Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 181151 AFDOKX Area Forecast Discussion National Weather Service New York NY 751 AM EDT Sun Mar 18 2018 .SYNOPSIS... Weak low pressure and cold front approach today and pass tonight. High pressure builds down from southern Canada through Monday night. A series of lows will pass to the south from Tuesday into Wednesday night, followed by high pressure building down from central Canada for the rest of this week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Upper shortwave passes from NW to SE across New England. Generally sunny skies and chilly temperatures are expected as cooler air moved in behind earlier cold frontal passage. Followed a MOS blend, expecting highs from the upper 30s to the lower 40s. A few gusts are possible during the day today adding to the chill. && .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/... Another upper level shortwave passes just to the north tonight as a weak area of low pressure and frontal boundary move through overnight. Very low probability for a few flurries, with operational GFS only model hinting at a few flurries. Mostly clear skies give way to partly cloudy conditions as these weak disturbances move through. High pressure builds from the north Monday, but remains centered in Canada as it is blocked by mid west shortwave tracking from west to east. During this time frame, mainly clear skies are forecast, along with chilly temperatures as cold Canadian air remains. Lows each night range from the upper teens to the lower 30s in NYC. During the day Monday, mos consensus forecasts a range from the upper 30s to middle 40s, which seems reasonable given cold temps aloft. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Very complex and uncertain scenario going into this time frame as multiple shortwave troughs interact to form a series of surface lows that could impact the area. Some of this energy will be coming from (1) the subtropical Pacific, (2) a cutoff low over the western CONUS, (3) another cutoff low farther west over the Pacific, and (4) additional shortwaves dropping down from central Canada. Complicating matters further will be the confluence of northern/southern streams situated over or just north of the area. Models are converging on a general solution of energy from (1) and (2) combining to help form an initial sfc low that should eject off the southern Mid Atlantic coast on Tuesday, then phasing of (3) and (4) to form a second stronger low that should also pass off the Mid Atlantic coast on Wed. Given model tendency (especially in the GFS) to overdo the confluence zone and suppress sfc lows too far south, also somewhat favorable coupling of two upper jet streaks, one associated with the confluence zone and another with the approaching western energy, think chances for snow could exist occur farther north with both rounds than operational model forecasts suggest, with the combo of the 00Z NAM/03Z SREF mean capturing this idea pretty well for the first low. With that in mind, have forecast chance PoP with the first wave for NYC metro and Long Island for daytime Tue, and then likely PoP for Long Island and chance elsewhere on Wed. Despite fcst high temps, sfc wet bulb temps should be cold enough to support all snow. One thing that remains fairly consistent regardless of solution is that it will be at least brisk to windy from late Tuesday into Thursday - potentially rather gusty depending on exact track/strength of the coastal low(s). The axis of the SE Canada cutoff passes to the east Thursday night, but with dry low levels, it should be dry. Friday and Friday night should be dry as northern stream ridging transits the area. For now went dry on Saturday as a cutoff low builds to the north, and it appears that the next batch of moisture/lift holds off until later in the weekend. Temperatures are forecast to be below normal. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/...
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High pressure will build to the north today. A weakening low will pass to the SW tonight. VFR. Winds should back NW today and increase to around or just over 10 kt, with gusts close to 20 kt generally between 15Z- 22Z. .OUTLOOK FOR 12Z MONDAY THROUGH THURSDAY... .Monday into Monday night...VFR. .Tuesday...Low confidence forecast through Wednesday. Chance of snow with IFR conditions for the Long Island and NYC Metro terminals. ENE winds G20KT NYC metro/coastal terminals. .Tuesday night...MVFR conditions possible with any lingering snow showers. NE winds G20KT NYC metro/coastal terminals, mainly late. .Wednesday...Snow with IFR conds likely at the Long Island terminals, and may also be possible farther north including all local terminals. NE winds G20-25KT. .Thursday...VFR. N winds G15-20KT.
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&& .MARINE... Earlier SCA has expired. Winds should increase by this afternoon as the pressure gradient tightens, with gusts up to 25 kt possible over the eastern waters. Will hold off on any headlines as 25 kt gusts should be brief, late afternoon. However, a short fused SCA is not out of the question if conditions look to be of longer duration. Winds do diminish tonight and into Monday as high pressure builds in from the north. Seas remain 4 ft or less on the ocean and 2 ft or less on non ocean waters through Monday night. However, cannot completely rule out 5 footers over the eastern ocean waters late in the day due to an increase in northerly winds. The pressure gradient should tighten Tuesday and remain moderate to strong in strength into Thursday. SCA conditions probably develop on the coastal ocean waters Tuesday and on the remainder of the waters Tuesday night. SCA conditions probably will continue into at least Wednesday night, with gales possible on the ocean from late Tue night into Wed evening. Conditions should gradually fall below SCA levels on Thursday. && .HYDROLOGY... A low probability for significant precipitation exists Tuesday through Wednesday night depending on the eventual track of low pressure centers. If precipitation does indeed occur, it likely will be in the form of snow, so no hydrologic impacts are anticipated. && .TIDES/COASTAL FLOODING... There is the potential for a prolonged period of E-NE flow from Monday night into Wednesday Night. Tidal departures of generally only 1 to 1 1/2 ft are needed for minor flooding for many locations during this time, and 2 to 3 ft for moderate. Depending on the exact track/strength of a coastal low or lows during this time frame, there is the potential for minor to moderate coastal flooding, but predictability on the details remains low. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...Goodman/PW NEAR TERM...PW SHORT TERM...PW LONG TERM...Goodman AVIATION...Goodman MARINE...Goodman/PW HYDROLOGY...Goodman/PW TIDES/COASTAL FLOODING... EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.