Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 180012 AFDOKX Area Forecast Discussion National Weather Service New York NY 712 PM EST Fri Nov 17 2017 .SYNOPSIS...
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Low pressure over the Canadian maritimes will move farther away tonight, as high pressure to the west moves across tonight into early Saturday. A warm front will lift to the north later Saturday, then a strong cold front will approach Saturday night, and sweep sweep eastward Sunday morning as strong low pressure passes to the north. A few weather disturbances are possible later next week.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Drier air was moving into the interior sections as dew points fall into the teens. Updated dew points and sky cover through this evening. Winds were slowly diminishing early this evening with the loss of heating. Fairly good radiational cooling conditions overnight should lead to a wide range of low temperatures.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/...
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Main concern will be an intensifying low moving into the Ohio Valley Sat morning, then across the lower Great Lakes Sat night and into the St. Lawrence Valley in Sunday. An associated warm front will lift north of the area daytime Sat, with some showers moving into the area from NYC north/west in the afternoon. The pressure gradient between the departing high and the approaching low will quickly tighten up, with S-SW winds gusting to 25-30 mph in most places, and as high as 35 mph across Long Island. Main impacts ahead of and following a strong cold trailing the low expected Sat night into Sunday, with S-SW winds increasing further and a band of moderate to heavy showers sweeping across with the front overnight. Models show fairly good low level mixing with max boundary layer winds from 40-55 kt, highest across eastern Long Island and SE coastal CT. Do not think the full complement of these winds will mix down to the surface, but gusts up to 35 mph are likely inland, 40-45 mph in NYC metro and along most of the coastline, and 50-55 mph across eastern Long Island. Confidence level in seeing winds over 60 mph is not quite high enough to warrant a high wind watch for eastern coastal sections, but this could change with later forecasts. Will have to watch band of moderate to heavy showers with the cold front itself for best low level momentum transfer on the western fringe of the low level jet. Winds could abate somewhat right after cold fropa, then should pick up from mid morning into the afternoon after the passage of a strong mid level vort max, via strong downward momentum transfer of W-NW 40-kt H9 winds to the surface, with gusts up to or just over 45 mph likely during this time frame.
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&& .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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A broad area of high pressure will build into the region Monday and Tuesday. This will produce fair weather. SuperBlend was used for temperatures except for Monday night, where MEX was used to better capture radiational cooling. Wednesday remains a bit of a question. A cold front will be approaching from the west. In addition, there remains the suggestion that some semblance of a coastal low will develop. The 12Z GFS is way off the Southeast coast and not a factor. The 12Z ECMWF is trending west and now produces a solid swath of rain across the area. The forecast has been trended towards the ECMWF, with low chances for precipitation included for all areas. The rain would help to suppress high temperatures as well. The cooler SuperBlend was used as a result. The cold front comes through Wednesday night. The ECMWF is much different than the GFS, which pours the cold air into the region. The ECMWF keeps the coldest air locked to the north of the area, most likely due to the dynamics of the strengthening offshore low. A blend of the models was used, however depending on how the pattern ultimately develops, Thanksgiving temperatures could end up being roughly plus or minus 5 degrees from the current forecast for highs. All solutions are dry for the day however, followed by a continuation of the dry weather on Friday. The GFS does spin up a low along the subtropical jet and tracks it east of the area on Friday. The ECMWF spins up something similar on Saturday. This feature will need to be watched for any westward trend.
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&& .AVIATION /23Z FRIDAY THROUGH WEDNESDAY/...
