Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 072230 AFDOKX Area Forecast Discussion National Weather Service New York NY 530 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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Minor updates this evening to add snow flurries to Orange County. A subtle short wave aloft and weak surface trough have resulted in enough low level instability and moisture to trigger some flurries/snow farther west. Drier conditions exist east of the mountains in PA, so expect some evaporation to occur with no accumulations anticipated. Weak surface high pressure will remain over the region tonight and Friday. Aloft, a weak shortwave passes to the north early tonight, 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. At this time, it looks like any precipitation remains to our south through the day Friday as atmosphere remains rather dry in the lower and mid levels. Therefore, will go with a dry forecast through this time. 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 /00Z FRIDAY THROUGH TUESDAY/... High pressure will be centered to our SW through tonight, meanwhile a wave of low pressure will track NE along a stalled offshore front on Saturday. VFR. W winds 10-20 kt with gusts to 25 kt into early evening. Occasional gusts to 30 kt. Gusts likely to continue through evening push for NYC/NJ terminals, gradually subside tonight. Westerly flow of 5-10 kts is expected for Friday, beginning to back to SW friday afternoon. 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: Timing of gusts ending could vary 1-2 hours from TAF. Peak gusts to 30 kt into this evening. KLGA TAF Comments: Timing of gusts ending could vary 1-2 hours from TAF. Peak gusts to 30 kt into this evening. KEWR TAF Comments: Timing of gusts ending could vary 1-2 hours from TAF. Peak gusts to 30 kt into this evening. KTEB TAF Comments: Timing of gusts ending could vary 1-2 hours from TAF. KHPN TAF Comments: Timing of gusts ending could vary 1-2 hours from TAF. KISP TAF Comments: Timing of gusts ending could vary 1-2 hours from TAF. .OUTLOOK FOR 18Z FRIDAY THROUGH MONDAY... .FRI AFT-SAT...MVFR/IFR in -SN development possible late Friday Night into Saturday Morning. Increasing likelihood for IFR or lower in -SN Saturday afternoon into Saturday Evening for coastal terminals. Improving conditions with snow tapering after midnight Sat Night. .SUN...VFR, except MVFR in isolated -SHSN Sun aft and Sun night. W/NW gusts 20-25 kt Sun/Sun Night. .MON...VFR. W/NW Gusts diminishing. .MON NIGHT-TUE...Potential for MVFR or lower in RA/SN. && .MARINE... A strengthening low level jet will result in an increase in westerly winds this evening into tonight. Expect gusts up to 30 kt. Winds then diminish late tonight and into Friday as the pressure gradient relaxes. Small Craft Advisories remain up for all the area waters through 06z, Except the Ocean and Eastern waters which remains up through the night. Seas build tonight before 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. && .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... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 1 AM EST Friday for ANZ335-338-345. Small Craft Advisory until 6 AM EST Friday for ANZ330-340-350- 353-355. && $$ SYNOPSIS...BC/Maloit NEAR TERM...BC/MD SHORT TERM...Maloit LONG TERM...BC AVIATION...NV MARINE...BC/Maloit HYDROLOGY...BC/Maloit EQUIPMENT...

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