Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 080456 AFDOKX Area Forecast Discussion National Weather Service New York NY 1156 PM EST Thu Dec 7 2017 .SYNOPSIS... High pressure remains over the region through Friday. An area of low pressure continues to organize along the Mid-Atlantic Coast Friday night, then tracks to the south of Long Island on Saturday, then into the Canadian Maritime Provinces by Sunday morning. High pressure builds in from the southwest on Sunday and Monday. Another area of low pressure impacts the region on Tuesday and Wednesday, followed by high pressure for the end of the week. && .NEAR TERM /THROUGH FRIDAY/...
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High pressure remains over the region tonight and Friday. Winds have weakened over the last few hours, but should still remain mixed enough to prevent full decoupling. Clouds will also gradually increase through the night as upper jet begins to amplify aloft. Aloft, a weak shortwave passes to the north, with another shot of cold air behind it. As the main upper trough axis moves eastward, waves of low pressure develop and ride along a stalled cold front off the southeast coast during the day Friday. The air will be too dry for any precipitation, but should see abundant high and potentially middle level clouds through the day. A MAV/MET/ECS blend was used for temperatures in the near term. Temperatures remain at or slightly below normal for this time of year. Lows tonight fall into the 20s and lower 30s, while highs tomorrow climb into the 40s.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/... Focus this time frame is the potential impacts of a coastal low (or series of lows) that track to the south/southeast/then east of Long Island Saturday-Saturday night. The GFS remains a fast outlier, so has been discarded. The CMC keeps vacillating from a track well out to sea, to a storm with significant impacts on the area, the run to run inconsistencies, and that it currently is bucking model trends of a solution closer to the coast, has this model also being discarded. The SREF does not cool the low levels to saturation, so its thermal profiles in the low levels are too warm, it has been discarded for determining rain/snow lines. The forecast Friday night-Sunday is thus based primarily on a blend of the ECMWF/NAM/UKMET. A northern stream kicker diving into the southern stream portion of the deep layered trough Friday night will help to consolidate a broad area of low pressure along the southeastern coast, into a less broad and deeper area of low pressure off the Carolina coast by Saturday morning. There still remains some difference in timing of onset of sufficient isentropic lift to cause precipitation Friday night, for now have limited pops to chance over mainly SE Suffolk County. This shortwave then pushes up the Mid-Atlantic coast on Saturday, helping to further consolidate and strengthen the surface low SE of Long Island - most likely just to the SE of the 40N/70W benchmark. As a result, the best chance of precipitation will be mainly from NYC metro/SW CT on east - so have likely to categorical pops here. This low then tracks to the NE Saturday night with he supporting shortwave and a northern stream shortwave trough building into the area. This trough then lifts to the NE on Sunday. As a result gradually tapper off pops from W to E Saturday night and Sunday morning. In terms of sensible weather, expect any precipitation that falls Friday night to be 1) mainly, if not entirely after midnight 2) light 3) mainly as snow - with little if any accumulation. With increasing isentropic lift on Saturday expect coverage and intensity to increase. Wetbulb effect will bring temperatures down into the lower-mid 30s across most of the region as this happens. As a result expect a wet snow, with snow-liquid ratios around 7:1. This cooling also will change any rain/rain-snow mix over coastal areas/NYC to all snow. For now looking at accumulations of generally 1-3 inches across the Lower Hudson Valley/NE NJ/NYC (with less than an inch possible over western Orange County, and 3-6 inches over S CT/Long Island, with highest amounts over SE CT and parts of eastern Long Island. There still remains though some uncertainty in terms of the track/strength/timing of the low. If the westward trend with the system continues, there will be the potential for more mixing near the coast, limiting amounts over SE areas, and also increasing snowfall amounts farther to the west. A track farther offshore, will increase likelihood of mainly snow, but decrease amounts. For now, will highlight the threat for the possibility of reaching winter storm warning accumulations (6" or more) over S CT/Long Island. && .LONG TERM /MONDAY THROUGH THURSDAY/... High pressure briefly builds into the region Sunday night and Monday before the next amplification of the mean upper trough occurs Tuesday into Wednesday. The models continue to indicate another area of low pressure developing over or just offshore late Tuesday into Tuesday night. It is still too early at this time to get specific with precip type and amounts, but it does appear that there is another chance at snow with this system. High pressure then returns for the end of the week. Temperatures will remain below seasonable levels through the long term period. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... High pressure will build over the area on Friday. Low pressure will pass offshore on Saturday. VFR through the TAF period, although a few flurries are possible through 5Z. Westerly flow can be expected through the TAF period. Although speeds will generally be at or below 10 kt, occasional gusts to around 20 kt are possible through approximately 4-6Z. .OUTLOOK FOR 00Z SATURDAY THROUGH TUESDAY... .Friday Night...MVFR with snow possible after 6Z. .Saturday...MVFR or lower likely with snow. Accumulations possible, particularly east of the Hudson River. .Sunday...Light snow may linger in the morning, otherwise becoming mainly VFR. West winds 20-25 kt. .Monday...VFR during the day with light snow possible at night. .Tuesday...MVFR or lower is possible with snow and/or mixed precipitation. && .MARINE...
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The ocean and eastern waters small craft advisory remains in effect through 6 am Friday as gusts 25 to 30 kt are expected. The gusts should subside gradually overnight. Ocean and Eastern waters which remains up through the night. Ocean seas will also begin subsiding Friday. A relaxed pressure gradient will limit winds to 10 kt or less Friday night. The pressure gradient tightens Saturday and remains moderate into Sunday, with sustained winds up to 15-20 kt. Gusts up to 25- 30kt are possible mainly over the coastal ocean waters on Saturday night and over all waters on Sunday. A period of small craft conditions can be expected next week as a low pressure systems move across the area waters Tuesday and Wednesday.
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&& .HYDROLOGY... Around 1/4-2/3 of an inch of qpf (with lesser amounts over Orange County) is expected from late Friday into early Sunday morning. With this expected to fall mainly, if not entirely as snow, little or no hydrologic impacts are expected. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. See our headline news on the web at: http:/weather.gov/nyc && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 6 AM EST Friday for ANZ330-340-350- 353-355.
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&& $$ SYNOPSIS...BC/Maloit NEAR TERM...BC/DS SHORT TERM...Maloit LONG TERM...BC AVIATION...12 MARINE...BC/Maloit HYDROLOGY...BC/Maloit EQUIPMENT...

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