Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 220042 AFDCTP Area Forecast Discussion National Weather Service State College PA 842 PM EDT Sat Oct 21 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 SUNDAY MORNING/... 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 SUNDAY MORNING THROUGH 6 PM SUNDAY/... 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 /SUNDAY 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 /00Z SUNDAY THROUGH THURSDAY/... High pressure over Pennsylvania will ensure widespread VFR conditions and light wind through Sunday. A few isolated pockets of fog are possible early Sunday morning, but the odds are low that any central Pa airfields will be affected. Outlook... Mon...AM low cigs/fog possible. Tue...Early AM showers/low cigs/LLWS possible. Wed...Evening showers/low cigs possible BFD/JST. Thu...AM showers/low cigs possible BFD/JST. && .CLIMATE... Month-to-date, October 2017 was the warmest October on record at Harrisburg and Williamsport several days ago. However, cooler lows of the past few days, compared to last weekend, have resulted in Oct 2017 being just short of 1st place now, by about an degree. October 2007 warmest. Still about 11 days to go. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...DeVoir/Martin NEAR TERM...DeVoir/Martin SHORT TERM...DeVoir/Martin LONG TERM...Lambert/Tyburski AVIATION...Fitzgerald CLIMATE...

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