Area Forecast Discussion
Issued by NWS State College, PA

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428 FXUS61 KCTP 090618 AFDCTP Area Forecast Discussion National Weather Service State College PA 118 AM EST Fri Dec 9 2016 .SYNOPSIS... A upper level trough over the Great Lakes will pivot eastward across the region over the next couple of days. A prolonged period of lake effect snowfall will bring significant snow accumulations to northwest PA through Saturday. High pressure will briefly build into Pennsylvania late Saturday, then a weak low pressure system is likely to track west of Pennsylvania through the Great Lakes Sunday into Monday. Unsettled weather will persist next week with additional storm chances by both mid week and again late next week. && .NEAR TERM /UNTIL 8 AM THIS MORNING/... The big band broke up almost completely as expected and the snows are re-orienting to more of a general area and should go to short-fetch bands in a couple of hours. The connections to upstream lakes should not form until late tonight or early Fri. Interestingly, the newest NAM actually paints a picture of an extremely long fetch band/qpf beginning in LS, then over LM, over Saginaw Bay (part of LH), over far srn LH (pretty close to Lake St Clair), and finally over LE into NW PA on Fri! Wow. If it can really manage to pull moisture from 5 of the 6 Great Lakes (yes, Lake St Clair counts) with one band, that would be impressive. Prev... The main band is hanging over wrn NY and piling it onto nrn/cent Chaut and Catt Cos. Saw BUF had a report of 17" of new snow in Perrysburg - only HiRes WRF- ARW seems to be doing really well at placement of the band and surrounding lighter area of SHSN coming off LE. It along with the HRRR make a decent 20-30 degree veering to the mean llvl wind and quickly break the main band up before midnight - if not by 10 PM. The shorter fetch keeps the smaller and more numerous bands within 70mi of the lake shore for a bit until a good LH/Georgian Bay connection(s) develop later tonight. Have tried to draw this into the POPs for the next few hours. Otherwise all is as expected. Prev... Mid cloud deck associated with sheared 5h trough exiting my southeastern counties this afternoon. Meanwhile...colder air overspreading western and central areas has promoted stratus development and flurries reaching into the central mountains. Organized intense lake effect snow banding remains north of the PA/Ny border as expected...and HRRR continues to indicate a slow southward drift in time tonight...with moderate snowfall and accumulations dropping south of the PA/NY border tonight.. Radar imagery shows clear trend shore-hugging snow banding along the Lake Erie shoreline for now...thanks to lee shore troffing induced by warmer lakes. Consensus of hi res models drops the main band southward towards PA tonight before event evolves into a Lake Huron connection with NW to SE oriented bands overnight into Friday morning. Little change to forecast storm total snow amounts as 12"+ locally expected over western portions of Warren County by Saturday. Mins tonight will range from the lower 20s northwest to the upper 20s southeast. && .SHORT TERM /8 AM THIS MORNING THROUGH 6 PM SATURDAY/... Long duration lake effect snow event continues on Friday as anomalously cold cross-lake flow maintains multiband le snow event across the northwest Pa. Model soundings showing a deep, moist boundary layer with an inversion height around 700MB and although the 850mb temps of around -11 to -14C sufficient to maintain moderate to heavy banding from relatively warm lake waters of around 50F. The passage of a shortwave around midday Friday could briefly support lake effect snow extending well downwind of the lakes, with a quick coating likely in the ridge/valley region of Central Pa and possibly even into parts of the Susq Valley. The boundary layer flow is progged to remain close to 270 degrees across Southern Pa, excluding the Laurel Highlands from a direst link to lake moisture. However, persistent upslope flow should yield occasional light snow with accumulations of 1-2 inches between Friday and Sat morning. Although not an exceptionally cold air mass for this time of the year, this will be the coldest air mass so far this season with temps 5-10F below normal Friday/Saturday. A gusty wind will make it feel even colder. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Gradually improving conditions heading into Sat across the NW Mtns as lake effect snow bands become more scattered and slowly wind down. Still potential for a renegade snow band (with Lake Huron connection) to stretch into the central mtns Fri night with localized impacts though as trough lifts out. However, WSW fetch off the lakes should continue to produce snow showers until Sat evening across the N Mtns. Breezy winds abate Fri night, with clearing skies across Southern Pa late Friday night and Saturday as surface high pressure builds in from the Ohio Valley. High pressure will bring a brief period of tranquility Sat evening. However, a developing overrunning scenario is expected Sunday into Monday, as weak low pressure lifts into the Eastern Grt Lks and high pressure remains lodged over northern New Eng. Enough cold air is in place to support a light snowfall across much of area by Monday AM, with GFS bringing light precip into the area on Sunday earlier than the ECMWF. Model consensus low track west of PA should bring in enough warm air to cause snow to change to rain across Southern PA, and esp the Lower Susq Valley, a before precip tapers off later Monday. A bit cooler than normal temps indicated early next week, but longer range models indicate a significant cold front passage Wed with noticeably below normal temps filtering in for the rest of next week. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... Cold W-NW flow pattern downwind of the Great Lakes will continue to support a prolonged period of MVFR/IFR conditions over the western 1/3 of the airspace into the weekend, with frequent lake effect/upslope snow showers at KBFD/JST. MVFR cigs and ocnl visby reductions in -shsn are possible over the central terminals with VFR prevailing across the eastern sites. Expect sfc wind gusts 20-25+kt from 270-300 degrees for most of today before winds subside after 10/00z. Lake effect snow showers should decrease in coverage and intensity by later Saturday as area of high pressure briefly slides over the airspace. Low pressure tracking from the lee of the Rockies to the Ohio Valley will bring a broad area of snow/rain to the area Sunday into early Monday. Outlook... Sat...MVFR/IFR western 1/3 with snow showers decreasing. Sun-Mon...Widespread MVFR/IFR in snow/rain. Becoming breezy Monday night with snow showers over the wrn 1/3. Tue...VFR to MVFR cigs. Snow showers ending. && .CTP WATCHES/WARNINGS/ADVISORIES... Lake Effect Snow Advisory until noon EST Saturday for PAZ005. Lake Effect Snow Warning until noon EST Saturday for PAZ004. && $$ SYNOPSIS...DeVoir NEAR TERM...Dangelo/DeVoir SHORT TERM...DeVoir LONG TERM...Fitzgerald/RXR AVIATION...Steinbugl is the U.S. government's official web portal to all federal, state and local government web resources and services.