Area Forecast Discussion
Issued by NWS State College, PA

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851 FXUS61 KCTP 260917 AFDCTP Area Forecast Discussion National Weather Service State College PA 517 AM EDT Wed Oct 26 2016 .SYNOPSIS... A dry and chilly day will be followed by a dose of cold rain later tonight into Thursday with a wet snow accumulation possible from the Northern Alleghenies into Poconos. Chilly air will hold its ground through the end of the week with some moderation in temperatures expected over the weekend and into next week. && .NEAR TERM /THROUGH TONIGHT/... With the exception of the Harrisburg metro area, 08z observations show freezing temperatures (26-32F) across the majority of Central Pennsylvania. Expect temps to drop a few more degrees prior to daybreak which should ensure an end to the growing season for the counties in the Freeze Warning. A sunny start should begin to fade behind increasing clouds from west to east this evening as a low pressure system tracks from IA over Lake Erie tonight into early Thursday morning. Strong warm air advection and isentropic lift via strong SSW low level flow will support expanding zone of pcpn overrunning a retreating cold airmass ahead of the aforementioned area of low pressure. This should bring a cold rain along with some wintry weather concerns across the Northern Alleghenies into the Endless Mtns/Poconos. Evaporative cooling/web bulb effects should allow for a period of wet snow/sleet at the onset before a transition back to rain occurs later Thursday morning as the boundary layer slowly warms up. If temperatures can drop at or below freezing, would not rule out some pockets of freezing rain as temperatures warm aloft, but high resolution ensemble blend keeps surface temps AOA 32F. Marginal low level temperatures near freezing and relatively warm surfaces given time of year/first snow make for a difficult winter wx fcst with snowfall somewhat dependent on elevation, rate and type of surface (grass vs. pavement) with northern valleys likely having little to no accumulation. The time of day (overnight-predawn) is most favorable for early season accums and also most problematic in terms of impact to the AM commute. Secondary roads over the highest terrain could be slushy for a time with some slick spots. Therefore, will highlight potential winter wx threats/risk in the HWO for now and allow dayshift to assess possibility of an advy given the early season aspect and timing impact. The 26/00z NCAR ensemble and SPC SSEO both add confidence to winter ptypes with the NCAR more in line with conceptual snow-mix-rain dominant ptype progression while SSEO seems to favor more fzra/ice. The dayshift should have the HRRR available for additional consult. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Lingering wintry ptypes should transition to plain rain by later Thursday morning in the northern tier. Elsewhere, a chilly rain will expand south/east and continue through the afternoon before tapering to showers from west to east into Thursday night. Downstream blocking should allow northern stream energy to phase with the lead trough and eventually result in a negatively tilted trough over the Northeast U.S. by Friday morning. Models show the formation of a triple point low deepening along the coast into the Canadian Maritimes by Saturday morning. A brisk northwest flow may afford some lake enhancement to shower activity Thursday night and temps are cold enough to mention rain/snow showers especially in the orographically favored areas downwind of Lake Erie. Overall the trend should be toward drier conditions into Friday. The wind gusts may end up being a little stronger than forecast on the backside of the intensifying low. High pressure briefly returns later Friday afternoon/evening before shifting southeast Friday night into Saturday morning as low pressure tracks across the Upper Great Lakes. && .LONG TERM /SATURDAY THROUGH TUESDAY/... Models and ensembles generally agree in bringing a weakening cold front through the area on Saturday and stalling it out near the PA/MD border. POPs are in the chance range mainly over the NW 1/2 with little in the way of moisture/QPF. The EC/GFS seem to be trending toward the idea of a wave of low pressure developing to the west along the wavy boundary and possibly bringing a better chance for appreciable rainfall /0.25-0.50 inch/ to southern PA on Sunday. Beyond Sunday, high pressure dominates the pattern favoring dry weather. A noticeable rebound in temperatures appears likely on Saturday with an ensemble blend yielding highs 10-15 degrees warmer than Friday. Temperatures may fall back on Sunday before moderating again into early next week as southerly flow develops ahead of low pressure in the Upper Midwest. && .AVIATION /07Z WEDNESDAY THROUGH SUNDAY/... As the region has decoupled and temperatures have dropped, generally VFR skies will dominate the pattern. However due to the low temperatures and low dewpoint depressions there remains a chance for patchy valley fog overnight through the early morning hours. The mains area of concern is mainly along/in the river valleys. The only TAF sites that are of concern is BFD and JST, though JST still has weak northwesterly flow which should alleviate any fog/mist from forming. Wednesday will be VFR ahead of a storm system that will be moving into the lower great lakes late in the day. A warm front will lift north into the area Wednesday night and Thursday bringing widespread reduced conditions. Outlook... Fri...AM shrasn/low cigs possible W Mtns. Sat...SHRA w/IFR CIGs possible N PM. Otherwise no sig wx. Sun...SHRA w/MVFR cigs N and W. Breezy NW wind. && .CTP WATCHES/WARNINGS/ADVISORIES... Freeze Warning until 9 AM EDT this morning for PAZ026>028-035- 036-045-046-049>053-056>059-063>066. && $$ SYNOPSIS...Steinbugl NEAR TERM...Steinbugl SHORT TERM...Steinbugl LONG TERM...Steinbugl AVIATION...La Corte/Ceru is the U.S. government's official web portal to all federal, state and local government web resources and services.