Area Forecast Discussion
Issued by NWS Upton, NY

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991 FXUS61 KOKX 152123 AFDOKX Area Forecast Discussion National Weather Service New York NY 423 PM EST Fri Dec 15 2017 .SYNOPSIS...
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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.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Snow continues to overspread the Tri-State area. Impacts to the evening commute are anticipated, with potential for significant impacts within the winter weather advisory area. No changes were made to the headlines. The only change made to the snowfall forecast was across southern/coastal Long Island where some locations could approach 4 inches. This is due to increasing potential for moderate snow banding in conjunction with best frontogenesis this evening. There is a bit of uncertainty in how much snow will fall across NE NJ and interior of the Lower Hudson Valley and southern Connecticut. It is possible amounts could end up lower with minimal impact since best lift appears to be setting up just south, within the advisory area. Divergence aloft is impressive as a 170-180 kt jet streak moves across the Middle Atlantic. Our region will be located in the favored left exit region for synoptic lift this evening. There will also be interaction/phasing of the northern and southern stream, which combined with the upper jet dynamics, will continue to organize a surface low off the Middle Atlantic coast this evening and then south and east of Long Island overnight. Mesoscale models continue to indicate a swath of strong 850-700 mb frontogenesis across the southern portion of the area. The lift coincides within the dendritic growth zone which may enhance snowfall and produce banding, especially across Long Island. 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. Surface temperatures will fall into the middle and upper 20s as the snow begins continues to fall. The snow tapers off around 7-9pm in NYC and around midnight on the east end of Long Island. Liquid equivalent amounts around 0.05 inches inland and close to 0.20 inches are forecast across Long Island. 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/...
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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.
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&& .LONG TERM /SUNDAY THROUGH FRIDAY/...
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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.
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&& .AVIATION /21Z FRIDAY THROUGH WEDNESDAY/...
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***SNOW EXPECTED FOR EVENING PUSH*** Low pressure passes to the south this evening before quickly ejecting eastward overnight. Snow is already overspreading the area, and although initial conditions are VFR, expect visibilities to quickly drop as snow intensifies. Steadier snow will generally fall from around 20Z, then quickly end from west to east between 02-05Z. Expect a widespread 1-4 inches, with the highest totals across the NYC terminals into KISP, KBDR and KGON. Light and variable winds become westerly at 5-10 kt this evening. Winds increase tonight with some gusts to 20kt after midnight. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Best chance of steady snowfall with reduced visibilities expected between 20z-02z with 2-3 inches of accumulation. KLGA TAF Comments: Best chance of steady snowfall with reduced visibilities expected between 20z-02z with 2-3 inches of accumulation. KEWR TAF Comments: Best chance of steady snowfall with reduced visibilities expected between 20z-02z with 2-3 inches of accumulation. KTEB TAF Comments: Best chance of steady snowfall with reduced visibilities expected between 20z-02z with 2-3 inches of accumulation. KHPN TAF Comments: Best chance of steady snowfall with reduced visibilities expected between 20z-02z with 1-2 inches of accumulation. KISP TAF Comments: Best chance of steady snowfall with reduced visibilities expected between 20z-02z with 2-4 inches of accumulation. .OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY... .SAT...VFR. Chance MVFR after 18Z with isold -SHSN. WNW winds G20-30KT daytime. .SUN...VFR during the day. Chance MVFR in -RA/-SN towards midnight. .MON...Low chance MVFR in -RA for coastal terminals, light wintry mix inland. .TUE...MVFR possible. Slight chance of light -RA. .WED...VFR. NW winds G20-30KT
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&& .MARINE...
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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.
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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...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.
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&& $$ SYNOPSIS...DS/NV NEAR TERM...DS SHORT TERM...NV LONG TERM...NV AVIATION...MD MARINE...DS/NV HYDROLOGY...DS/NV EQUIPMENT...

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