Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 070435 AFDCTP Area Forecast Discussion National Weather Service State College PA 1135 PM EST Tue Dec 6 2016 .SYNOPSIS... Low pressure over PA will fill and a coastal low will deepen and move away on Wednesday. High pressure will briefly visit PA before a dry but sharp cold front sweeps southeast across the area on Thursday. A low pressure system is likely to track west of Pennsylvania through the Great Lakes Sunday and Monday. && .NEAR TERM /UNTIL 9 AM WEDNESDAY MORNING/... 1059 Update... Whatever is left is going to be barely more than drizzle for the rest of the night. Have jacked up mentions of fog as well with very high ambient moisture and little wind (at this hour) over most of the CWA. The wind over the W will continue to veer and become westerly as the dry line/cold front moves across later tonight and Wed AM. Will allow the advy to die at 11 PM. Prev... Most places are above freezing now. Have begun the process of cancelling flags by dropping the warning and part of the advy since the precip is moving on through rapidly, now. Little more than drizzle or very light snow will be left as the high clouds move away and we lose the seeder-feeder process. There may still be a pocket or two of FZDZ, but not widespread at all. Fog may become dense - especially in areas with little wind and upslope regions. Temps will likely stay within a few degs of 35F all night. Early Wed morning, the temp profile will become more favorable for flurries in the west before ending. && .SHORT TERM /9 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... Surface high pressure building into the region should supply a dry Wednesday to Central PA. However, low level moisture trapped beneath inversion and weak mixing will likely result in stubborn low clouds across the NW Mtns. A downsloping westerly breeze and some slightly drier air should result in partly to mostly sunny skies east of the Mtns. Temperatures there should respond by rising into the low-mid 40s, while cloud cover holds readings to the mid 30s across the NW Mtns. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... The long term will begin with a brief period of tranquil conditions and deep southwesterly flow, ahead of an arctic front that will be pushing across the state Thursday morning and early Thursday afternoon. Clouds will thicken up Wednesday night and early Thursday with snow showers moving into the far northwest around or shortly after midnight, then spreading SE and possibly mixing with rain showers across the Southeast half of the state Thursday morning. The subsidence inversion base lifts rapidly up to, then well over 7-10 kft agl Thursday afternoon, right through Friday night as the mean low to mid level flow becomes well-aligned from the West-Northwest. The subsidence inversion base will drop gradually down to below 7 kft agl during the day Saturday as the mean 925-700 mb flow backs to more of a west, then swrly direction by around 12Z Sunday. This scenario is very favorable for heavy, to locally excessive Lake effect snow and significant amounts of blowing and drifting snow with occasional wind gusts around 30 mph, and up to several hundred j/kg of cape being transported SE of interstate 90 leading to the potential of some Thundersnow with periods of 2+/hr snowfall rates possible, especially Thursday night through Friday night as quite anomalously cold air of -2 to -3 sigma in the 700-500 mb layer moves overhead. Posted a Winter Storm Watch for Warren and McKean counties from Noon Thursday through 7 am Saturday, and the significant bands of LES could even continue through much of the day Saturday. Snow totals throughout the perennial snowbelt of NW Warren county could top 18 inches by Saturday, with areas of 6-12 inches further inland across the SE half of Warren county and at least the NW half of McKean County. Scattered narrow bands of snow showers will stream SE into the Central Ridge and valley Region occasionally, with a coating to an inch possible in a some locations. Expect rather significant snow totals (in excess of 4 inches) to also occur across the Laurel Highlands, albeit over a more extended period Thursday night into Saturday, and with lighter snowfall rates. A bubble of high pressure at the sfc (and a weak ridge aloft) will bring a brief period of tranquility (though very cold overnight min temps) as it slides east across the forecast area late Saturday into early Sunday. Expect partial clearing (and perhaps mostly clear skies across the SE part of the CWA) for the middle third of the weekend. Deep, mean-layer flow backs to the southwest with a slug of low-mid level warm advection sliding up and over the deep/retreating cold airmass. This will create an area of steady light snow or snow showers across mainly the northwest half of PA Sunday afternoon and Sunday night. The boundary layer could become warm enough by Monday to mix in or changing the scattered light precipitation to rain showers, throughout the Lower Susquehanna Valley. One or more, weak and fast moving short waves in the zonal flow aloft could bring some light mixed precipitation in the Ridge and Valley Region, and scattered snow showers across the Alleghenies. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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Most of the precipitation is over as of 11 PM. 03Z TAFS sent. Earlier discussion below. A mixture of snow, sleet, rain, and freezing rain will continue to taper off from west to east this evening, as the coastal storm becomes the main storm. Expect a wide range of conditions into Wednesday morning. Expect most areas to become VFR by late morning on Wednesday, as the storm moves away from the area. Some snow showers will likely work into the north and west late Thursday into early Saturday afternoon, as winds shift more to the west and northwest off the Great Lakes. A weak storm system tracking northeast across the Great Lakes on Sunday may bring a few snow showers to the area late. Outlook... Thu-Fri...Becoming windy with periods of snow showers, mainly late Thursday into Friday. Mainly MVFR/IFR west to MVFR/VFR east. Sat...Decreasing winds. Low cigs/-SHSN psbl NW. VFR east. Sun...Some snow possible. Mainly late across the NW.
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&& .EQUIPMENT... Temp/dewpoint sensor at KIPT appears to be malfunctioning. Far too warm compared to meso obs and surrounding METARs. Have used a more-representative 40F for the max for today at KIPT. Techs have been advised and repair is estimated to be done on Wed. && .CTP WATCHES/WARNINGS/ADVISORIES...
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Lake Effect Snow Watch from Thursday afternoon through Saturday morning for PAZ004-005.
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&& $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Ceru LONG TERM...Lambert AVIATION...Martin EQUIPMENT...Evanego is the U.S. government's official web portal to all federal, state and local government web resources and services.