Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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985 FXUS61 KPHI 082010 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 310 PM EST Thu Dec 8 2016 .SYNOPSIS... An area of low pressure will continue to slowly drift across eastern Canada today through Friday, and end up south of Greenland by Saturday. With high pressure to our west, a strong west to northwest flow will remain through the end of the week. High pressure briefly affects the area Saturday night, then moves offshore Sunday. A warm front is expected to lift across the area Sunday night, before an area of low pressure is forecast to move near or just north of the area around Monday. This system will pull a cold front across the area Monday, then another quick moving frontal boundary may move across the area around Tuesday night. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Morning summary: had a smattering-scattering of .01 rainfall this morning southern 2/3rds De and a ptn of Md E shore. Remainder of this afternoon...west wind will continue increasing to 22-28 kt around 21z then should decrease after sunset but PHL may gust 18-20 kt all night. Tonight...mostly clear with a light west-northwest breeze except PHL may gust 18-20 kt all night as well as adjacent all bodies of water as boundary layer temps show increasing land-sst differential and resultant enhanced land breeze effect, near the water. Exception to the mostly clear skies: near the Poconos where lake effect clouds arrive and then flurries should eventually develop there sometime tonight. Fcst was a 50 50 blend of the 12z gfs/nam mos guidance. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Cold air advection and lake effect streamers of moisture, flurries and snow showers from the Great Lakes combined with the cold trough aloft increase the snow squall probabilities tomorrow and so at least sct flurries to near I-95 (not expecting flurries or sprinkles along the coast) and suspect small accumulation in parts of poconos Friday afternoon. A snow map will post shortly followed by snow probs around 5PM for this first little terrain related accumulation event. otherwise...mostly sunny skies to start (mo cloudy Poconos) becomes considerable cloudiness everywhere during the afternoon. Breezy with west northwest wind gusts 25 to possibly 30 mph. FCSt basis was a 50 50 blend of the 12z gfs/nam MOS and added a degree to the max T per the 12z/8 EC 2m temps. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... FB posted and tweeted WPC mid shift Day 4 winter prob 1/4" w.e. outlook. Briefing package will post on the web tomorrow. Low pressure continues to drift across eastern Canada Friday, then moves offshore and ends up south of Greenland by Saturday. Meanwhile high pressure remains across the central part of the country. This will keep a steady west to northwest flow across the area. On Friday, although the strong vorticity impulse is expected to be east of the area, there will remain steep low-mid level lapse rates across the area with enhanced moisture as well. With the strong northwest flow, it is possible that some lake effect streamers could set up and bring some snow showers/flurries to portions of the area. The best chances would be across the northern portions of the area, so we keep scattered/isolated snow showers/flurries there. Elsewhere we will keep isolated flurries/sprinkles. On Saturday, the steep lapse rates and moisture combination lifts northward some. We`ll keep isolated snow showers/flurries for the far northern counties, but will keep flurries/sprinkles for the middle half of the area as the northwest flow begins to weaken some, so the flurries may not have as great of a reach southward as on Friday. While most areas probably won`t see much snow accumulation Friday and Saturday, if any snow bands or squalls do develop, it would not be surprising to see some accumulating snow in some areas. High pressure briefly affects the area Saturday night, providing dry conditions. Friday and Saturday will be a cold and windy period, with Friday being the windiest, and Saturday being the coolest of the two. The high builds offshore Sunday ahead of the next storm system. As this happens, it is possible that some showers could develop during the day across the area as a short wave passes just to our north and spreads an area of moisture across the area. However, the best chance of precipitation looks to be Sunday night into Monday. A warm front is forecast to lift across the area late on Sunday night into Monday as an area of low pressure is forecast to move near or just north of the area. Conditions should be cold enough overnight Sunday into Monday for a period of snow to affect a good portion of the area, before much of the area warms up and precipitation turns to rain during the day Monday. There is the potential for an accumulating snow for much of the area, with the northern half having the greatest potential. As the low continues to lift northward, a cold front is expected to move across the area late in the day Monday and overnight. Precipitation chances should diminish behind the cold front. On Tuesday and Tuesday night, the GFS is indicating another cold front moving across the area as low pressure passes to our north. It in turn brings a period of rain and snow to the area late Tuesday into early Wednesday. The ECMWF does not have as strong of a cold frontal passage, so it does not bring any precipitation to the area. For now, we`ll introduce a small chance into the forecast. && .AVIATION /20Z THURSDAY THROUGH TUESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Remainder of this afternoon...VFR sct clouds aoa 4000 ft. West wind with gusts increasing 22 to 28 kt by 21z. Already 25 kt PHL. Tonight...VFR mostly clear. wnw wind with scattered gusts 15-20 kt, mainly PHL area. Friday...Generally VFR sct-bkn aoa 4000 ft, although CIGS may briefly lower to MVFR in scattered snow showers e PA nigher terrain. An afternoon flurry or sprinkle is possible to ILG-PHL- TTN. Gusty west to northwest winds 22-30 knots. OUTLOOK... Friday night - Saturday...Generally VFR, although CIGS may occasionally lower to MVFR. Scattered showers or flurries/sprinkles are possible during the daytime of each day which may temporarily lower conditions. Gusty west to northwest winds 15-25 knots, strongest winds Friday which may approach 30 knots at times. Sunday...VFR early, possibly lowering to MVFR by the afternoon. Rain or snow possible late in the day. Sunday night-Monday...Conditions continue to lower to MVFR and then IFR. Rain or snow becoming likely. Accumulating snow possible for eastern Pennsylvania, much of New Jersey, and the northern portions of the Delmarva. && .MARINE... Gale warning posting momentarily for lower De Bay and adjacent DE, Cape May waters. and a gale watch is posted for Fri-Fri eve per collab with OKX. Many reports 29kt upstream. The wind orientation down De Bay, steep lapse rates possibly manufactures several more kts of wind than modeled in the caa pattern. NAM sounding indicates mid 30s gales possible. May need a marginal mid 30s gale for the remainder NJ waters 10z Friday - 06z Saturday and issuing a watch for that area shortly. OUTLOOK... Friday night-Saturday...Small Craft Advisory in effect through Friday night, which may need to be extended into Saturday. Winds may approach gale force at times on Friday. Saturday night...Winds expected to drop below Small Craft Advisory levels, but pick up again late Sunday. Sunday-Sunday night...Winds may increase and approach Small Craft Advisory levels at late in the day into the overnight. Monday...Small Craft Advisory conditions possible. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EST Saturday for ANZ430- 450>452. Gale Warning from 6 PM this evening to 6 AM EST Friday for ANZ431-453>455. && $$ Synopsis...Robertson Near Term...Drag Short Term...Drag Long Term...Robertson Aviation...Drag/Robertson Marine...Drag/Robertson

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