Area Forecast Discussion
Issued by NWS State College, PA

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816 FXUS61 KCTP 232150 AFDCTP Area Forecast Discussion National Weather Service State College PA 550 PM EDT Wed Aug 23 2017 .SYNOPSIS... A large are of high pressure will build southeast across the region and bring mainly dry and cool weather with comfortably low humidity during the day. A weak upper level disturbance and pool of cold air aloft could spark some scattered showers or sprinkles across the central and northwest mountains Thursday afternoon. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Southern edge of much cooler mid level temps will slide across northern PA this afternoon bringing vertically enhanced cu and possibly a few sprinkles. Elsewhere across central and southern PA, much flatter fair weather cu will be generally in the scattered sky cover category. Temps will be pretty close to normal in the SE half of the fcst area, but about 3 to 5F below normal in the NW half, especially on the hill tops. Cold air in the form of 8H temps as low as +6C (1-2sigma below normal) will slide across the Great Lakes and settle in for quite a few days. Boundary layer decoupling will lead to calm air tonight which will help to maximize radiational cooling and help fog to form in the valleys, but some cloud cover over the west may keep the fog in check. Mins will be 45-60F across the area. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... A potent short wave trough will push across the Great Lakes late Thursday or Thursday night. The NAM is quickest with this feature, but most other models delay the window of best forcing until Thurs night. This feature is strong enough that - even without anything more than meager lake moisture - it could generate an organized area of showers. Due to the timing uncertainty and lack of deep moisture, POPs were capped at 50 percent across the northwest mountains, and generally slight chance across the central ridge and valley region of the state. High temps Thursday will be about 5-6F lower than this afternoon`s (Wed) values, or in the m60s NW-m70s SE PA. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... An extended period of refreshingly cool, pleasant and dry weather will continue through the upcoming weekend as high pressure remains in control of the weather pattern over the northeast quarter of the CONUS. It will feel more like early fall than late summer. A few spots in north-central PA could see morning lows dip into the upper 30s over the weekend. Global models suggest isolated, terrain-induced convection may be possible within return flow along the spine of the central Appalachians later in the period. However, ensemble means favor a continuation of the mainly dry and seasonable pattern through the end of August, as upper level ridging building into the Western U.S. supports troughing downstream over the central and eastern states. Interesting to note that the both the 12Z GFS/00Z ECMWF bring the remnants of Harvey toward the area by early September. After what appears to be a mainly dry end to the month of August in central PA, this could be something to monitor down the road. && .AVIATION /22Z WEDNESDAY THROUGH MONDAY/...
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A ridge of high pressure building into the region will ensure VFR conditions and a diminishing breeze this evening. Some patchy dense valley fog is likely late tonight, mainly in the valleys of northwest Pa. Based on latest SREF, downscaled NAM and LAMP guidance, believe a period of IFR/LIFR conditions is likely late tonight into early Thursday morning at KBFD, with a brief period of fog also possible at KUNV/KAOO/KIPT around dawn. Elsewhere, believe MOS guidance is overly pessimistic at KJST, where radiation fog is rare due to its ridgetop location. Based on climatology and latest model guidance, believe most of the fog across northwest Pa will burn off by around 14Z. There is high confidence in widespread VFR conditions the rest of Thursday. However, can`t rule out a brief MVFR reduction from a passing shower in the afternoon. .OUTLOOK... Friday-Sunday...Other than a few hrs of low cigs and vsbys in patchy dense valley fog between 09-12Z Friday, Sat and Sunday mornings, No sig wx is expected.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Steinbugl AVIATION...Fitzgerald/Lambert

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