Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 141154 AFDCTP Area Forecast Discussion National Weather Service State College PA 654 AM EST Thu Dec 14 2017 .SYNOPSIS... An Alberta Clipper will track across Southeastern Pennsylvania this morning, causing the widespread light to moderate snow to taper quickly to scattered light snow showers before ending shortly after the morning commute hours to work and school. Gusty west to northwest winds between 30 and 35 mph will occur for up to several hours during the mid to late morning across the South- central Mountains and Laurel Highlands. Behind this area of low pressure, a ridge of high pressure will slide across the region late today and tonight with cold, but mainly dry conditions. Another clipper will move north of the region overnight Friday and Saturday morning with limited moisture and perhaps a few periods of light snow across the Northwest Mountains and Laurel Highlands. High pressure will build across the area early Sunday with a brief moderating trend. A series of cold fronts will move across the area late Sunday into Wednesday. Windy and colder temperatures will follow for Tuesday into Wednesday. && .NEAR TERM /UNTIL NOON TODAY/... An Alberta Clipper (998 MB), was located near KPHL at 11Z and will scoot quickly to the east of the CWA by shortly after the primary morning commute hours. The combination of energy at the sfc and aloft quickly transferring to the NJ coast and downsloping NWrly LLVL flow was causing the snow area to break up and lighten up across the CWA. Elongated mid to upper vort max located just to the south and west of this sfc low will still support a few enhanced bands of snow (with vsbys briefly dipping to the 3/4 - 1 1/2SM range and accum rates of 1/2-3/4 inch/hour) mainly across the Laurel Highlands for the next hour or two. Will maintain the Winter Weather Advisory in effect for much of the CWA until its expiration at 13Z. The snow will taper off, then end between 12-13Z in most locations. Light snow could linger across the Laurels and Wrn Poconos, and the North Branch of the Susq until around 14Z, keeping roads slick as temps will only be in the upper teens to lower 20s across the central counties, but in the upper 20s to lower 30s across the Laurels and southern valleys (just south of a warm front and the sfc low track). Descending, thermally direct, left-rear branch of of a 125 kt upper jet max (over WVA) will lead to gusty west to northwest winds for several hours during the mid to late morning across the Laurel Highlands and parts of the Scent Mtns of PA with winds increasing and veering to west then NW at sustained speeds of 15 to 20 mph with gusts around 35 mph. Across the central and northern part of PA, winds will be in the 5-10 mph range from the north, before backing to the NW later this morning with gusts up to around 25 mph. Latest HRRR, HREFV2/NAM, and NCAR 3KM ENS forecast continue to imply storm total snowfall ranging from less than an inch from Chambersburg and York southward, to 3-5 inches near and just to the south of I-80 across the central Mtns, and up to 6 inches across some of the higher terrain of Cambria, Blair and southern Clearfield counties where the best mesoscale mid-level FGEN banding occurred over the past several hours. && .SHORT TERM /NOON TODAY THROUGH 6 PM FRIDAY/... High pressure will build in during the day leaving little more than some scattered snow showers over NWRN sections and possibly the Laurel highlands. Places to the SE of the Alleghenies should see a several hour period of partly to mostly sunny skies for the afternoon with just some flat and non-precipitating strato cu. Highs this afternoon ranging from the upper teens across the northern tier to around freezing in the far SE will average about 10-15 deg colder than normal for the date. A few snow showers for this evening across the NW mtns, otherwise High Pressure building in will account for light winds and cold temps. It appears that a mid level short wave diving SE across the upper Glakes this morning, and warm advection to the south of it across the Upper Miss Valley will provide a good deal of thick mid and high clouds spreading over the state tonight through Friday morning. Min temps will vary from the upper single digits over the NW mtns, to the mid and upper teens throughout the Susq Valley and Southern Tier. Increasing swrly llvl flow and weak warm advection at the sfc and within the 850-700 mb layer will lead to some periods of light snow or snow showers, that will be focused across the northern and western mtns Friday afternoon. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... A mid level wind max will drop southeast Friday night and early Saturday. Some snow showers expected, mainly across the west. I did up POPS some. Still looking mainly dry later Saturday into the first part of Sunday. A complex pattern will prevail after Sunday, with some energy from the southern branch of the westerlies becoming more active. Moisture from the Gulf of Mexico will be limited, with a ridge in place. Expect colder and more in the way of wind by later Tuesday into Wednesday. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... * Cloud/Ceiling info will be missing at KBFD until new part can be installed * Light to moderate snow occurring at all TAF sites attm, causing widespread IFR and MVFR cigs and vsbys. These conds will continue for the next several hours into the early overnight. Surface low responsible for the snow is forecast to move to eastern PA by around 12Z/sunrise Thursday. The snow will taper off quickly in the pre-dawn hours with rapid improvement setting in as the storm moves east of the area. The higher elevation terminals could remain MVFR for a good part of Thursday, but elsewhere airports should become VFR by mid morning and continue throughout the day. Outlook... Thu-Sat...Scattered snow showers and local restrictions NW/Laurels. Sun-Mon...Mainly VFR. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 8 AM EST this morning for PAZ004>006-010>012-017>019-024>028-033-034-037-041-042-045-046- 049>053-056>059. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Lambert/Martin AVIATION...Ceru/Gartner

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