Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 242200 AFDCTP Area Forecast Discussion National Weather Service State College PA 600 PM EDT Sat Sep 24 2016 .SYNOPSIS... A large area of high pressure near James Bay Canada will drift south and becoming centered over the northeastern states on Sunday. Expect fair weather with seasonably cool temperatures through the rest of this weekend. A cold front will push through the region late Monday and Monday night and should help generate much needed rainfall on the order of a few to several tenths of an inch. Dry weather will return for the rest of next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Sharp clearing line has pressed south from Interstate 80 to the route 22/322 corridor early this afternoon and will reach the southern tier counties of PA between 19Z-21Z. The last location likely to see the clearing should be the Laurel Highlands where a bkn strato cu deck could hold tough through early this evening. Mdt near sfc cold advection will battle the still relatively high late Sep sun angle and associated warming...while notably stronger cold advection at 850 mb and a Lake Ontario/850 mb delta T approaching 20c helps to create plenty of strato cu streamers off Lake Ontario. However...the amount of subsidence and deep dry air across the nrn mtns of PA should keep skies there clear to partly cloudy. 18Z Temps in the lower 60s across the nrn and western mtns...and u60s to lower 70s in the southern valleys are nearing their max values for the afternoon...which will be near to slightly above normal for the date. Will need to back off on fcst highs across the Laurels considering the persistent bkn-ovc cloud cover there. Skies will become clear in most places by early this evening and PWATs will be below normal under the subsidence of the approaching, sprawling 1028mb area of high pressure bubble. A true taste of autumn will be in the air tonight as temps drop off into the m-u30s in the northern mountains, and 40s elsewhere. Expect at least patchy frost throughout the rural valleys of the north. With the prolonged period of very much above normal temperatures, this will be quite a shock to some. Light north winds tonight should go light and variable in the deeper valleys between 06Z-13Z Sunday. This light wind combined with clear skies and a greater than 20F air/water temp diff will likely lead to development of fog (that could become locally dense). The extent and vsby associated with the fog are still somewhat in question. The cold air draining into the river valleys will then set up a battle between the river valley fog and frost. These two phenomena are rarely coincident. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday should be stellar with low dewpoints, spectacular visibility, and just a few clouds after the valley fog lifts. After the chilly start, temperatures will rebound to around normal. Some high clouds will slide down from the NW Sunday night. These could have just a minor effect on temps. Guidance says that it should be quite a bit milder in the west Sunday night vs. Sat night. Will stay close to these numbers. && .LONG TERM /MONDAY THROUGH SATURDAY/... Clouds increase Monday ahead of significant cold front headed our way. Recent guidance continues to speed up the timing of the front. Have adjusted things accordingly and split up the wx grids. This then puts the timing of showers during the afternoon/evening in the west. Showers should be out ahead, however given the instability, diurnal heating have put in thunder possible with this timing. Certainty of rainfall for most of the area has climbed into the 60-70pct range. This will be much needed rainfall, with highest amounts Monday Night. Based on latest data have increased QPF amounts, especially where thunder is possible. The front should be through by Tuesday morning. Will linger only chc POPs in the far SE and keep them in the far NW for lake- effect and/or cool air aloft instability showers for mid- week. Temps should stay very normal for the balance of the week, though cooler. There will be another extended period of dryness. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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Clear skies and light wind across central Pa this evening, as high pressure builds into the state. Don`t expect extensive fog development tonight, given the dryness of air mass. However, cool temps and relatively warm river/stream water should result in some fog late tonight in the deep valleys of north central Pa. Current thinking is that no airfields will be affected, but can`t rule out a brief vis reduction at KBFD or KIPT with even less confidence at KUNV. Sunday...Expect widespread VFR after 14Z, which will continue through Sunday night. Outlook... Mon...PM showers/Tstms with reductions possible. Tue-Wed...No sig wx expected.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Dangelo/Ceru AVIATION...Fitzgerald/Lambert is the U.S. government's official web portal to all federal, state and local government web resources and services.