Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 020823 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 323 AM EST Fri Dec 2 2016 .SYNOPSIS...
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Low pressure will continue to move slowly into and across the Canadian Maritimes today into Saturday. High pressure over the Ohio Valley Saturday will move into our area Sunday before slowly shifting north and east later Monday into Tuesday. Low pressure will then consolidate from the Plains to the Great Lakes Tuesday into Thursday, sweeping a strong cold front across our area later Thursday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... Through sunrise... patch of clouds over the Delmarva is unexplained and slowly dissipating. Otherwise...mostly clear with a west wind. Today... A sunny or mostly sunny day south but considerable cloudiness develops ne PA and nw NJ with midday heating. Chance of flurries in the Poconos later today or this evening per the 500 mb vort lobe swinging sewd from Quebec. BTV snow squall parm has small indicator of snow shower potential far ne PA. Temps/winds were a blend of the 00z/2 GFS/NAM MOS. Raised guidance temps 1-2F per the EC 2m 18z temp of 49F at PHL. These fcst temps are a deg or two above normal. Winds should become gusty 20-25 mph midday or this aftn. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
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Clear to Partly cloudy except plenty of clouds nw edge of the fcst area from lake effect and still a chance of flurries in the Poconos. West-northwest wind a bit stronger than what it was predawn today. Fcst was a 50 50 blend of then 00z/2 GFS/NAM MOS. Resultant fcst lows are a couple degrees warmer than normal.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/...
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The synoptic setup starts with a closed low centered near the Canadian Maritimes early Saturday that then shifts eastward. This will maintain a northwest flow of colder air across our area. Some ridging them arrives Sunday allowing surface high pressure in place, however a short wave trough sliding across the Great Lakes will generally glance our area Sunday night into Monday. A more significant short wave slides up the Ohio Valley Monday night and Tuesday, driving surface low pressure with it. The pattern then loads up to our west with a significant trough taking shape. This should drive a consolidating low pressure system into the Great Lakes Wednesday and Thursday, with an associated strong cold front arriving in our area later Thursday. We used a model/continuity blend Saturday through Sunday night, then blended in the 00z WPC Guidance. Some adjustments were then made following additional collaboration with our neighboring offices. For Saturday and Sunday...An upper-level trough loosens its grip on the Northeast as the parent closed low weakens some and shifts east of the Canadian Maritimes. This allows a ridge to arrive on Sunday along with surface high pressure building in overhead. For Saturday however, continued cold air advection in combination with strong northwesterly flow will promote a gusty surface wind. The forecast soundings overall show enough steepening of the low-level lapse rates to result in wind gusts to around 30 mph during the day. These winds are expected to diminish later in the afternoon and especially at night as high pressure begins to build in. Lingering cyclonic flow and cold air advection should result in areas of stratocumulus Saturday especially across the northern half of the area. There could be some snow showers or flurries in the Poconos Saturday before enough subsidence and drying builds in. The clouds then increase Sunday, especially later in the day and at night as a weakening short wave trough moves through at night. This feature may have a split area of light QPF, one across the north closer to the main forcing and one southward with a weak surface low. Overall, there looks to be a low chance for some rain/snow showers across parts of the area, however any amounts are expected to be rather light. For Monday and Tuesday...A weakening short wave trough slides just to our north Monday with perhaps some morning light rain/snow showers in parts of the area. Some ridging then builds eastward, however the orientation of it will position surface high pressure to our north although it looks to build down into our area for a time Monday night into Tuesday. As a trough starts to sharpen across the Western states, an initial short wave that could be robust ejects northeastward from the Gulf Coast states late Monday. This feature is forecast to move into our area Tuesday, however it should be running into surface high pressure and ridging aloft to our north. The model guidance generally brings a precipitation shield up unto our area Tuesday, however an associated surface low may then be deflected eastward out to sea along a developing baroclinic zone. This occurs as a weakening surface low lifts into the eastern Great Lakes. Overall, Tuesday is looking more and more unsettled across much of the area however the northern extent of the precipitation is in question given drier air and the influence of surface high pressure. As a result, we increased the PoPs into the likely range down across the south with these then decreasing some northward. If precipitation gets into the northern areas fast enough, snow or mixed precipitation could occur for a time. The surface low to our south and high pressure to the north will result in some increase in an onshore flow. For Wednesday and Thursday...The energy that moves into the area Tuesday should be weakening Wednesday as surface low pressure moves away from the Mid Atlantic coast. High pressure centered to our north will keep cool air in place and lots of clouds may linger Wednesday. A significant trough across the West starts to move into the Plains Wednesday with surface low development and consolidation occurring. This will set the stage for downstream warm air advection and some ridging, with a warm front approaching our area. The main surface low is forecast to track to our northwest Thursday and it may occlude, keeping the warm front from crossing our entire area. The amount of overrunning that materializes will determine how much precipitation occurs Wednesday night and Thursday ahead of the cold front, however deeper moisture from the Gulf should get pulled north ahead of the front with the potential for another round of much needed rain for our area. The passage of an associated strong cold front later Thursday will mark the beginning of a much colder airmass.
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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. Through today... VFR few clouds aoa 4000 ft. light west wind before sunrise becomes gusty 20-25 kt midday and this afternoon. Tonight...clear or sct clouds aoa 4000 ft. West-northwest wind may be gusty to 15 kt. OUTLOOK... Saturday and Sunday...VFR overall with clouds increasing later Sunday. Some light rain/snow showers possible later Sunday night, with perhaps a brief period of MVFR ceilings mainly for RDG, ABE to TTN. Northwest winds increasing to 15 to 20 knots with gusts to around 25 knots Saturday, then diminishing to 10 knots or less Saturday night and Sunday. Monday and Tuesday...A brief period of MVFR ceilings possible mainly at RDG, ABE and TTN early Monday with some light rain/snow showers, Otherwise VFR. VFR ceilings Monday night may lower to MVFR/IFR Tuesday with some rain overspreading the area. This could start as some snow from around ABE northward.
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&& .MARINE...
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SCA continues for lower DE Bay but also the Atlc waters. Appears guidance is running a little low and has been for the past 18 hours. Surface and boundary layer temps at or below the SST permitting decent transfer, at least in the lowest 25 to 50 MB adjacent the sfc. Winds may lull for a few hours midday. Isolated gale force northwest wind gusts possible late tonight in lower De Bay. OUTLOOK... Saturday...Gale Watch issued for the day Saturday for all but the Upper Delaware Bay (Small Craft Advisory issued here). Continued cold air advection and 925 MB flow of 30-35 knots will combine with steepening low-level lapse rates. There may be some enhancement within the northwest flow down Delaware Bay (lower part) and into the adjacent Atlantic coastal waters. Since there is the potential for a period of low-end gale force gusts in combination with some local enhancement, a Gale Watch has been issued. The winds should subside some Saturday night as high pressure starts to build in. Sunday and Monday...The conditions should be below Small Craft Advisory criteria as high pressure generally dominates. Tuesday...Low pressure moves into the area. This combined with high pressure to the north should result in an increase in the winds, with gusts to about 25 knots possible. An onshore flow should also lead to seas building to and above 5 feet on the ocean zones. A Small Craft Advisory looks to be needed.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Gale Watch from Saturday morning through Saturday afternoon for ANZ431-450>455. Small Craft Advisory until 6 AM EST Saturday for ANZ431- 450>455. Small Craft Advisory from noon today to 6 PM EST Saturday for ANZ430.
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&& $$ Synopsis...Gorse Near Term...Drag Short Term...Drag Long Term...Gorse Aviation...Drag/Gorse Marine...Drag/Gorse

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