Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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955 FXUS61 KPHI 180818 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 318 AM EST Thu Jan 18 2018 .SYNOPSIS...
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High pressure will build across the Gulf coast through the end of the week, then offshore over the weekend. An area of low pressure will move across eastern Canada over the weekend as a back door cold front approaches from the north. Another area of low pressure will move through the Great Lakes Monday night into Tuesday, pulling a cold front across the area. High pressure will build toward the area late Wednesday into Thursday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Surface low pressure off the Mid-Atlantic coast continues to lift out to sea today as surface high pressure over the Lower Mississippi Valley slowly builds east. Meanwhile, closed H5 low over the Carolina coast tracks east as upper ridging builds into the Appalachians. For the local area, can expect a mostly sunny day as subsidence associated with the upper level ridging builds east. Pressure gradient tightens in the afternoon, and W-NW winds will increase to around 15 mph with 20-25 mph gusts. Airmass moderates over the area as 850 mb temps rise to 0 to +4C, resulting in highs in the mid 20s in the Poconos, and otherwise mostly in the low to mid 30s. Highs in the southern portion of the Delmarva will be near 40.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM FRIDAY/...
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High pressure continues to build east tonight. Pressure gradient slackens, and winds become light and variable. A weak upper disturbance passes well north of the area tonight, and this may bring some mid and upper clouds to the Poconos and NW NJ. Otherwise, skies will be mostly clear. As a result, can expect strong radiational cooling conditions for the Lehigh Valley, northern NJ, and the Pine Barrens of southern NJ. Lows tonight will range from the teens to lower 20s.
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&& .LONG TERM /FRIDAY THROUGH WEDNESDAY/...
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Quiet weather for the end of the week into the the weekend, with a return of unsettled weather for early next week. Dry conditions will continue for Friday into Saturday as high pressure builds to our south across the Gulf coast states through Friday, then offshore Saturday. Our area will remain on the northern periphery of the high which will keep a dry, west to southwest flow across the area. On Sunday, a back door cold front will sag toward our area from the north as an area of low pressure slides eastward across eastern Canada. Sunday should remain dry, but as we move into Sunday night and Monday, the back door frontal boundary is forecast to make its way across a portion of the area. As it does so, there will be some enhanced moisture and lift moving overtop of the front. This may lead to some light rain developing across the area Sunday night into Monday. It is possible that temperatures could drop below freezing across portions of northern New Jersey and northeastern Pennsylvania, possibly leading to some light freezing rain. Then Monday night into Tuesday morning, a cold front is expected to sweep across the area as an area of low pressure moves through the Great Lakes region. This will lead to a period of rainfall overnight Monday into Tuesday. It is possible that the rain could change over to snow across northern New Jersey and northeastern Pennsylvania before the precipitation ends Tuesday morning behind the cold frontal passage. For Tuesday night into Wednesday, the low pressure system moves across eastern Canada, while a secondary cold front moves toward the area from the west, which may cross the area during the day. Most of the area will remain dry, but there my be enough moisture across the northern areas as a short wave/vorticity impulse moves through for some snow showers to get squeezed out across portions of northern New Jersey and northeastern Pennsylvania.
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&& .AVIATION /08Z THURSDAY THROUGH MONDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR/SKC. NW winds 10-15 KT with gusts up to 20 KT, except for KPHL/KACY, where gusts up to 25 KT are possible. Tonight...LGT/VRB winds. SKC. OUTLOOK... Thursday through Saturday night...VFR. West to southwest winds; winds may gust 15-20 knots at time. High confidence. Sunday night-Monday...Conditions may lower to MVFR overnight Sunday into Monday, possibly IFR for northern areas, with a chance of showers. Gusty southeast winds 15-20 knots. Moderate confidence.
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&& .MARINE...
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Today...Will issue a Gale Warning for the DE ocean waters and Lower DE Bay as wind gusts have increased to around 35 KT. This should be brief, lasting through this morning. For the DE ocean waters, a SCA will be needed after the Gale Warning ends. Otherwise, Small Craft Advisories will continue for Upper DE Bay through this morning, and for the ocean into this evening. Wind gusts on the ocean may diminish a bit later this morning before picking up again in the afternoon. Tonight...SCA conditions end on the ocean this evening, and gusts to 20 KT will continue. Seas will diminish to 2-4 feet. On DE Bay, tranquil conditions. OUTLOOK... Friday-Friday night...Conditions expected to be below advisory levels, but winds may periodically gust around 20 knots. Saturday-Saturday night...Winds may approach Small Craft Advisory levels across the northern half of the Atlantic coastal waters. Sunday-Monday...Conditions expected to be below advisory levels, but winds may periodically gust around 20 knots.
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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 Friday for ANZ450>453. Gale Warning until 10 AM EST this morning for ANZ431-454-455. Small Craft Advisory until 10 AM EST this morning for ANZ430.
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&& $$ Synopsis...Robertson Near Term...MPS Short Term...MPS Long Term...Robertson Aviation...Robertson/MPS Marine...Robertson/MPS

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