Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 171132 AFDCTP Area Forecast Discussion National Weather Service State College PA 632 AM EST Fri Nov 17 2017 .SYNOPSIS... High pressure will build across the state today. A potent weather system will impact the region Saturday into Monday morning. A cold front will push through Saturday night. Gusty winds and some lake effect snow will then last through Sunday night. High pressure will then improve the weather for the first half of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Breaks in the clouds now over Happy Valley and the clearing is spreading to the NW. All is on track. Still chilly today, though. Temps will be 2-8F below normal. Prev... Almost all the flurries are gone from radar. The low cloud deck looks to be breaking apart in the downslope regions. While the clouds may hang on through the afternoon in the north, most of the rest of the area will get mostly sunny. However, the maxes will only be u30s to near 50F thanks to the ridge axis staying to the west until late in the day. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... High clouds will already be thickening up as the storm off to our west musters. The high pressure continues steadily off to the east and contributes southerly/moist flow into the system, allowing for deepening. The low which is barely noticeable in the sfc pressure over the high plains will deepen to about 994mb as it cross the MS river. Warm air never really has a chance to make a difference for our temps, and just slides overhead. Rain showers will begin around sunrise in the NW and spread quickly across most of the region on Saturday. The heaviest rainfall will be over the northern counties, where many places could get between 1 and 1.5 inches. The far SE is progged to get the least rain, but there could be some instability which could enhance the showers. SPC general thunder area covers most of the CWA on Day2. The air gets cold enough quick enough that there could be some light snow at the tail end of the rain Saturday night in the western/northern mtns, but not much more than a dusting. The big story is a one-two punch as the cold front crosses. The wind will pick up and get pretty gusty. The synoptic set-up of a deepening low moving down the St Lawrence River valley and a potent short wave trough aloft swinging around the base of the longer trough is quite favorable for strong winds. We may eventually need a wind advisory for portions of the area - more so in the south. But, it is too far out at >=4th period to go sounding the gong. The second punch is the good cold air behind the front - dropping the 8H temps on the order of 15 to 20C in less than 24 hrs. The cold air will generate lake effect snow as it crosses the lakes. The fetch off of LE looks fairly short with low chances for a Huron or Georgian Bay connection. There will likely be high dir shear at first, then a quick backing to the WNW as the flow aligns vertically. So, the heavier snow should be confined within 70-80 miles of the lake shore. Some light snow is possible over the Alleghenies and down in the Laurels, but most places there won`t get more than an inch. If a So, again, the second punch is most likely an advisory-level event. Again, at 4th pd or longer, a mention in the HWO is all that is necessary at this point. The snow will taper off on Monday morning. && .LONG TERM /MONDAY THROUGH THURSDAY/... High pressure moving to our south will influence the weather to start Thanksgiving week, bringing a couple of cool-dry days. Temperatures will begin to modify Tuesday with a SW flow expected to develop. Though jet stream will remain north of the region, a quick moving trough will brush the region on Wed followed by a weak shortwave Wed night, which will bring chance for light snow showers back into the NW along with a return of slightly cooler air. GFS hangs on to this trough into Thanksgiving weekend, while the ECMWF brings a flatter 500mb flow pattern. So forecast confidence remains on the low side in the 7-10 day range. && .AVIATION /12Z FRIDAY THROUGH TUESDAY/... Satellite imagery at 09Z still showing extensive stratocu downwind of the Grt Lks, covering much of central Pa. The main concern early this morning will be at KJST, where upstream observations and model data suggest cigs will be teetering between IFR and low MVFR until 10Z-11Z. As high pressure builds in, expect stratocu to break up later this morning. KJST and KBFD will likely be the last to clear, with MVFR cigs possible until around 15Z based on latest model soundings. Northwest winds still gusting 20-25KT at 06Z, but expect them to subside later this morning with arrival of high pressure. High pressure over the region will ensure VFR conditions the rest of today and this evening with winds becoming light. Outlook... Sat...Rain with low cigs possible, mainly KBFD. LLWS possible. Sun...Windy with gusts 30-40kts. MVFR in snow showers NW. Mon...MVFR cigs/sct -shsn psbl early NW 1/4. Tue...No sig wx expected. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...La Corte/RXR AVIATION...Fitzgerald

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