming...while notably stronger
cold advection at 850 mb and a Lake Ontario/850 mb delta T
approaching 20c helps to create plenty of strato cu streamers off
Lake Ontario...which will spread over the Northern Mtns of PA at
times this afternoon.
Max temps this afternoon should be 10-15F cooler than yesterday`s
lofty temps. But, they will still be just at...or slightly above
normal for the date.
.SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/...
Skies will become clear in most places by early this evening and
PWATs will be below normal under the subsidence of the advancing
high pressure bubble. This airmass change will make it really feel
like autumn as temps drop off into the m-u30s in the northern
mountains, and 40s elsewhere. With the prolonged period of very
much above normal temperatures, this will be quite a shock to
some. There could be just a little bit of the north wind left
tonight and a few wisps of high clouds. But otherwise, these
conditions are very good for frost. It is also difficult to shake
the idea of abnormal warmth from the forecast, as well. Forecaster
bias tells me that it may not get quite that cold when temps got
5F higher than forecast at IPT yesterday. But, it is a new
airmass. This may be a case where the current temp anomaly clouds
forecaster judgment. Will mention patchy frost for now and stay
barely on the high side of the MOS temp guidance for mins.
Dayshift may have more certainty on frost formation. But the cold
air draining into the river valleys will then set up a battle
between the river valley fog and frost. These two phenomena are
Sunday should be stellar with low dewpoints, few clouds after the
valley fog lifts, and temperatures almost normal. Some high clouds
will slide down from the NW Sunday night. These may have a tiny
effect on temps, but there may be a little bit of an east wind.
Guidance says that it should be quite a bit milder in the west
Sunday night vs. Sat night. Will stay close to these numbers.
.LONG TERM /MONDAY THROUGH FRIDAY/...
Clouds increase Monday ahead of significant cold front headed our
way. Recent guidance has hurried up with the timing of the front.
Have adjusted things by 3-6 hours faster. This then puts the
timing of showers during the afternoon/evening in the west. Will
add a slight chc thunder in there due to the peak heating/lower
stability possible with this timing. Certainty of rainfall for
most of the area has climbed into the 60-70pct range. This will
be much needed rainfall, centered on Monday Night. The front
should be through by Tuesday morning. Will linger only chc POPs in
the far SE and keep them in the far NW for lake-effect and/or
cool air aloft instability showers for mid-week. Temps should stay
very normal for the balance of the week - but the dryness returns
for a long period.
.AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
Post-frontal lower MVFR ceilings are confined to the southern PA
Airfields attm...and will be improving to vfr during the mid to
late afternoon hours...with mainly VFR conditions elsewhere.
Lake Effect cloud streamers in the MVFR range will be pushed well
south from Lake Ontario will drift into the northern mtns of PA
and impact KBFD at times through 21z.
VFR with clear skies and light winds overnight could lead to some
patchy fog by Sunday morning.
Mon...PM showers/Tstms with reductions possible.
Tue-Wed...No sig wx expected.