Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 152344 AFDOKX Area Forecast Discussion National Weather Service New York NY 644 PM EST Fri Dec 15 2017 .SYNOPSIS... Low pressure will move off the Middle Atlantic this evening and offshore tonight. A series of weak low pressure and frontal systems will pass through the area this weekend through mid week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Back edge of steadier light to moderate snowfall should push east of NYC/NJ metro and Hudson River by 8pm or so, taking until 10pm or so to push east of E LI/SE CT. Mainly light to moderate snowfall through this time period, but With 850-700mb frontogenesis band running just south of LI, and based on radar returns, some brief and localized heavy snow is likely across Suffolk County LI. Little additional accumulating snowfall expected for NYC metro and points N&W, with an additional 1 to 2 inches for CT/LI. Will likely be able to take down advisory for NYC metro/NE NJ/and Lower Hud Valley by around 8-9pm. Otherwise...divergence aloft is impressive as a 170-180 kt jet streak moves across the Middle Atlantic. Interaction/phasing of the northern and southern stream, which combined with the upper jet dynamics, will continue to organize the surface low south and east of Long Island overnight as it departs out to sea. Thermodynamic profiles do not show much liquid water saturation aloft for riming, so the snow will be a dry, high ratio type similar to what we observed Thursday morning. Ratios may be 15-18:1. Clearing and increasing winds are expected tonight behind the departing low as the pressure gradient tightens between the strengthening departing low, and strong high pressure over the SE US. Another chilly night with lows in the ranging from upper teens well inland to mid 20s at the coast.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Polar upper low pivots southeast into New England on Sat and offshore Saturday Night. WNW caa low flow over the Great Lakes, accompanied by shortwave lift and left front of 150 kt jet streak, should be enough to extend light snow shower activity into the region later Sat morning through Sat afternoon. A dusting is possible in spots, particularly NW hills. Otherwise, breezy and chilly on Sat with abundant cloud cover and glancing caa. Temps will likely hold in the lower to mid 30s for much of the region, with windchills in the 20s. Shortwave slides east Sat night, with high pressure building in from the west. This will have snow showers tapering from w to e early in the evening, with potential for good radiational cooling conds for outlying areas later Sat Night. Temps should fall into the teens for outlying areas, with mid-upper 20s for urban centers. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Models in good agreement with a fairly progressive upper pattern in place through this period, 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 will be Sunday Night into Monday as the closed low currently over Baja Mexico, shears towards the NE ahead of a developing Western US trough. Models differing in the strength of this energy and amounts of moisture drawn northward, but potential exists for a light precip event Sunday night into Monday morning. Thermal profiles suggest a start as snow or wintry mix, transitioning to rain for NYC/LI, but potentially remaining a wintry mix for the interior into Monday morning. Too early for specific details on this light precip event, but potential exists for hazardous travel conditions N&NW of NYC/LI for Monday morning commute. Thereafter, models in fairly good agreement with the broad bu shallow northern stream trough approaching the region 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 Tuesday Night. Overall, appears to be mainly a light qpf event for the Monday night into Tuesday evening period, due to limited interaction between northern and southern stream. Thermal profile suggests precip would be mainly liquid, but could be dealing with freezing rain across interior Monday night as cold air typically has a tough time scouring our 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/Thu. Upper flow flattens and even becomes a bit ridged for Thursday ahead of the next northern stream trough digging into the Upper Plains, which should allow for a moderation in temps ahead of next potential frontal system. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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Low pressure quickly passes to the east tonight as it deepens. Lingering snow and IFR conditions ends quickly this evening. Expect VFR conditions by 2-3Z, except perhaps an hour or two later eastern terminals. Expect a widespread 1-3 inches, with the highest totals across the NYC terminals into KISP, KBDR and KGON. Skies clear overnight, with increasing clouds during the day Saturday. Ceilings between 3-5 KFT expected from late morning through the afternoon. Local MVFR or IFR conditions cannot be ruled out in snow showers. Winds become westerly 5 to 10 kt this evening before increasing overnight. Occasional gusts to around 20 kt are possible overnight, otherwise speeds remain 10 to 15 kt. Westerly winds increase Saturday after 13-15Z, with speeds 15 to 20 kt and gusts 20 to 30 kt. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: VFR returns as snow ends by 1-3Z, and occasional gusts to 20 kt are possible after midnight. KLGA TAF Comments: VFR returns as snow ends by 1-3Z, and occasional gusts to 20 kt are possible after midnight. KEWR TAF Comments: VFR returns as snow ends by 1-3Z, and occasional gusts to 20 kt are possible after midnight. KTEB TAF Comments: VFR returns as snow ends by 1-3Z. KHPN TAF Comments: VFR returns as snow ends by 1-3Z. KISP TAF Comments: VFR returns as snow ends by 2-4Z. .OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY... .SAT night...VFR. .SUN...VFR during the day. Chance MVFR in a mix of -RA/-SN towards midnight. .MON...Low chance MVFR in -RA for coastal terminals, light wintry mix inland. Improvement as the day progresses. .TUE...MVFR possible with a slight chance of showers. .WED...VFR. NW winds G20-30KT
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&& .MARINE... The pressure gradient will tighten tonight as low pres passes S and E of the waters. SCA conds are expected to develop late this evening and continue through Sat, with the potential for occasional gale force gusts on mainly the ocean waters late tonight through Saturday morning. Winds and waves diminish below SCA Saturday night as high pressure builds in. Next chance for SCA conditions possibly as early as late Tuesday/Tue eve ahead of approaching cold front, but higher likelihood of widespread SCA Tuesday Night through Wednesday night with tight pressure gradient and strong caa in wake of cold front. Gales are possible during this time frame. && .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...Winter Weather Advisory until 1 AM EST Saturday for CTZ011-012. Winter Weather Advisory until 10 PM EST this evening for CTZ009-010. NY...Winter Weather Advisory until 1 AM EST Saturday for NYZ079-081. Winter Weather Advisory until 10 PM EST this evening for NYZ071>075-078-080-176>179. NJ...Winter Weather Advisory until 10 PM EST this evening for NJZ006. MARINE...Small Craft Advisory from 10 PM this evening to 7 PM EST Saturday for ANZ330-335-338-340-345. Small Craft Advisory from 10 PM this evening to 1 AM EST Sunday for ANZ350-353-355. && $$ SYNOPSIS...DS/NV NEAR TERM...DS/NV SHORT TERM...NV LONG TERM...NV AVIATION...MD MARINE...DS/NV HYDROLOGY...DS/NV EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.