Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 221349

Area Forecast Discussion
National Weather Service State College PA
949 AM EDT Sun Oct 22 2017

A large area of high pressure centered off the New Jersey coast will
bring spectacular Autumn conditions today through much of Monday, to
enjoy the near peak color of the fall foliage.

A high-amplitude and deepening, cold upper trough will become
located across the eastern U.S. during the Wednesday and
Thursday timeframe. This weather feature will be preceded and
accompanied by rain that could be heavy at times late Monday
into Tuesday. There is also a chance that a narrow band of
gusty thunderstorms will develop and push east across the state
along a cold front during the day Tuesday.

Brisk and colder weather will follow for Wednesday afternoon
through Thursday with the likelihood of the first snowflakes of
the season across the Northern and Western Mountains of



Cooler air this morning will stifle temperatures a little today.
However today will be a near carbon copy of yesterday temp-
wise, though the southerly breeze will likely increase by 5 kts
or so, into the 8-10 kt range with gusts into the mid- upper

Variable amounts and thickness of high clouds
(cirrus/cirrostratus) will also spread across the Commonwealth
by this afternoon, and will persist through tonight. The high
clouds today will likely dim the sun at times.

Max temps today will be very uniform (71-75F), within a degree
or two of Saturday`s high.


Areas of stratus will advect north and westward beneath the
rather widespread cirrostratus layer expected tonight.

Thanks to the cloud cover, low temps tonight will be in the
low-mid 50s, or a good 10-15F above normal lows.

An upper level trough low swinging through the upper midwest
will absorb a closed upper low over the lower Mississippi valley
during the day Monday. This will bring an extensive plume of
moisture into the state from the south.

The south to Serly llvl flow will freshen by about 10 kts during
the day Monday and bring with it areas of low clouds
(stratus/Stratocu) and perhaps some patchy drizzle across the
central third of the state.

Max temps Monday should be about 3-4 F lower than those of
today for everyone except those in the Lower Susq Valley.


Models have converged to indicate the center of the significant
rainfall event occurring later Monday night through Tuesday
evening when widespread rainfall amounts of 1-1.5 inches is

As the cold front works slowly east across the Commonwealth
Tuesday into Tuesday evening, SFC-850 mb LIs go slightly
negative across parts of southcentral PA and the Susquehanna
Valley. In addition to the expansive shield of moderate to
briefly heavy rainfall rates, the pattern appears favorable for
a Narrow Cold Frontal Rainband - NCFRB (with brief gusty winds)
to push through as well.

By Thursday, 850 mb temps drop below zero which will bring a
relatively chilly day with scattered rain showers which may mix
with a snowflake or two over the higher elevations. However,
this cooler stretch will be short lived as heights and 850 temps
rise quickly into next weekend.


Patchy fog in the valleys will dissipate by 14Z with little to
no terminal impacts. VFR conditions will continue to dominate
the aviation forecast into tonight. Guidance indicates risk for
low clouds and fog developing late tonight into early Monday
morning across the eastern 1/3 of the airspace - and have added
MVFR/IFR restrictions starting at 23/06z. Not sure how far west
the low clouds will reach so hedged low cig potential at
KUNV/KAOO with SCT025 cloud group.


Mon...AM low cigs/fog possible eastern 1/3. Showers advancing
into the airspace Monday night with lowering cigs/vis and LLWS.

Tue...LLWS/gusty/heavy showers in the morning. Sharp FROPA and
windshift. Improving conditions by afternoon.

Wed-Thu...Sct showers and low cigs possible KBFD/KJST.


Month-to-date, October 2017 remains the warmest October on
record at Harrisburg and Williamsport. Despite very warm days,
seasonably cool nights and calender length has been putting a
dent in the avg. monthly temperature at both sites. The top
spot is in jeopardy given upcoming pattern change/cool down
expected by midweek.




NEAR TERM...Lambert/Ceru
SHORT TERM...Lambert
LONG TERM...Lambert/Tyburski
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