Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 170547 AFDOKX Area Forecast Discussion National Weather Service New York NY 1247 AM EST Sun Dec 17 2017 .SYNOPSIS... High pressure builds in through Sunday. A series of weak frontal systems then move through the region from Sunday night through midweek, before high pressure builds in late in the upcoming work week. A frontal system approaches by the start of next weekend. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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Forecast remains on track. Made adjustments to the temperatures and dew points for current conditions and trends. Northern stream ridging begins to build in overnight, allowing for clearing overnight, especially across the eastern half of the region. Lingering moisture between 5 and 10 thousand feet may keep the western half of the region at least partly cloudy.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/...
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Another unseasonably chilly day is forecast on Sunday as high pressure settles over the Tri-State. Shortwave energy will fast approach from the west on Sunday within zonal flow aloft. This energy currently resides over Mexico and will lift towards the Plains tonight and get caught in the zonal flow on Sunday. The shortwave energy will dampen out as it approaches, but there will be enough moisture to increase clouds through day. The main concern on Sunday night will be surrounding any precipitation that develops with warm advection as the weakening shortwave energy moves overhead. Models differ in whether there will be any measurable precipitation due to overall weak lift. There will be a warm front approaching, which may be just enough along with the warm advection to produce light precipitation. Temperatures profiles are questionable, but there are signals of a warm nose developing around 900-950 mb Sunday night. This may be able to change any snow to freezing rain or rain. Surface temperatures away from the NYC metro and coast will likely remain below 32 degrees, so will need to watch for any freezing rain. For now, PoPs are capped at 30 percent and will show a chance for snow inland and a mix of snow, freezing rain, or rain near the coast. Any snow inland could change to a mix towards day break as the warm nose attempts to advance north.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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Models continue in good agreement with a fairly progressive upper pattern in place through the week, with a series of weak frontal systems moving through the region Sunday Night through midweek as a muted northern stream longwave trough slides from the Great Lakes into the Northeast. First system of note continues to be for Sunday Night into Monday morning as the closed low currently over NW Mexico shears towards the NE ahead of a developing Western US trough. General agreement in this energy being significantly weakened as it approaches the region with limited moisture, but potential exists for a light precip event Sunday night into Monday morning. Thermal profiles suggest a start as snow or wintry mix, quickly transitioning to rain for NYC/LI as boundary layer sufficiently warms, but remaining a wintry mix to the N and W of NYC/LI into Monday morning with a subtle warm nose but likely freezing surface temps. Although precip amounts are expected to be light, potential exists for hazardous (icy) travel N&NW of NYC/LI for Monday morning commute. Thereafter, models in fairly good agreement with the broad but shallow northern stream trough approaching the NE on Tuesday and sliding through during the midweek. At the surface, the primary low pressure system rides through Quebec/Ontario with trailing cold front approaching the region Tue, and crossing Tue Night. Not expecting much precip during this time period, due to best forcing north of the region, and limited moisture being drawn north in split flow. Thermal profiles suggests precip would be mainly liquid, but if anything develops in the waa pattern Monday Night into Tue morning there would be a threat for freezing rain across interior as cold air typically has a tough time scouring out in this setup. Upper trough swings through the NE Tue Night into Wed with a glancing shot of modifying arctic air in the wake of the cold front for Wed. Upper flow flattens and even becomes a bit ridged for Thursday ahead of the next northern stream trough digging into the Upper Plains. At the surface, high pressure builds in from the west Wed and across Thu, with dry and seasonably cold conditions. Models in general agreement with a pattern shift to a more longitudinally oriented upper flow heading into the weekend, as several pieces of northern stream energy begin to dig a deep longwave trough into the Western/Central US. This may bring the coldest air of the season into the Central US by around Christmas. Meanwhile, energy rounding this trough appears to send a frontal system through the region during the Fri Night- Sat Night time period.
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&& .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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High pressure builds over the area into tonight. VFR through the TAF period. 3500-5000 ft ceilings are possible through around 7-8Z and then again this evening. NW-NE winds early this morning, with speeds falling below 10 KT throughout, and all but KJFK/KLGA/KEWR becoming light and variable. Winds become light and variable throughout by early afternoon. .OUTLOOK FOR 06Z MONDAY THROUGH THURSDAY... .Late tonight-Mon morning...MVFR or lower possible in light snow, transitioning to a wintry mix. .Mon aftn-night...low chc MVFR in any rain and/or snow showers. .Tue-Tue night...MVFR or lower possible. W- WSW winds G20-30KT possible. .Wed-Thu...VFR. NW winds G20-30KT probable Wed/Wed night.
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&& .MARINE...
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Winds and seas have subsided below small craft levels on the ocean waters west of Moriches Inlet, while sea remain above 5 feet east of Moriches Inlet. Have therefore cancelled the small craft to the west of Moriches Inlet. Seas may also, remain above 5 ft east of Moriches inlet into the daylight hours on Sunday morning. A weak pressure gradient Sunday through Monday Night will lead to sub-SCA conditions. The next chance for SCA conditions will be late Tuesday/Tue eve in SW flow ahead of approaching cold front, with high likelihood of widespread SCA Tuesday Night through Wednesday with tight pressure gradient and strong caa in wake of cold front. Marginal gale gusts are possible during this time frame. Conditions then should fall back below SCA heading into Thu as high pressure builds towards the waters.
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&& .HYDROLOGY... No significant hydrologic impacts expected. && .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...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 6 AM EST early this morning for ANZ350.
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&& $$

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