Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 240825 AFDOKX Area Forecast Discussion National Weather Service New York NY 425 AM EDT Wed May 24 2017 .SYNOPSIS...
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A low pressure system tracks southeast of Long Island today followed by weak and brief high pressure building in tonight. A slow moving low pressure system affects the area Thursday into Friday before weak high pressure returns again for Saturday. Another frontal system will then impact the area for the latter half of the holiday weekend.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Rain is just beginning along the coast on the northern fringe of a deepening coastal low that will largely pass to the southeast of the area. The best chance of any rainfall will be this morning before the parent short wave and attendant surface low moves northeast of the area by afternoon. With a broad upper low to the west, expect cloudy conditions to continue through the afternoon despite precipitation ending from west to east. In combination with cloud cover, an onshore component towards the coast will keep temperatures a few degrees below climatological normals.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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Continued cloud cover ahead of the broad upper low to the west will keep temperatures overnight closer to normal. Rainfall will increase from southwest to northeast by morning as the upper low and a slowly deepening surface low move into the area. An extended period of southwest flow will continue to advect Gulf moisture northward, leading to possibly moderate rain at times through the day. As the warm front lifts through the area by afternoon, elevated instability may support a slight chance of thunderstorms, though no severe weather is expected at this time. As the surface low deepens, the tightening pressure gradient will lead to strengthening onshore flow, which will keep temperatures well below normal and also lead to coastal impacts with above normal tides. See TIDES/COASTAL FLOODING for associated impacts.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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An unsettled weather pattern continues through this period as an upper low lifts out of the Northeast on Friday, while another another drops into the Midwest and Great Lakes states over the weekend. Upper level ridging between the two systems briefly builds across the area for the first half of the weekend. Models are in good overall agreement in taking surface low pressure over the Mid Atlantic states Thursday night south and east of the area and then into the Gulf of Maine on Friday. Showers and isolated thunderstorms Thursday night will taper off on Friday with lingering clouds and showers through much of the day as deep-layered cyclonic flow remains across the region behind the departing low. Conditions will then briefly dry out Friday night into Saturday as both ridging aloft and at the surface translates east across the area. Things get a little more tricky heading in Sunday as another frontal system approaches the area. There are differences amongst the global models, in particular with the ECMWF and GGEM, as both more aggressive with a frontal wave ejecting east out ahead of the main frontal system. However, the 00Z ECMWF has trended toward the GFS, with a late day warm frontal passage on Sunday, followed by a weak cold frontal passage late Monday. There remains some uncertainty with the timing of warm advection rainfall Sunday into Sunday night. It could possibly hold off until late in the day. Scattered convection is then forecast for Memorial Day along and ahead of the cold front. Conditions briefly dry out Monday night into Tuesday before the upper trough and another cold front approach Tuesday night. Temperatures during the period will be near seasonable levels.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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A wave of low pressure will move south of Long Island Wednesday morning, and then slide east during the afternoon. Weak high pressure builds in once again behind the low Wednesday afternoon. This high weakens Wednesday evening as another, deeper, low approaches from the west. VFR conditions are expected through much of the forecast period. There is a low chance of MVFR ceilings and visibilities developing briefly toward 12Z along the coast, then improving as the rain ends from west to east. MVFR conditions are expected at KISP after 07Z and MVFR conditions will be possible at KGON. Ceilings fall below VFR late in the 30 hour TAF sites as the next low pressure system approaches. Light and variable winds become NE less than 10 KT after 06Z, then increasing to around 10 KT with gusts up to 20 KT possible Wednesday morning. Winds will become E late in the day as the next low approaches. There may be a brief period of light northerly winds 17Z to 20Z. ...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: Amendments may be possible for changing wind direction. Winds could become more northerly than forecast. low chance of MVFR cigs this morning in rain. KLGA TAF Comments: Amendments may be possible for changing wind direction. Winds could become more northerly than forecast. KEWR TAF Comments: Amendments may be possible for changing wind direction. Winds could become more northerly than forecast. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Amendments may be possible for changing wind direction. Winds could become more northerly than forecast. KHPN TAF Comments: Amendments may be possible for changing wind direction. Winds could become more northerly than forecast. KISP TAF Comments: Amendments may be possible for changing wind direction. Winds could become more northerly than forecast. low chance of MVFR cigs this morning in rain. .OUTLOOK FOR 06Z THURSDAY THROUGH SUNDAY... .Wednesday night-Friday night...MVFR, IFR possible. Slight chance of thunderstorms Thursday with E winds G20KT. .Saturday...VFR. .Sunday...MVFR/IFR developing.
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&& .MARINE...
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An initially weak pressure gradient will tighten through the day as an area of low pressure moves up the coast. As such, marginal NW SCA winds and seas will develop. Despite the departure of the initial surface low, a second area of developing low pressure to the southwest will maintain an easterly flow and allow seas to remain elevated on the ocean through Thursday. Low pressure passes off the New England coast Friday. Ocean seas of 5 to 7 ft remain through Friday, then diminish to less than 5 ft for Saturday and the remainder of the weekend.
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&& .HYDROLOGY...
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0.50" to 1.50" of rain is currently forecast from today through the day on Friday. Higher amounts are possible in any thunderstorms that develop on Thursday. Minor urban and small stream flooding given antecedent wet conditions. Another round of light to moderate rainfall is possible for Sunday into Monday.
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&& .TIDES/COASTAL FLOODING... Increasing threat for successive rounds of minor coastal flooding for the Wed Night, Thu Morning and Thu Night high tide cycles. Greatest threat for widespread minor and potentially moderate coastal flooding appears to be with the Thursday eve/night high tide cycle as a slow moving low pressure system approaches the region...and with less than 1/2 ft of surge needed in many places to reach minor flood thresholds and 1 to 2 ft for moderate. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for NYZ075-178-179. NJ...None. MARINE...Small Craft Advisory until 6 PM EDT Thursday for ANZ350-353- 355.
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&& $$ SYNOPSIS...MD NEAR TERM...MD SHORT TERM...MD LONG TERM...DW AVIATION...BC MARINE...MD/DW HYDROLOGY...MD/DW TIDES/COASTAL FLOODING...

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