Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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409 FXUS61 KPHI 090908 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 408 AM EST Fri Dec 9 2016 .SYNOPSIS...
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An area of low pressure will continue to slowly drift to the south of Greenland through the weekend. With high pressure to our west, a strong west to northwest flow will remain through Saturday . High pressure briefly affects the area Saturday night, then moves offshore Sunday. A warm front is expected to lift across the area Sunday night into Monday, before an area of low pressure is forecast to move north of the area Monday. This system will then pull a cold front across the area Monday. Another frontal boundary is expected to move across the area Tuesday night or Wednesday, and a coastal low may develop along this frontal boundary Wednesday. A strong west to northwest flow is expected to develop by the end of the week as high pressure tries to build in from the west.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Another day of strong northwesterly flow resulting in breezy conditions and below normal temperatures. Highs (mostly 30s to near 40 across the region) will be around 5 degrees lower than yesterday, which will be 5 to 10 degrees lower than normal. Higher elevations in the Southern Poconos may not get out of the 20s. Snow showers, a result of the strong northwesterly flow/cold air advection/lake effect, could propagate as far se as the southern Poconos. However, a dry boundary layer has thus far kept any precip from reaching the ground in our area, and by this afternoon low level flow should become weaker, so the window of opportunity is closing. If any snow showers do make it to our region by mid day, snow accumulations should be near or below one half inch (note: the storm total snow graphic is now for the Sunday night event since that looks to be a potentially bigger impact event).
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
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Surface high over the Ohio Valley tries to build west. As a result, the pressure gradient relaxes resulting in the winds dropping off. However, this doesn`t mean that we will have a milder night temperature wise. If anything, we should be a bit colder tonight (generally in the 20s, teens in the Poconos and NW NJ).
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/...
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On Saturday, there will be fairly steep lapse rates combined with some enhanced moisture across the far northern tier of the area. With the west-northwest flow remaining across the area, there could continue to be isolated lake snow showers/flurries developing which could make their way across our area. We will keep flurries/sprinkles for the middle part of the area as well as the short wave passes just to our north. High pressure briefly affects the area Saturday night, providing dry conditions. Saturday will remain cold and windy, although winds are not expected to be as high as Friday. 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 north of the advancing warm front to our south. If any precipitation develops during the day, temperatures should be cold enough for the northern half of the area to see snow, or at least a rain/snow mix. However, the best chance of precipitation looks to be Sunday night into Monday. A warm front is forecast to lift across the area late Sunday night and into Monday as an area of low pressure is forecast to move north of the area Monday. Conditions are expected to be cold enough overnight across the northern half of the area for snow to fall for a period of time. However, as the warm front lifts northward into the area, temperatures are expected to begin warming. This should help precipitation begin to transition into a wintry mix for the northern half of the area. It is possible that a period of sleet and freezing rain could occur across the northern areas as a chance over to rain occurs from south to north. The most likely area to recieve accumulating snowfall is expected to be the northern third of the area, although the middle third could get some light snow before changing over to rain. This change over would limit any accumulations. The southern third is expected to stay rain through the event. As the low continues to lift northward during the day, a cold front is expected to move across the area late in the day and overnight. Precipitation chances should diminish behind the cold front later in the day and overnight. Any precipitation overnight should change to snow for the northern half while the southern half would stay rain. High pressure may briefly affect the area Tuesday, but will quickly build offshore. Then a cold front is expected Tuesday night into Wednesday, which could bring another round of precipitation. The GFS and ECMWF have different timing with the front, as well as with a possible coastal low that could develop and move along this boundary. The GFS is slower, moving the front through Wednesday and the coastal low up the coast late on Wednesday. The ECMWF moves the front through Tuesday night, and moves the coastal low farther offshore and then out to sea. We will keep a chance of precipitation Tuesday night into Wednesday with the frontal passage and possible effects of the coastal low if it gets close enough. Even if the low remains offshore, we should get some precipitation from the front. Strong west to northwest flow is expected again by Thursday as high pressure tries to build in from the west. This is expected to usher in very chilly air along with the breezy conditions. There could again be a chance for isolated snow showers/flurries across much of the area Thursday.
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&& .AVIATION /09Z FRIDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR conditions are expected through the TAF period. Isolated rain/snow showers may approach KABE and KRDG between 15 and 21Z, but few visibility restrictions are expected and confidence that either TAF site will be affected is low. Otherwise, few to bkn mid level clouds (4000 to 6000 ft AGL) will be possible through the TAF period. Breezy west northwesterly winds continue through the day today, with winds dropping off beginning around 21Z. OUTLOOK... Saturday-Saturday night...Generally VFR. Isolated showers or flurries/sprinkles are possible across the northern half of the area during the day which may temporarily lower conditions. Gusty west to northwest winds 15-20 knots during the day. Sunday...VFR early, lowering to MVFR by the afternoon. Rain or snow possible late in the day. Sunday night-Monday...MVFR early, then IFR overnight into Monday. Rain or snow becoming likely. Accumulating snow possible for the northern third of the area, with a chance of freezing rain around daybreak. Rain/snow mix for central third of the area. Rain across the southern third. All precipitation likely to become all rain Monday. Winds could become gusty during the day Monday 20 to 25 knots. Monday night...Improving conditions overnight to VFR. Tuesday...VFR expected with west to northwest gusts around 15 to 20 knots.
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&& .MARINE...
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Earlier gale gusts at the mouth of the Delaware Bay have diminished. So have changed that gale warning to a small craft advisory as gusts near or above 25 kt will be possible through the day time hours today, and through the evening hours on the coastal waters. The strongest winds are expected on the coastal waters adjacent to northern and central NJ. We have already seen a few gusts right at gale force, so have converted part of the gale watch to a gale warning. Winds and seas should begin to diminish this evening, but may not drop below SCA until very late tonight. Saturday-Sunday...Conditions expected to remain below Small Craft Advisory levels, although winds could gust around 20 knots at times. Sunday night...Small Craft Advisory levels possible overnight. Monday-Monday night...Small Craft Advisory conditions likely, possibly reaching gale force for a period of time. Tuesday...Small Craft Advisory conditions remain possible.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 1 AM EST Saturday for ANZ452>455. Gale Warning until 6 PM EST this evening for ANZ450-451. Small Craft Advisory until 10 PM EST this evening for ANZ430- 431.
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&& $$ Synopsis...Robertson Near Term...Johnson Short Term...Johnson Long Term...Robertson Aviation...Johnson/Robertson Marine...Johnson/Robertson

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