Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 211323

Area Forecast Discussion
National Weather Service State College PA
923 AM EDT Sat Oct 21 2017

A large area of high pressure centered over Pennsylvania and
eastern Virginia this morning will drift slowly to the east over
the next few days, providing us with a spectacular Autumn
weekend to enjoy the fall foliage that will be near its peak

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, 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.


Patchy river valley fog is at a minimum this morning compared to
recent days. This will dissipate shortly. Aside from a gradual
increase in cirrus clouds during the late morning and afternoon
hours today, another fabulous fall day is on tap under a large
area of high pressure. Afternoon high temperatures in the low to
mid 70s will be 12 to 17 degrees above normal, with the biggest
departures occurring across the Northern and Western Mountains.
A few spots across southern PA could see the temp top off
around 77F.


More extensive high clouds will likely spread across the region
tonight, leading to notably milder temps in the 40s to near
50F. The cloud cover will also prevent complete decoupling of
the boundary layer, allowing for a light south to southeast
breeze of 3-6 kts.

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.


Stand-alone shortwave over Gulf States Mon will be overtaken by
a significant digging northern stream trough that will
eventually take on a slightly negative tilt early next week as
it moves from the upper midwest and Miss Valley to the
Appalachian Mtns and Carolina Coast.

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 acrs parts of Scent PA and the Susq 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

Then we`ll almost certainly transition to a period of below
normal temperatures for the second half of the week ahead as
flow shifts to the NW as result of deepening upper trough
swinging pushing east across the area. A fair amount of clouds
will occur across the NW half of CWA Wednesday - Thursday with
scattered showers of rain/snow also poss across the higher
terrain of northern PA...and the Laurels beneath the cold core
of the upper trough.

There are indications of rising heights/milder weather
returning again for the entire eastern conus toward the end of
the month.


High pressure over Pennsylvania will ensure VFR conditions and
light wind through tonight with a gradual increase in high


Sun...Patchy AM valley fog possible mainly southeast terminals.

Mon...VFR. Showers advancing into the airspace Monday night-AM

Tue...LLWS. Sharp FROPA/wind shift. Gusty showers with locally
heavy downpours possible. Breezy but improving Tues night.

Wed...Rain showers/low cigs possible western 1/2.


Month-to-date, October 2017 is the warmest October on record at
Harrisburg and Williamsport.




NEAR TERM...DeVoir/Lambert
SHORT TERM...Lambert
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