Area Forecast Discussion
Issued by NWS State College, PA-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
FXUS61 KCTP 242002
Area Forecast Discussion
National Weather Service State College PA
402 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 the
rest of this weekend. A cold front will push through the region
late Monday and Monday night and should help generate much needed
rainfall on the order of a few to several tenths of an inch. Dry
weather will return for the rest of next week.
.NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
Sharp clearing line has pressed south from Interstate 80 to the
route 22/322 corridor early this afternoon and will reach the
southern tier counties 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. However...the amount of subsidence and deep dry air
across the nrn mtns of PA should keep skies there clear to partly
18Z Temps in the lower 60s across the nrn and western mtns...and
u60s to lower 70s in the southern valleys are nearing their max
values for the afternoon...which will be near to slightly above
normal for the date. Will need to back off on fcst highs across
the Laurels considering the persistent bkn-ovc cloud cover there.
Skies will become clear in most places by early this evening and
PWATs will be below normal under the subsidence of the
approaching, sprawling 1028mb area of high pressure bubble.
A true taste of autumn will be in the air tonight as temps drop
off into the m-u30s in the northern mountains, and 40s elsewhere.
Expect at least patchy frost throughout the rural valleys of the
north. With the prolonged period of very much above normal
temperatures, this will be quite a shock to some.
Light north winds tonight should go light and variable in the
deeper valleys between 06Z-13Z Sunday. This light wind combined
with clear skies and a greater than 20F air/water temp
diff will likely lead to development of fog (that could become
locally dense). The extent and vsby associated with the fog are
still somewhat in question. 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 rarely coincident.
.SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
Sunday should be stellar with low dewpoints, spectacular
visibility, and just a few clouds after the valley fog lifts.
After the chilly start, temperatures will rebound to around
Some high clouds will slide down from the NW Sunday night. These
could have just a minor effect on temps. 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 SATURDAY/...
-- Changed Discussion --Clouds increase Monday ahead of significant cold front headed our
way. Recent guidance continues to speed up the timing of the
front. Have adjusted things accordingly and split up the wx grids.
This then puts the timing of showers during the afternoon/evening
in the west. Showers should be out ahead, however given the
instability, diurnal heating have put in thunder 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, with highest amounts Monday Night. Based on latest data
have increased QPF amounts, especially where thunder is possible.
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, though
cooler. There will be another extended period of dryness.
-- End Changed Discussion -- &&
.AVIATION /20Z SATURDAY THROUGH THURSDAY/...
Lingering post-frontal MVFR ceilings are confined to our 4
southern PA Airfields attm...and will be improving to vfr during
the late afternoon/early evening hours...with VFR conditions
Lake Effect cloud streamers in the MVFR range should erode late
this afternoon/early this evening in the very deep dry air before
spilling into the nrn mtns of PA.
VFR with clear skies and light winds overnight could lead to some
patchy dense valley fog during the mid morning hours of
Sunday...mainly at KBFD and KIPT with less confidence at KUNV.
Sunday...Expect widespread VFR after 14Z, which will continue
through Sunday night.
Mon...PM showers/Tstms with reductions possible.
Tue-Wed...No sig wx expected.