Area Forecast Discussion
Issued by NWS State College, PA

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100 FXUS61 KCTP 060720 AFDCTP Area Forecast Discussion National Weather Service State College PA 220 AM EST Tue Dec 6 2016 .SYNOPSIS... A storm system will move in from the Gulf Coast states and affect the region Tuesday into Tuesday night. Much colder air will move in after a cold front passes on Wednesday. The end of the week will feature a prolonged bout of lake effect snow and much-below normal temperatures. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... The overnight will be fair and dry under increasing mid and high cloudiness. Lows will drop back in the mid 20s to low 30s across the region. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/... A low pressure system with some moderate upper level forcing will be moving into the region tomorrow morning. The high pressure bubble that will be over the region today will move quickly to the northeast. A low will move into the OH valley late Tuesday with the earliest bands of precipitation from this storm reaching southwest PA by Tuesday morning. The most difficult part of the forecast is the p-type. The latest NAM brings in precipitation between 12Z to 15Z with some warm air advection aloft. However evaporative cooling should take the warm air advection quickly down to the wet bulb which should switch the precipitation type to snow. So there remains the threat of freezing rain/sleet through the Laurels with generally a wet snow/rain event through the rest of the region. There is still a slight chance for some mixed precipitation through the Lower susquehanna but given marginal temperatures and quickly cooling mid levels have left the area out of the advisory for now. Have the advisory with freezing rain for the Laurels but as the region warms during the daytime a rain/snow mix will intrude and switch to snow as the day continues. Since any snow falling will be fairly wet, accumulations are tricky. The Central mountain temperatures and through the northeast should be cold enough for a couple inches to be probable. At this time, we will keep the 12-24 hr forecast snow amounts around 1-2" with the highest amounts over the NC mtns. So tomorrow will be fairly wet with slippery roads. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... The long term period will begin with the rather quick ENE departure of the synoptic wintry precip event. Wet bulb/thermal profiles the first half of Tuesday night area just cold enough for mainly snow across much of central and northern PA with light additional accumulations of snow sleet (and patchy -FZRA across the Laurels) as the brunt of the stronger southerly Warm advection and UVVEL will be racing off to the northeast with adiabatic and evaporational cooling being overcome by the weakening warm advection bringing the sfc to 925 mb temps to around or just above Zero C in the 06-12Z period Wednesday. Expect some lingering -SHSN/-SHRA Wednesday morning along and just in the wake of the CFA (within a period of mdtly strong, 925-850 mb cold advection and westerly upslope flow across the Alleghenies). High Pressure and drying noses in from the west Wednesday afternoon and night with partial clearing across the central ridge and valley region and beneath a fast WSW flow aloft. Temps Wednesday through Thursday will be near to slightly below normal. Broad and weak to moderate large scale lift/low to mid level warm advection develops late Wednesday night across the mtns of Wrn PA, and spreads across the remainder of Central PA Thursday ahead of an approaching arctic front and beneath the thermally direct segment of a 150kt 300mb jet moving by just to our north. The subsidence inversion base lifts rapidly up to 7-10 kft agl Thursday afternoon, right through Friday night. The mean wind in the 925-850mb layer veers from about 270 deg to 295-310 deg Friday and Friday night creating the likelihood of a significant/heavy Lake Effect/orographic snow event for the NW mtns (i.e. mainly the snowbelt of NW Warren county), and in a few preferred locations across the Laurel Highlands. Gusty NW winds could top 40 mph at times Friday. The large area of High Pressure and modified arctic airmass will slide off the east coast Sat night and Sunday. The coldest temps of the season so far will occur Sat night/early Sunday with lows in the lower to mid teens across the snow covered ground of the NW/Ncent mtns...and upper teens to l20s elsewhere. a chance of some like snow/snow showers returns with a warm front Sunday night/Monday. The boundary layer could become warm enough by Monday night to mix in rain showers. especially throughout the central and southern valleys. && .AVIATION /07Z TUESDAY THROUGH SATURDAY/... MVFR cigs over the northwest airspace should trend to VFR over the next several hours. Elsewhere expect VFR with increasing/thickening high clouds. Cigs will lower from south to north later this morning with precip spreading over the airspace by the afternoon. P-types should transition from frozen/freezing to rain/drizzle across the western 2/3 of the airspace into Tuesday night. The southeast airspace should see mostly rain with some sleet possible at the onset. Confidence in ptypes is marginal given complex and evolving thermal structure/evaporative cooling in the boundary layer. Elevation and pcpn rates will also be a factor. A period of LLWS is possible at BFD/JST from roughly 6/18z-7/03z. Overall, expect flying conditions to deteriorate with high confidence in sub-VFR Tuesday afternoon into Tuesday night. Outlook... Wed...A.M. low cigs becoming mainly VFR. Thu-Fri...Becoming windy with periods of snow showers. Mainly MVFR/IFR west to MVFR/VFR east. Sat...Decreasing winds. Low cigs/-SHSN psbl NW. VFR east. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 6 AM this morning to midnight EST tonight for PAZ024-033. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Ceru LONG TERM...Lambert AVIATION...Gartner/Steinbugl is the U.S. government's official web portal to all federal, state and local government web resources and services.