Area Forecast Discussion
Issued by NWS Upton, NY

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575 FXUS61 KOKX 270820 AFDOKX Area Forecast Discussion National Weather Service New York NY 420 AM EDT Sat May 27 2017 .SYNOPSIS...
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Multiple weak waves of low pressure pass to the south through Monday, as high pressure gradually builds down from southeastern Canada. This high retreats to the northeast Monday night. A series of weak fronts or troughs of low pressure cross the area Tuesday through Thursday. Weak high pressure then builds in through Friday, as a front stalls to the south of Long Island.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Hi-res models indicate that a convective complex currently over ohio passes just to the SW/S of the area this afternoon (consistent with trajectory of mean 850-500 hPa flow). Do have slight chance pops over the SW 1/5 of the CWA late this afternoon in case convection strays a bit farther to the NE than currently progged, but would not be surprised if entire area stayed dry today as northern stream shortwave ridging builds to the north. Highs today should be near normal, with some sun expected this afternoon, leaned towards warm edge of guidance.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
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Northern stream 850-500 hPa ridging builds in tonight, as onshore flow sets up below 900 hPa. Could end up seeing some patchy drizzle late tonight/into early Sunday morning as a result. Lows tonight should be a few degrees above normal. The aforementioned ridge axis transits over the area Sunday, with moisture trapped under the subsidence inversion making for a mostly cloudy day. Given expected cloud cover and onshore flow, did cut back on highs to around 5-10 degrees below normal. this was based on blending NAM/ECWMF 2-meter temperatures in with MET/ECS guidance and a mix down from 975-925 hPa per BUFKIT soundings.
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&& .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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The northern stream ridge slides offshore Sunday night, allowing for light rain to overspread most of the area with some modest isentropic ascent (could remain dry over far eastern portions). A northern stream shortwave rotates across the area around the base of a closed low over Ontario/Northern Great Lakes Monday. Even with onshore flow, Showalter Indices are progged down to -2 to -4 by afternoon in response to fairly steep mid-upper level lapse rates, have opted for showers, with a chance of thunderstorms by afternoon. Given Showalter Indices cannot rule out some locally strong storms and cannot 100% rule out a severe cell or two. The main threat would be large hail - with wet bulb zero heights progged at 8-9 thousand feet late Monday afternoon/early Monday evening. The marine inversion likely will prevent any gusts to severe levels. The showers with embedded thunderstorms should come to an end from SW to NE Monday night as the shortwave trough exits to the NE. The closed upper low and longwave trough will be slow to move east through the middle to late part of next week as a series of shortwaves rotate through the trough, while at the surface weak lows, or troughs move through the area. There remains a lot of uncertainty with the timing and placement of the systems through the upcoming week. As a result, there could be a prolonged period of unsettled weather. Will carry slight chance to low chance probabilities through Thursday, highest over northern zones, closest to the closed low/any shortwaves rotating around it. For now have gone with a dry forecast Thursday night and Friday as the main axis of the opening closed low is progged to lift to the northeast.
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&& .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
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Mainly VFR through the TAF period, but there could be a brief period of 030-035 cigs from about 15Z-18Z give or take an hour today. There will also be a slight chance of showers for the NYC metro terminals from about 20Z-23Z as a weakening disturbance passes just south. NW winds will diminish into this morning. Sea breezes should develop along the coast this afternoon, reaching KLGA/KEWR/KTEB/KHPN late this afternoon, after about 20Z. Some guidance is indicating potential for an ENE rather than S breeze to develop at KLGA, so will have to watch for this potential. .OUTLOOK FOR 06Z SUNDAY THROUGH WEDNESDAY... .Late tonight...MVFR cigs developing with some patchy drizzle. Chance of IFR cigs toward daybreak at KHPN/KISP. .Sunday...MVFR and any local IFR cigs gradually improving to VFR by afternoon. .Sunday night...VFR, but with chance of light rain late. .Monday...MVFR conds likely and IFR conds possible. Showers likely and chance of tstms. .Monday night...Conds improving to VFR by late evening. .Tuesday-Wednesday...Mainly VFR. Chance of showers/tstms mainly NW of the NYC metro terminals.
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&& .MARINE...
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Southerly swells have diminished a little more quickly than expected, with 5 ft only at buoy 44017. Therefore the SCA for Hazardous Seas will continue on the ocean E of Moriches Inlet until 8 AM, and has been cancelled farther west. SE winds increasing to 15-20 kt on Mon could lead to ocean seas reaching 5 ft again Mon afternoon/evening. Otherwise, outside of any tstms on Monday, winds/seas on the waters should remain tranquil.
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&& .HYDROLOGY...
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No significant widespread hydrologic impacts are expected through at least the middle of next week.
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&& .TIDES/COASTAL FLOODING...
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The combination of high astronomical tides and southerly swell will keep water levels within striking distance of minor coastal flood benchmarks for several high tide cycles into early next week. A coastal flood advisory is in effect for the high tide cycle tonight for the south shore bays of Brooklyn/Queens/Nassau, also for the shores of Westchester/Fairfield along western Long Island Sound.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...Coastal Flood Advisory from midnight tonight to 3 AM EDT Sunday for CTZ009. NY...Coastal Flood Advisory from midnight tonight to 3 AM EDT Sunday for NYZ071. Coastal Flood Advisory from 9 PM this evening to 2 AM EDT Sunday for NYZ075-178-179. NJ...None. MARINE...Small Craft Advisory for hazardous seas until 8 AM EDT this morning for ANZ350.
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&& $$ SYNOPSIS...Maloit NEAR TERM...Maloit SHORT TERM...Maloit LONG TERM...Maloit/MET AVIATION...Goodman MARINE...Goodman/MET HYDROLOGY...Maloit/MET TIDES/COASTAL FLOODING...Goodman

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