Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 220540
AFDCTP

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

.SYNOPSIS...
A large area of high pressure centered over Pennsylvania and
eastern Virginia this afternoon will drift east of the area
by late Monday. This high will give us a spectacular Autumn
conditions for Sunday and much of Monday, to enjoy the fall
foliage.

A high-amplitude and cold upper trough will become carved out
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 for a narrow band of gusty thunderstorms
to 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 Northwest Mountains and Laurel Highlands
of Pennsylvania.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
No real change to the late evening fcst.

Patchy river valley fog is at a minimum this morning compared
to recent days. Dewpoints similar to last evening, so hard to
see much in the way of fog tonight.

Did lower temperatures a degree or so, given low dewpoints
and light winds. Still several bands of high clouds to the
west, but clouds should thin some late.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
Sunday will be a near carbon copy of Saturday 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 teens.

Did up temperatures by 2 to 3 degrees, hard to see it staying
cooler than today, given slight increase in wind. Still expect
some high clouds, but dewpoints not fcst to climb much before
dark. Also flow is not like last week, where we had days of
high dewpoints with east to southeast winds, and strong cold
air damming.

Thus expecting a nice Sunday, enjoy.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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 a long plume of moisture
into the state from the south.

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

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.

&&

.AVIATION /06Z SUNDAY THROUGH THURSDAY/...
Patchy fog is possible early this morning across the eastern
1/3 of the airspace - otherwise VFR conditions and light winds
will continue to dominate the aviation forecast into tonight.
Guidance is indicating risk for MVFR/IFR conditions developing
late tonight into early Monday morning across the eastern
airspace and will address this with the 22/12z scheduled TAF
issuance.

Outlook...

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.

&&

.CLIMATE...
Month-to-date, October 2017 was the warmest October on record
at Harrisburg and Williamsport several days ago.

&&

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

&&

$$
SYNOPSIS...Martin
NEAR TERM...Martin
SHORT TERM...Martin
LONG TERM...Lambert/Tyburski
AVIATION...Fitzgerald/Steinbugl
CLIMATE...Steinbugl



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