Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 172124 AFDCTP Area Forecast Discussion National Weather Service State College PA 424 PM 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/... Mostly sunny conds will continue remainder of the day with high clouds on the doorstep for later this evening. Low clouds have finally dissipated across the nw. Max temps 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 6 PM SATURDAY/...
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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.
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One-two punch of gusty West to Northwest wind, then a quick transition to the first significant bout of Lake Effect Snow this season across the NW mtns of PA in the wake of a strong cold frontal passage Saturday night. 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. The center of an area of very sharp pressure rises (10 mb/3 hours) moves ENE right over the region during the mid to late morning hours Sunday. We could easily see Wind Advisory Criteria with this type of fall/rise couplet passing directly overhead, and possibly even a High Wind Watch/Warning scenario with west to northwest gusts in the 50-60 mph range. It`s still far enough out to look for consistency in this feature and decide whether to go the High Wind Watch route at ~4th period. The second punch is the deep/strong cold air advection with -10C air at 850 mb crossing Lake Erie Water temps in the mid-upper 40s, which results in an extreme Lake-850 mb Delta T of 18C Sunday afternoon and evening across the perennial snowbelt of NW PA. Winter Weather Advisory criteria will likely be reached from this upcoming bout of LES, considering anticipated 4-8 inch forecast snow amounts over an extended 24-36 hour period. Elsewhere, much lighter snow amounts of a coating to 2 inches will occur from sinuous bands of snow showers and briefly heavy squalls that should make it well into the Central Ridge and Valley Region and portions of the Susq Valley based on fairly strong 35 to 45 kt nw winds in the deep and cold boundary layer. High pressure sliding by to our south will influence the weather to start Thanksgiving week, bringing a couple of cool- dry days. Temperatures will begin to moderate Tuesday with a gusty SW flow expected to develop as potent sub-1000 mb low pressure passes by across southern Ontario and Quebec. Tuesday will be the lone day in the Mon-Fri period when 850 mb temps will poke a few to several deg C above zero. Though the 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 periods of snow showers (with light accums of a coating to 2 inches) back into the NW zones, along with a return of slightly cooler air. Flurries or brief snow showers will occur just SE of the Allegheny Front. 12Z GFS and EC have trended into better agreement on a deepening upper low across southeastern Canada or the NE U.S. over the Thanksgiving weekend. Surface and 850 mb temps could be a few deg colder than our upcoming cold outbreak later this weekend.
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&& .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/... As high pressure builds across the region, expect VFR conds through at least the late eve hours and overnight at most airfields. Stratocu cigs have finally lifted at KBFD Complex frontal system will affect the region through the weekend with rain spreading west to east starting late tonight. 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. Wed...Cold fropa. Shra/shsn psbl, mainly northwest. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo/Gartner NEAR TERM...Gartner SHORT TERM...Dangelo/Gartner LONG TERM...Lambert AVIATION...Fitzgerald/Gartner is the U.S. government's official web portal to all federal, state and local government web resources and services.