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High pressure slides east of the region tonight into Saturday, with a low pressure system approaching from the West. VFR through Saturday morning, with increasing potential for rain showers and MVFR or lower conds developing late Sat into Sat evening. Winds subside quickly through this evening. Southerly winds increase Saturday morning into early Saturday afternoon. SW winds 15 to 20 kt with gusts 25 to 30 kt likely for coastal terminals Saturday aft/eve. ...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: Occasional NW gusts to around 20 kt through around 02z. Diminishing winds generally right of 310 magnetic this evening. Southerly gusts to 30 kt likely for Sat evening push, with MVFR or lower conditions in -shra developing. KLGA TAF Comments: Occasional NW gusts to around 20 kt through around 02z. Diminishing winds generally right of 310 magnetic this evening. Southerly gusts to 25 kt likely for Sat evening push, with MVFR or lower conditions in -shra developing. KEWR TAF Comments: Diminishing winds generally right of 310 magnetic this evening. Southerly gusts to 20 kt possible for Sat evening push, with MVFR or lower conditions in -shra developing. KTEB TAF Comments: Diminishing winds generally right of 310 magnetic this evening. Southerly gusts to 20 kt possible for Sat evening push, with MVFR or lower conditions in -shra developing. KHPN TAF Comments: Occasional NW gusts to around 20 kt through around 02z. Southerly gusts to 20 kt possible for Sat evening push, with MVFR or lower conditions in -shra developing. KISP TAF Comments: Southerly gusts to 30 kt likely for Sat evening push. .OUTLOOK FOR 00Z SUNDAY THROUGH TUESDAY... .Saturday Night...MVFR or lower conditions in -SHRA. LLWS at night, SW flow 40-50 kt at 2 kft AGL. S-SW winds G25-35KT and occasionally higher for coastal terminals. .Sunday...Conditions gradually improve to VFR with showers ending by afternoon. NW windshift Sunday morning, with NW winds G30-40KT through the day. Gusts diminish to 25-30 kt Sunday evening. .Monday...VFR. W-NW winds G20-30KT. Gusts diminish gradually at night. .Tuesday...Mainly VFR. MVFR possible late Tuesday night with showers. SW winds G15-20KT. .Wednesday...MVFR possible with showers. W-NW winds G15-20KT.
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&& .MARINE...
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Allowed the small craft advisory to expire for the western ocean waters and seas and winds have fallen below criteria, and with marginal small craft conditions to the east will allow the advisory east of Moriches Inlet to continue until 1000 PM. A Storm Watch has been issued for the eastern ocean waters for Sat night into early Sunday morning, for frequent gusts up to 50 kt in S-SW flow ahead of an approaching strong cold front. Gale warnings have been issued elsewhere, beginning Sat afternoon on the western ocean waters, and elsewhere Sat evening, with S-SW winds increasing to 40-45 kt Sat night. W-NW gales should continue after the cold frontal passage into at least Sunday afternoon, and possibly into Sunday night especially on the ocean. SCA conds will follow into Mon, and are still possible mainly on the ocean into Tue. Conditions may improve to below advy criteria on Wed.
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&& .HYDROLOGY... A band of moderate to locally heavy showers with a strong cold frontal passage late Sat night should cause no more than local nuisance impacts. && .TIDES/COASTAL FLOODING...
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Water levels will approach minor flood thresholds with Sat morning high tide, but are expected to remain just below. Storm surge guidance for Sunday morning high tide may to be on the low side given the strength of southerly winds expected Sat night into Sunday morning ahead of a cold front. But typically, S/SW winds are not conducive to building surge. There is a low probability of a surge of 1-2 ft Sunday morning. If these surge levels developed, minor coastal impacts in a strong SW/W flow would be felt mainly across eastern portions of the Great South Bay into Moriches Bay. Elsewhere any impacts would be brief and localized.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Gale Warning from 6 PM Saturday to 6 PM EST Sunday for ANZ330- 335-338-340-345. Storm Watch from Saturday evening through Sunday morning for ANZ350-353. Gale Warning from 1 PM to 6 PM EST Saturday for ANZ350-353. Gale Warning from 1 PM Saturday to 6 PM EST Sunday for ANZ355. Small Craft Advisory until 10 PM EST this evening for ANZ350.
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&& $$ SYNOPSIS...JMC/Goodman NEAR TERM...Goodman/19 SHORT TERM...Goodman LONG TERM...JMC AVIATION...NV MARINE...JMC/Goodman/19 HYDROLOGY...JMC/Goodman TIDES/COASTAL FLOODING...NV

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