Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 222355

Area Forecast Discussion
National Weather Service State College PA
755 PM EDT Sun Oct 22 2017

Low pressure over the Mississippi Valley will track northward
through the Great Lakes late Monday and Tuesday. A trailing
cold front will push through Pennsylvania Monday night into
early Tuesday. An upper level trough will then swing through
Pennsylvania Wednesday and Thursday.


Ridging at the surface and aloft will remain along the east
coast tonight, ensuring a continuation of fair weather across
the area. A southerly breeze, combined with a thin cirrus
shield, should result in a milder night than those recently.
A blend of latest model guidance supports overnight lows
between 50-55F.

Although there should be enough of a breeze to preclude fog
issues over the bulk of central Pa, a weaker gradient across
southeast Pa could lead to some fog across the southeast part
of the forecast area early Monday morning.


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.
Short to mid range models continue to narrow in on the
timing of the approaching system. 12Z GEFS and NAM are in
fair agreement on precipitation reaching Western PA and the
Alleghenies late tomorrow afternoon.


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 south central 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.

Another chance for precipitation will arrive at the end of the
period when a cold front is anticipated next Sunday, bringing
rain showers to the region.


Expect most of the night to be VFR. Model data shows
lower visibilities and CIGS late, which may linger into
late morning or early afternoon on Monday. Not sure it
will occur, as no real cold air in place, but slight
southeast flow late, with leading edge of higher dewpoints
working in, left fcst close to what the 18Z package had.

Main change was to bring in lower conditions a tad faster in
some spots, and linger it a hour or so later in some spots.

Expect most of the day to be dry. Some showers possible
late, just have showers in far west around sunset.

LLWS possible far west toward sunset, so have it in for
BFD and JST.

Earlier discussion below.

Guidance continues to show risk for low clouds and fog
developing late tonight into early Monday morning across the
eastern 1/3 of the airspace - and have increased and spread
MVFR/IFR restrictions through the eastern and central TAF sites.
Have kept restrictions until around 14Z. LLWS is possible at
JST/AOO and BFD but it is marginal as strongest low level jet is
above 2KFT. So have left it out of the TAFs for now.


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.

Fri...Mainly VFR.


Month-to-date, October 2017 remains the 2nd and 3rd warmest
on record at Williamsport and Harrisburg respectively.




NEAR TERM...Fitzgerald
SHORT TERM...Lambert
LONG TERM...Lambert/Gartner
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