Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 041716 AFDCTP Area Forecast Discussion National Weather Service State College PA 1216 PM EST Sun Dec 4 2016 .SYNOPSIS...
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High pressure will slide quickly off to the east today. A weak frontal boundary but rather potent upper air disturbance will pass through tonight. Another storm system will affect the area during mid-week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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850 mb ridge just entering the western mtns late this morning...with a general northwest flow around that level persisting across central and eastern sections of the state. This flow was trapping a layer of high based strato cu beneath an increasing mid and high level cloud deck. Ovc skies, dry conditions and light variable sfc winds will persist for the rest of the day. Temps this afternoon will peak in the upper 30s across the Alleghenies and in the low-mid 40s in the central and southern valleys. Little change in the previous thinking for the weather type, and onset timing for tonight. Precip should arrive this evening in the SW and spread steadily across the rest of the region. A 3-6 hour period of precipitation is expected - starting as snow/sleet in most places. The most challenging part of the near term period is the type of precip and how much if any accumulation of snow - or even some freezing rain - there will be. Temps seem to stay just a bit too mild for much of an accumulation of either. However, the Laurels may drop below freezing for a period in the middle of the night as the temps begin to rise aloft and turn the precip to rain. This could allow for some FZRA in the southwest - most likely confined to the highest elevations. Not enough confidence in temps being below freezing for very long where it does turn to rain in order to post a FZRA (or winter wx) advisory just yet. Have mentioned it in the grids, but kept out mentions of FZRA accretions. Temps will likely be mildest overnight in the SCtrl/SErn counties. Otherwise, there is enough QPF and will likely be enough of a cooling effect from the precip falling into the 20-something dewpoint air to make a light coating of snow/sleet across much of the area. Have kept a general 1-2" in the north and an inch or less in the central and a little less still in the south. The precip could turn to rain at the very end, but will likely just decay into some patchy drizzle. This, too, could spell trouble if it lingers into rush hour Monday morning and if temps can stay below freezing.
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&& .SHORT TERM /MONDAY THROUGH TUESDAY/... The fast flow aloft takes the best forcing for precip off to the east of the area early Monday. Will linger some sct -SHSN/RA in the east and along the west/high elevations during the morning. It should dry out through the day. But, much like today, Monday will be just a brief break from precip. Another system will try to gel to our west. This one will have a former cutoff low from old Mexico as it`s forcing mechanism. The low will cross the border early Monday and open up as it slides NE into the OH valley Mon night and overhead on Tuesday. A broad but weak low will form over the lower MS valley and perhaps do a split with one spot of lower pressure going up the OH river and another one more to the south which would eventually move over the DelMarVa peninsula. Without a very solid low moving to our south, I have a low confidence in keeping all the precip frozen. Similarly, without a distinct low going to the west of us, I also have trouble pushing the warm air over the entire area and turning things to all rain - as it looked like would be possible when I saw the model output last night. At this point, it seems like there will be a transition from a very brief period of mixed precip to a longer period of rain. However, the NEthird of the area may stay cold enough to allow for an inch or so of snow. Another small chance for freezing rain does exist - but the precip will be falling during the day, and temps should rise above freezing after the precip begins but probably before noon passes. Even the northern mountains should get into the m-u30s. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... The end of the week brings some model disagreement with the GFS/GEFS being faster than the ECMWF with the next large upper trof and frontal system. Either way, precip looks like a good bet around the Thu/fri period as all solutions eventually bring this trough through. So predictability is increasing, but timing issues remain. Best bet for precip at this point is mainly rain over the SE as decent push of warm air lifts ahead of the system, with a rain/snow mix further north where warm air will not infiltrate as much. Behind the trough, looks like a chilly weekend in store with a potential sharp dropoff in temps. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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Mean ridge in the 3-6 kft agl layer was over the Alleghenies of western PA late this morning. A Typical WNW flow regime persisted just ahead of this ridge, with MVFR ceilings across the Western and Northern Mountains, with VFR ceilings across central and eastern airfields. Little change in conditions will occur this afternoon, though some of the lower/MVFR clouds will break as the llvl ridge slides east across the forecast area. Light precipitation moves in tonight. Mainly rain in the southeast...a rain/snow mix in central areas...and mainly snow in the north and northwest. Outlook... Sun...Morning restrictions in mountains, then VFR. Sun Night...Mixed rain/snow event with restrictions. Lowest conditions in the mountains north and west. Mon...No sig wx expected. Tue...Mixed precip/low CIGs possible, especially late. Wed...Lingering low CIGs possible. Thu...Mixed precip/low CIGs possible.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo/Lambert NEAR TERM...Lambert/Dangelo SHORT TERM...Dangelo LONG TERM...Gartner/RXR AVIATION...Lambert/Gartner

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