Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 211910 AFDCTP Area Forecast Discussion National Weather Service State College PA 310 PM EDT Sat Oct 21 2017 .SYNOPSIS... 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 color. 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 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. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... 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. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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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.
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&& .AVIATION /19Z SATURDAY THROUGH THURSDAY/... High pressure over Pennsylvania will ensure VFR conditions and light wind through tonight with a gradual increase in high clouds. Outlook... Sun...Patchy AM valley fog possible mainly southeast terminals. Mon...VFR. Showers advancing into the airspace Monday night-AM Tuesday. 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. && .CLIMATE... Month-to-date, October 2017 is the warmest October on record at Harrisburg and Williamsport. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...DeVoir/Lambert SHORT TERM...Lambert LONG TERM...Lambert/Tyburski AVIATION...Steinbugl CLIMATE...

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