Area Forecast Discussion
Issued by NWS State College, PA

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FXUS61 KCTP 222153

Area Forecast Discussion
National Weather Service State College PA
553 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

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.


Just some mid and high clouds on this nice late fall
afternoon. 21Z TAF set sent.

Will look at the low cld situation more later, when I do the

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.


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.

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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