Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 210856 AFDCTP Area Forecast Discussion National Weather Service State College PA 456 AM EDT Sat Oct 21 2017 .SYNOPSIS...
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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.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The weekend will kick off with clear and light wind, allowing mins around sunrise dip into the upper 30s to lower 40s in most locations. The perennial rural valley cold spots will see temps settle in the mid 30s with a touch of frost, while the hilltops see a light south to southwest breeze with mins a bit milder and in the mid to upper 40s. Expect patchy 1SM fog at worst in some of the Susquehanna`s Middle and West Branch Valleys, along with the valleys containing tributaries to the north. 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.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
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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.
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&& .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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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 well. 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.
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&& .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... High pressure over Pennsylvania will ensure VFR conditions and light wind through tonight. Some isolated pockets of valley fog are possible between early this morning, but the odds of any terminal impacts remain low. Outlook... Sun...Patchy AM valley fog possible, mainly KLNS. Mon...Patchy AM valley fog possible. Increasing clouds. Tue...LLWS. Sharp FROPA/wind shift. Gusty showers with locally heavy downpours possible. Breezy but improving Tues night. Wed...Low cigs possible west. && .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...Lambert SHORT TERM...Lambert LONG TERM...Lambert/RXR AVIATION...Fitzgerald/Steinbugl CLIMATE...

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