Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 160258 AFDOKX Area Forecast Discussion National Weather Service New York NY 958 PM EST Mon Jan 15 2018 .SYNOPSIS... High pressure to the north of the area will weaken and shift eastward through Tuesday ahead of low pressure approaching from the west and a developing coastal low. The coastal low will move up the coast into the Canadian Maritimes through Wednesday night. High pressure will then build to the south through Friday, moving into the western Atlantic this weekend. Low pressure will then approach from the west early next week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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Forecast is generally on track. Sky forecast is tough overnight with the western edge of the stratocu deck across LI and CT eroding while another area of strato cu over NJ and eastern PA is encroaching on NYC. With cooling and a continued onshore flow in the low levels, expect clouds to fill back in across the entire area. Otherwise, weak warm advection just above the surface has led to the development of a stratocu deck across most of the forecast area, with enough lift as a jet streak approaches for some light flurries across portions of Connecticut and Long Island. Otherwise, generally dry conditions prevail as high pressure to the north continues a dry northeasterly flow. Low temperatures are expected to be in the teens to mid 20s, generally at or slightly below climatological normals.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/... By morning with the high pressure gradually shifting offshore, a light return flow will allow warm/moist advection to develop along the coast, increasing into the afternoon as a coastal low approaches. Meanwhile farther west, a weak clipper will approach leading to the development of initially light snow across the interior, where a winter weather advisory is now in effect. Precipitation will spread from west to east through the day, and given warming temperatures along the coast, a rain/snow mix and/or rain can be expected. Highest confidence of snow is north and west of the NYC area, while the potential for mixed p-types reduces confidence for the city into Long Island and coastal Connecticut. With the latest guidance shifting westward with the low, potential exists for a warmer solution, and therefore lower totals for the city into coastal areas. The heaviest precipitation will develop Tuesday night into Wednesday morning, as one jet streak aloft departs and another approaches, allowing the surface low to deepen as it moves up the coast. As the low departs, a return to northwest flow and cold air advection will allow temperatures to fall once again, with more snow possible. Precipitation will then taper off from west to east by evening. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... On the heels of an upper trough passing offshore early Thursday, a progressive southern branch of the polar jet becomes dominant across the lower 48. Global models are in good overall agreement with this pattern. This will result in a gradual warmup as the airmass transitions to Pacific origin. Daytime highs on Thursday will be near freezing, rising to around 50 by next Monday. Conditions will be mainly dry as a large area of high pressure over the Lower Mississippi Valley translates slowly east and passes to the south through the week and offshore this weekend. A southern branch storm system then approaches late in the weekend into early next week with a surface low forecast to track up into the Great Lakes. The trailing cold front moves through Monday night. This is likely to be a rain event with a deep layered southerly flow preceding the system. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/...
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High pressure to the north of the area will weaken and shift eastward through Tuesday ahead of low pressure approaching from the west and a developing coastal low. NE winds 5 to 10 kt will lighten and become light and variable away from the city. Winds remain light out of the ENE-E Tuesday morning, then shift to the E/SE in the afternoon. Patchy stratus is observed across the area, making for a tough ceiling forecast. In general, would expect stratus to redevelop and become more widespread toward morning, with MVFR ceilings anticipated Tuesday morning and afternoon. There is a chance of flurries or light snow Tuesday afternoon, but no visibility restrictions are expected at this time until 22-00Z. .OUTLOOK FOR 00Z WEDNESDAY THROUGH SATURDAY... .Tuesday night-Wednesday...MVFR falling to IFR in light snow into Wednesday. Rain/snow mix possible near the coast. VFR possible late. .Wednesday night-Thursday...VFR. N-NW winds G20KT. .Friday-Saturday...VFR.
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&& .MARINE...
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Ocean seas will be at least marginal SCA levels into Tuesday night in developing onshore flow. Flow returns to a northwesterly direction and begins to gust late on Wednesday, continuing into Thursday night. Small craft wind gusts and marginal seas will be likely on the ocean waters through Thursday night with a chance of small craft gusts across eastern Long Island Sound and the eastern Long Island bays. Friday through the weekend winds and seas will be below SCA levels as high pressure builds to the south and a weaker pressure gradient resides across the forecast waters.
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&& .HYDROLOGY... No significant 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. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Winter Weather Advisory from 10 AM Tuesday to 1 PM EST Wednesday for NYZ067>070. NJ...Winter Weather Advisory from 10 AM Tuesday to 1 PM EST Wednesday for NJZ002-004-103-105-107. MARINE...Small Craft Advisory until 6 PM EST Tuesday for ANZ350-353-355. && $$

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