Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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523 FXUS61 KPHI 070140 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 840 PM EST Tue Dec 6 2016 .SYNOPSIS... High pressure over the northeast will give way to developing low pressure off the Carolinas into tonight. Meanwhile, low pressure nearing James Bay sends a cold front thru our area on Wednesday, sweeping the Carolinas low well offshore. The low pressure over James Bay will move to Atlantic Canada into Friday, while high pressure over the central United States moves into the middle Atlantic this weekend. A warm front may approach our region by Monday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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8:30 pm update: Low level cold air with temperatures near freezing on many mesonet obs is still ongoing from Northamptoncounty eastward toward Morris county. SPC mesoanalysis shows both the 925 MB 0C line and the 850 MB 0C line have already advected north of these locations. SO the precipitation will likely be freezing rain for the next few hours before temperatures slowly overnight. The winter weather advisory has expanded into portions of the Lehigh Valley and Northern New Jersey through 1am. 6:30 pm update: Brightbanding on radar coupled with numerous ground reports show sleet to be falling across many locations in the Lehigh valley, NW suburbs of philly and northern New Jersey. A minor accumulation of sleet was added to the forecast with this update for those locations. A spotter in Sussex county indicated that the elevation cutoff is about 900 feet for the snow/no snow cutoff in the areas that are expecting elevation dependent accumulating snows. Top amounts look to be slightly higher with a little more QPF in the forecast now, around 4 inches at Mount Pocono. An updated snow map was sent to our website. 3:30 main forecast: A double-barrel low pressure system is expected to combine energy off the Carolina coast this evening, then intensify before the system moves slowly northeast out over the Atlantic on Wednesday. Precipitation associated with this system has already overspread the CWA this afternoon, with a brief period of sleet reported on the leading edge. The atmospheric profile still looks conducive for snow in the far north (Carbon/Monroe/Sussex counties), especially in the higher elevations, and since current QPF guidance is similar to previous runs, 2 possibly up to 4 inches mainly above 1000 feet still looks plausible, with several hours of moderate snowfall possible in those areas this evening. The current Winter Weather Advisory will therefore continue through the overnight hours. Easterly winds this afternoon generally under 10 mph are expected to veer to the northeast during the overnight hours as the speed increases to around 15 to 20 MPH with higher gusts near the coast. Areas that see mainly rain (generally south of I-80) can expect around one- half inch of precipitation from this event, with light rain or drizzle after midnight.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... As the low continues to move out to sea, precipitation will end during the morning hours basically from southwest to northeast...and any remaining wind gusts (especially closer to the coast) will gradually diminish as the pressure gradient relaxes. Expect cloudy conditions in the morning...with gradual improvement from west to east as the day wears on. Northwest winds are expected around 10 MPH...perhaps slightly stronger along near the coast. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... Temperatures will continue to be mild on Thursday, ahead of an approaching cold front. Models are in better agreement backing off on precip for Thursday however will hold on to a slight chance of rain due to increasing moisture. The long wave trough and attendant cold front continues east, pushing the cold front across the the region late Thursday into Thursday night. High temperatures on Friday will be mainly in the 30s to lower 40s. A few snow showers occuring beneath the cold mid level trough and downstream from the Great Lakes may make it into the far northwest corner of the forecast area on Friday, mainly northwest of I-95-276-76 where the BTV Snow Squall Parameter values are the highest. Models are also in a little better agreement bringing precip in Sunday night into Monday. The cooler temperatures will continue into Saturday. Models are also in a little better agreement for early next week. bringing the next storm system across the region late Sunday into Monday. GFS thermal profiles support wintry precip initially with a changeover to rain Monday, while the slower ECMWF is much warmer, suggesting a primarily rain event. Given the antecedent cold air mass in place, wintry precip is plausible at the onset, with a changeover to rain. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. IFR conditions are still expected to become predominant through the evening hours at many TAF locations as bands of moderate rain move through. ..but no major problems are expected. Rain is expected to taper off from SW to NE late tonight, but low clouds will remain over the area through a good portion of the overnight hours, with lingering IFR conditions. NE winds around 10 kt with higher gusts closer to the coast are expected tonight. Northwest winds in the 5 to 10 KT range are expected on Wednesday as the low continues to move out to sea. A slow improvement to MVFR around noontime and VFR by sunset is currently expected. OUTLOOK... Predominantly VFR at all TAF sites through the period. Northwest winds may gust up to around 25 knots Thu night into Friday. && .MARINE... A Gale Warning continues for tonight for the coastal waters of DE and S NJ as well as the lower DE Bay as easterly winds strengthen to the north of the coastal low. A SCA continues for the northern coastal waters and for the upper DE Bay with gusts 25-30 kt possible tonight. 4-7 ft seas are expected in response to the strengthening wind field. Although northwest wind gusts are expected to remain below 25 knots on Wednesday, seas are forecast to remain elevated, at or above 5 FT. Thus, a Small Craft Advisory for hazardous seas may be needed for the ocean waters. OUTLOOK... Gusts over 25 knots from the northwest are likely Thursday night and Friday with some potential to reach gale force. Winds will decrease on Saturday below 25 knots from the northwest. Seas are likely to remain below five feet for the outlook period. && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...Winter Weather Advisory until 1 AM EST Wednesday for PAZ062. Winter Weather Advisory until 6 AM EST Wednesday for PAZ054- 055. NJ...Winter Weather Advisory until 1 AM EST Wednesday for NJZ007>009. Winter Weather Advisory until 6 AM EST Wednesday for NJZ001. DE...None. MD...None. MARINE...Gale Warning until 6 AM EST Wednesday for ANZ452>455. Small Craft Advisory until 6 AM EST Wednesday for ANZ450-451. Small Craft Advisory until 4 AM EST Wednesday for ANZ430. Gale Warning until 4 AM EST Wednesday for ANZ431.
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