Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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749 FXUS61 KPHI 092103 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 403 PM EST Sat Dec 9 2017 .SYNOPSIS...
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Low pressure off the mid-Atlantic coast will deepen as it moves northeast tonight and into the Canadian Maritime region on Sunday. Weak high pressure over the area on Monday will be followed by low pressure on Tuesday, with an associated arctic cold front ushering the coldest air of the season by Wednesday. Another fast-moving low pressure may affect the area Thursday night into Friday.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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Mesoscale Update #4 3:00 PM: Several areas of enhanced FGEN forcing are leading to several snow bands of moderate snow across the region embedded in an area of light snow, locally enhancing totals. An example is the 3 inch report we just got in from Allentown. Moisture across New Jersey is cutoff based on convection offshore and the snow bands to the west. These snow bands will rotate eastward late this afternoon and evening allowing snow to redevelop. Overall, amounts for the most part look on track with a few inches in most spots expected. Portions of southern new Jersey into central Delaware and the eastern shore of Maryland have seen the lowest totals so far with an inch or less at several DEOS sites. The HRRR and the RAP still about bring about .2- .3 QPF for many of these locations into the evening but that falls short of warning criteria. Therefore, the warning has been downgraded to an advisory outside of Sussex and Cape May county counties. Tonight: Developing low pressure off the New Jersey coastline will continue moving northeast tonight. This will bring an end to the snow and mixed precipitation along the coast this evening. Some clearing will occur by the overnight hours. Even with the clearing, an increasing westerly wind up to 10 mph is expected. This may prevent temperatures from completely tanking despite snow cover. With several factors in play it`s not a high confidence forecast on the lows but it looks like most locations will be in the upper 10`s and 20`s.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH 6 PM SUNDAY/...
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A general trough of low pressure will still be over the region on Sunday leading to a mix of sun and clouds across our area. Some moisture off of the Great Lakes has an opportunity to interact with the higher terrain of the southern Poconos and NW NJ, leading to a few snow showers and minor accumulations. However, the wind direction looks too westerly for a more widespread event. Winds will actually be the main story with bufkit analysis continuing to show the potential for 20-25 mph gusts in the afternoon. Temperatures will warm into the 30`s, likely a few degrees below a MET/MAV blend based on the snow cover.
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&& .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/...
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The pattern for the extended forecast period features a longwave trof over the eastern US with several fast-moving shortwave trofs rotating through it. Partly due to their rapid movement these systems will not be able to pick up much moisture, but temperatures will be generally cold enough for any precip to fall as snow or at least a mix. An arctic surge around mid- week will bring the coldest airmass of the season so far into our area. Some moderation is possible by next weekend. Weak high pressure over the area on Monday should provide fair wx with near normal temps. Then Monday night into Tuesday low pressure is forecast to develop over the lower Grtlks and intensify as it moves east into New England. The associated strong cold front is forecast to cross the mid-Atlantic region Tuesday morning. Some WAA is forecast ahead of this front along with possible rain or snow showers, although mainly snow snow is expected N/W of PHL. Behind the front strong CAA and gusty NW winds will persist through Tuesday night and Wednesday. A weak ridge of high pressure with fair wx is forecast for THursday but temps should remain well below normal. Another fast moving system may bring snow showers to the area Thursday night, but forecast PoPs are only in the 20-30 percent range.
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&& .AVIATION /21Z SATURDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Late this afternoon and early evening... MVFR/IFR ceilings and visibilities with light snow through the remainder of the afternoon. A brief burst or two of moderate snow not out of the question with LIFR visibilities. Winds under 10 knots but runways could become slick and snowcovered. A few inches at all TAF sites likely. High confidence. Tonight...Gradual improvement to VFR after snow moves northeast of the area by late evening. Westerly winds around or under 10 knots. high confidence. Sunday: VFR, Westerly winds in the afternoon of 10-15 knots with gusts to 25 knots at times. High confidence. OUTLOOK... Monday...VFR. West wind. High confidence. Monday night...Restrictions psbl in areas of rain or snow. Average confidence. Tuesday...Mainly VFR with a possible rain or snow shower north. Afternoon Winds becoming west and gusting 25-30 kt. High confidence. Tuesday night and Wednesday...VFR WIND with flurries or snow showers possible e PA and nw NJ. West-northwest gusts 35 kt with isolated 40 kt possible, especially Wednesday. High confidence. Thursday...VFR conditions expected. Average confidence.
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&& .MARINE...
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SCA is now in effect through Sunday for the ocean and Delaware Bay. Seas will continue to build this afternoon and evening. The pace indicated is based on obs which have been faster than the wavewatch guidance this afternoon. While a lull in the winds may occur tonight, westerly wind gusts over 25 knots are likely at several intervals through Sunday. Visibilities may be reduced in rain (mixed precip close to the coast) through the evening. OUTLOOK... Monday...Sub-SCA with fair weather. West wind. Mon night..Rain or snow likely and sub-SCA. Tuesday...SCA probable with increasing west winds and building seas. Tuesday night and Wednesday...Gale northwest wind 35-40 kt gusts as the coldest air of the season arrives. Wednesday night...Gales diminishing to SCA conditions. Thursday...Sub-SCA expected.
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&& .CLIMATE...
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Record daily snowfalls for the date are listed below for Saturday December 9. Note...compaction and melting on contact may limit amounts below our forecast in some of our forecast area. ACY 3.5-1933 PHL 2.9-1942 ILG 5.0-1928 ABE 9.1-2005
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Winter Weather Advisory until 1 AM EST Sunday for PAZ070-071- 101>106. Winter Weather Advisory until 7 PM EST this evening for PAZ060>062. NJ...Winter Weather Advisory until 1 AM EST Sunday for NJZ001- 007>010-012>022-025>027. Winter Storm Warning until 1 AM EST Sunday for NJZ023-024. DE...Winter Weather Advisory until 1 AM EST Sunday for DEZ001-002. Winter Weather Advisory until 7 PM EST this evening for DEZ004. Winter Storm Warning until 1 AM EST Sunday for DEZ003. MD...Winter Weather Advisory until 1 AM EST Sunday for MDZ008-012- 015-019-020. MARINE...Small Craft Advisory until 5 PM EST Sunday for ANZ430-431- 450>455.
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&& $$ Synopsis...AMC Near Term...Gaines Short Term...Gaines Long Term...AMC Aviation...AMC/Gaines Marine...AMC/Gaines Climate...

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