Area Forecast Discussion
Issued by NWS State College, PA

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686 FXUS61 KCTP 090329 AFDCTP Area Forecast Discussion National Weather Service State College PA 1029 PM EST Thu Dec 8 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 FRIDAY MORNING/...
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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.
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&& .SHORT TERM /8 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... 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 /FRIDAY 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 noticably below normal temps filtering in for the rest of next week. && .AVIATION /04Z FRIDAY THROUGH TUESDAY/...
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03Z TAFS sent. Starting to see stronger radar returns near BFD, as winds shift more to the NW and bands of snow showers shift southward into northern PA. Earlier discussion below. Shear axis moving across the region this evening. Westerly flow will become more northwesterly overnight. Some snow showers may get as far southeast as UNV and AOO. Main areas to see snow showers will be BFD and JST. Little change is expected before Saturday afternoon, when winds shift more to the southwest. Warming aloft and the wind shift at this point should allow the lake effect snow showers and upslope snow showers to come to an end. Outlook... Sat...MVFR/IFR with snow showers in the morning. Improving conditions in the aft. Sun...Becoming MVFR/IFR with some snow. Rain may mix in at times. Mon...Additional rain and snow. MVFR/IFR conditions. Becoming windy late. Tue...Mainly dry with VFR conditions. MVFR/IFR still possible acros the north and west with snow showers.
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&& .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...Martin

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