Area Forecast Discussion
Issued by NWS State College, PA

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172 FXUS61 KCTP 101919 AFDCTP Area Forecast Discussion National Weather Service State College PA 219 PM EST Sat Dec 10 2016 .SYNOPSIS... High pressure will build south of the region overnight. Meanwhile a new frontal system will approach for Sunday and Monday. It will turn sharply colder behind a cold front on Tuesday, with a shot of arctic air and frigid temperatures expected through the end of the week. && .NEAR TERM /THROUGH TONIGHT/... The long-duration lake effect event will continue to gradually wind down as the steering winds back around more to the SW and allow the snow bands to migrate north into NY. Any additional accumulations are expected to remain light. Outside of the lake effect area, expect little more than a stray snow shower of flurry spilling southeast over the Alleghenies into the Central Ridge and Valley region. Skies may actually scatter out for a few hours later today over and this evening over most of the forecast area, just in time for the next system to approach for Sunday. Lows will drop back into the mid teens to lower 20s. Latest timing shows warm advection snows beginning over my wester zones before dawn tonight. && .SHORT TERM /SUNDAY/... A Winter Weather Advisory has been issued... Snow will overspread most of the region tomorrow morning. Precip type Sunday will favor snow as the temps aloft will stay cold enough during the day. Enough warm air may sneak into SWRN zones to bring a wintry mix by late in the day, but the best chance of a mix looks to hold off until Sunday night over SRN zones. The biggest question for southern Pa tomorrow will be if they get dry- slotted after the initial shot of warm advection scoots through. This complicated the advisory decision a bit with the main reasoning for headlines over southern areas being the expected ice, which should hold off until late day or overnight. But the quick burst of snow during the day will likely start things off with deteriorating travel conditions so we decided to keep the headlines simple. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... Scattered snow showers Monday night across the Western Mtns of PA will diminish as a weak ridge of high pressure at the sfc slides east from the Ohio Valley. Tuesday will begin a cool down in temps over a several day period as progressively cold chunks of arctic air move southeast ahead of the main, sub-500 dam Polar Vortex that will be moving to near James Bay Canada by late Wednesday night. The coldest airmass of this young winter will spread into the region for Thursday and Friday. Temps Thursday could conceivably struggle to get above 10F for highs across the NW mtns. The GEFS shows a small area of -2 to -3 sigma temps at 850 mb with values around -18 F. West-Northwest wind gusting between 25 and 30 mph both Wednesday and Thursday will create wind chills of 5-10 below zero during the morning hours Thursday (mainly across the NW mtns), and only in the single digits during the daylight hours. Skies will become mainly clear with the wind dying off Thursday night as a 1025 mb sfc high build east from the nation`s heartland. This will set the stage for frigid temperatures - but several degrees above record lows. Min temps early Friday could dip to zero to 5 below across the fresh snow covered ground of the Laurel Highlands and NW mtns, and will be in the single digits to teens. Fair and dry (but very cold) weather is expected to persist Friday night. However...a moisture-laden storm will likely impact a large chunk of the region (beginning Friday) with snow changing to mixed precip of from the SW. Saturday and Sunday, clouds will thicken up quickly and precipitation will begin shortly afterward Saturday morning. It`s too early to give specifics on that storm w/resp that storm. 10/00Z EC and GEFS do infer a widespread wintry (snow) precip event...likely changing to some light sleet or fzra as the thicker seeder/feeder cloud shield slides off to the east. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... Cold WNW flow pattern will continue to back slowly to the SW eventually forcing the lake snow bands to migrate back north into NY state. The snow showers and MVFR/IFR conditions over the western 1/3 of the airspace should improve to VFR for a brief time this evening, before conditions deteriorate once again late tonight and Sunday as a new frontal system brings widespread snow. Far SERN terminals will likely remain south of the precipitation and remain VFR before conditions lower Sunday night. The snow will mix with or change to sleet and freezing rain Sunday night over the terminals south of about Interstate 80, before tapering off as some light rain or snow showers Monday morning. Outlook... Mon...Slowly improving conditions with precipitation tapering off to rain or snow showers by Monday afternoon. Tue-Wed...MVFR ceilings and light snow showers possible NW. VFR elsewhere. Thu...Restrictions possible, mainly west and north with more lake effect snow showers. Gusty NW wind. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 4 AM Sunday to 1 PM EST Monday for PAZ004>006-010>012-017>019-024>028-033>037-041-042-045-046- 049>053-056>059-063. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...La Corte LONG TERM...Lambert AVIATION...La Corte

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