Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 132016 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 416 PM EDT Tue Mar 13 2018 .SYNOPSIS... Strong low pressure east of New England will move north into the Canadian Maritime area and then remain near the lower St. Lawrence Valley through Saturday. Meanwhile high pressure will extend south from Canada across the Great Lakes and Ohio Valley, maintaining a relatively cold northwest flow across our mid- Atlantic region into the weekend. Another coastal may develop in the early to middle part of next week, but as of now its track, timing and intensity are quite uncertain. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Intense coastal low south and east of Cape Cod will lift into the Canadian Maritimes tonight. Meanwhile, closed H5 low over the Great Lakes tracks to the south and east and will be just north of NYC by daybreak Wednesday. Clouds scatter out this evening, and any lingering snow showers over the southern Poconos will taper off. Winds diminish shortly after sunset. Temperatures then drop off fairly quickly in the evening due to the combination of clearing skies, diminishing winds, and CAA. Lows tonight will generally drop into the 20s, except for around 30 in Philly. Shortwaves approach the region late tonight as that 500 mb low tracks east. Temperatures may hold steady late tonight and into daybreak due to the increased cloud cover. Some snow showers associated with the low will move into the southern Poconos and far northwest NJ prior to daybreak, but any snow accumulations will be light. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... Westerly pressure gradient tightens up between low pressure retrograding through the Canadian Maritimes and high pressure over the Gulf Coast states. Meanwhile, several potent shortwaves will pass through the region in the afternoon, and there will be enough instability to touch off rain and/or snow showers south and east of the Fall Line, and more widespread snow showers in the southern Poconos, Lehigh Valley, and northwest NJ. Snow accumulations will generally be up to an inch in the heavier snow bands in the Poconos, otherwise, generally 1/2" snow elsewhere. Highs should get into the lower 40s for most of southern NJ and southeast PA, so would not expect much in the way of accumulation. West winds increase to 15-20 mph with 25-35 mph gusts in the afternoon. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... For the long-term period starting Wednesday night, the mid- Atlantic region remains largely under the influence of an upper low/trof over eastern Canada and the northeast U.S. This pattern will be associated with NW flow aloft and gernerally below normal temps, especially if the ECMWF guidance is to be believed. On Thursday a shortwv trof is fcst to rotate around the main upper low and across the mid-Atlantic region, with an associated cold front also crossing the area. This along with some low- level instability may trigger some rain or snow showers during the afternoon. At this time we are carrying only chance or slight chance PoPs. On Friday it will be colder behind the cold front, and another shortwv is fcst to rotate through. There seems to be a bit less instby and sfc reflection with this one and any snow showers will likely be confined to the southern Poconos. For the weekend the upper low remains invof Canadian Maritimes. Temperatures are forecast to be a bit milder but still a few degrees below normal. A back door cold front may push through on Sunday but no assocd precip is expected. Temps will becomed colder again for Monday and Tuesday as high pressure builds in from the NW. Models are forecastin another low to develop off the mid-Atlantic coast around mid week, but whether it will track along the coast or move out to sea is unclear. && .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Tonight...VFR. West winds diminishing to less than 10 kt this evening. Wednesday...VFR. Scattered snow showers may impact KABE/KRDG, and scattered rain and/or snow showers may briefly impact KTTN/KPNE/KPHL. Best chances at KABE/KRDG. Brief MVFR conditions possible. West winds increase to 15-20 KT with 25-35 kt gusts late Wednesday morning. Outlook... Thursday...Mostly VFR. Occasional MVFR possible in snow or rain showers during the day, more likely at ABE/RDG. Westerly winds gusting to 20-25 knots. Moderate confidence. Friday...Mostly VFR. Northwest winds gusting to 20-25 knots. High confidence. Saturday and Sunday...VFR. Northwest winds gusting 15-20 knots on Saturday. High confidence. && .MARINE... Wind gusts have diminished below gale force, so Gale Warnings were cancelled and Small Craft Advisories are now in effect. For DE Bay, SCA is in effect through this evening, and a new SCA will be needed for Wednesday. For the ocean, expecting gusts to 30 kt tonight and into Wednesday. Based on latest trends, have pushed back the start of the Gale Watch on Wednesday until the evening. In its place, a SCA is now in effect tonight through Wednesday. Outlook... A gale watch is in effect for Wednesday night. SCA conditions may persist through Thursday and Friday with gusty NW winds. Sub SCA condition are expected for Saturday and Sunday. && .TIDES/COASTAL FLOODING... Surface flow will increase on Wednesday from the west, which is an offshore flow. This will limit the threat of flooding with subsequent high tides. However, confidence is a little lower on the NJ coast where surge will be higher, so coastal flooding cannot be ruled out for the high tide this evening. However, the astronomical tide will be lower for the evening high tide, likely limiting the threat. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Gale Watch from Wednesday evening through late Wednesday night for ANZ430-431-450>455. Small Craft Advisory until 6 PM EDT Wednesday for ANZ450>455. Small Craft Advisory until 7 PM EDT this evening for ANZ430- 431. && $$ Synopsis...AMC Near Term...MPS Short Term...MPS Long Term...AMC Aviation...AMC/MPS Marine...AMC/MPS Tides/Coastal Flooding...MPS is the U.S. government's official web portal to all federal, state and local government web resources and services.