Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 201432 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 932 AM EST Sat Jan 20 2018 .SYNOPSIS... High pressure centered well to our south today expands northward some tonight and Sunday before moving offshore. As low pressure moves across eastern Canada through tonight, a weak cold front settles southward across our area late tonight and Sunday. Another area of low pressure will move through the Great Lakes Monday night into Tuesday, pulling a cold front across our area. High pressure will then build toward our region late Wednesday through Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... For the 930 AM update, made some adjustments to the hourly temperature and dew point grids based on trends. Temperatures are climbing faster this morning especially across parts of the coastal plain, and the winds were adjusted up some especially closer to the coast and the higher terrain of the southern Poconos. A band of high level clouds continue across mostly the northern and western areas associated with an upper-level jet streak. Otherwise, surface high pressure is centered over the Southeast U.S. Low pressure passing through southern Canada will drag a weak surface trough through the region this afternoon. Zonal flow aloft will keep Arctic air in Canada. Heights and 1000-500 mb thicknesses will rise through the day, and southwest to west winds will gust to around 25 mph at some places. Given the warming aloft will translate to milder air at the surface. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... High pressure remains in control. Cirrus clouds will increase as some weak mid-level shortwave energy passes through the region. This will limit radiational cooling tonight, and much warmer temperatures can be expected. Lows will range from the mid 20s to the low 30s. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Unsettled weather for early next week, followed by quiet weather again for the middle to end of next week. On Sunday, a back door cold front will sag toward our area from the north, and is expected to sink across the area Sunday night. Sunday is expected to remain dry for now, but clouds will be on the increase through the day. As moisture increases overnight, there may be some lift moving overtop of the front. This may lead to some light rain/drizzle developing across the area Sunday night. Temperatures are expected to drop below freezing for portions of northern New Jersey and northeastern Pennsylvania as some cold air gets dammed up. If any precipitation does occur, this could lead to some light freezing rain or drizzle overnight Sunday. On Monday, low pressure will be moving through the mid- Mississippi Valley. As this happens, the frontal boundary across the area will try to lift northward as a warm front, but will likely not make much progress as it remains dammed up across the area. On Monday morning, there will likely remain some cold air across the northern areas north of the boundary, so there could remain some light freezing rain/drizzle. South of the front, dry conditions will likely move back in and some clearing may take place. Overnight Monday 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 moderate to heavy rainfall overnight Monday into Tuesday. Guidance is showing the potential for some weak instability with in the warm sector across southern New Jersey and Delaware and Maryland. For now we will not include thunderstorms, and wait until there is a greater potential. Dry air will move in behind the cold front during the afternoon. Winds will become gusty 20 to 25 mph behind the front as well. For Tuesday night into Wednesday night, 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, as any precipitation is forecast to remain to our north. If there is any precipitation, it would most likely occur across portions of northern New Jersey and northeastern Pennsylvania. Gusty conditions are expected on Wednesday as winds will be gusting at least 25 to 30 mph. High pressure returns for Thursday and Friday, leading to dry conditions. Winds will be less gusty than Wednesday, around 15 to 20 mph. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Rest of today...VFR with some clouds at or above 20,000 feet. West- southwest winds around 10 knots with some gusts to about 20 knots. Tonight...VFR with clouds at or above 20,000 feet. Winds becoming light and variable at most terminals. OUTLOOK... Sunday-Monday...Sub-VFR conditions expected, especially Sunday night and Monday. Lowest conditions across ABE, RDG, and TTN, which may drop to IFR. Improving conditions possible for ACY and MIV later Monday. Light rain or drizzle possible across northeast Pennsylvania and northern New Jersey. West winds may gust 15-20 knots. Low to Moderate confidence. Monday night-Tuesday..Conditions lower to IFR everywhere with periods of rain associated with a frontal passage. Southeast winds become westerly behind the front and begin gusting 25-30 knots. Moderate confidence. Tuesday night-Wednesday...VFR. Northwest winds, becoming gusty 25-30 knots during the day Wednesday. && .MARINE... Today...Winds and seas should stay below SCA levels for DE Bay, DE coastal ocean waters and far southern NJ coastal waters, though gusts around 20 kt are possible. For central and northern NJ coastal waters, a SCA remains in effect for today for wind gusts to 25 kt. Tonight...West winds gusting to 20 kt for the northern NJ coastal ocean waters. Otherwise, west winds 10 kt or less. OUTLOOK... Sunday-Monday...Conditions expected to remain below advisory levels, but winds may periodically gust around 20 knots. Monday night...Conditions expected to return to Small Craft Advisory levels. Tuesday-Wednesday...Small Craft Advisory level wind continue, but may reach gale force. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ450>452. && $$ Synopsis...Gorse/Robertson Near Term...Gorse/MPS Short Term...MPS Long Term...Robertson Aviation...Gorse/Robertson/MPS Marine...Robertson/MPS is the U.S. government's official web portal to all federal, state and local government web resources and services.