Area Forecast Discussion
Issued by NWS Upton, NY

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299 FXUS61 KOKX 162041 CCA AFDOKX Area Forecast Discussion...CORRECTED National Weather Service New York NY 341 PM EST Sat Dec 16 2017 .SYNOPSIS... A cold front moves south of the area this evening and will be followed by high pressure for Sunday. A series of weak frontal systems then move through the region Sunday night through midweek, before high pressure builds in for the late week. A frontal system approaches by the start of the weekend. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Cold front resides across northern New England this afternoon, and will continue to sink south through the evening hours as a shortwave and associated vort max pass to our northeast. Latest high resolution model data hints at some snow showers in a banded structure moving south along the cold front this evening. The front should be able to provide extra surface convergence in combination with the passing energy to our northeast. Will have to watch trends as the front nears as any heavier burst of snow could put down a quick dusting. Do not anticipate anything widespread, and have limited PoP to slight chance. Clearing skies should follow overnight behind the front passage, 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. Lows will range from the teens inland to the lower and middle 20s closer to the coast. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... 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. No precipitation is expected with highs in the lower and middle 30s. 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. && .LONG TERM /MONDAY THROUGH FRIDAY/... 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. && .AVIATION /21Z SATURDAY THROUGH THURSDAY/... A cold frontal passage occurs this evening. Ceilings around 3500 ft can generally be expected through the TAF period for the city terminals, coastal Connecticut and Long Island. To the north however, there is a higher probability for ceilings to settle around 3000 ft for this afternoon and evening. MVFR has therefore been forecast for those areas. There is a slight chance for snow showers through approximately 00Z. VCSH have been included in the TAFs, with coverage expected to be mainly isolated at this time. Winds in the 250-270 true range will veer to the northwest behind the cold front tonight. The winds will continue to veer to the north on Sunday. .OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY... .Rest of Sunday...IFR possible overnight with snow or a light wintry mix possible. Variable wind direction with speeds below 10 kt. .Monday...Light rain possible along the coast in the morning, with a light wintry mix possible elsewhere. Becoming VFR. Westerly flow developing. .Tuesday...Areas of MVFR possible with southwest flow. .Wednesday...VFR with northwest flow 20-25 kt. .Thursday...VFR with light winds becoming southerly. && .MARINE... Small craft advisory remains in effect on the near shore waters until 7 pm as gusts 25 to 30 kt continue. The advisory remains in effect on the ocean into the overnight as seas will remain elevated. The winds will diminish overnight on the ocean, but seas will remain elevated and may remain above 5 ft east of Moriches inlet through Sunday morning. Have extended the advisory on those waters until 6 am Sunday. A weak pressure gradient Sunday and Sunday night will lead to sub-SCA conditions. Sub SCA conditions expected Monday into Monday Night with a weak pressure gradient over the region. 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. && .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... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ330- 335-338-340-345. Small Craft Advisory until 1 AM EST Sunday for ANZ353-355. Small Craft Advisory until 6 AM EST Sunday for ANZ350. && $$ SYNOPSIS...DS/NV NEAR TERM...DS SHORT TERM...DS LONG TERM...NV AVIATION...12 MARINE...DS/NV HYDROLOGY...DS/NV EQUIPMENT...

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