Area Forecast Discussion
Issued by NWS Upton, NY

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935 FXUS61 KOKX 300009 AFDOKX Area Forecast Discussion National Weather Service New York NY 809 PM EDT Mon May 29 2017 .SYNOPSIS... Low pressure moves well southeast of the area tonight. A weak cold front slowly approaches from the west through Tuesday then moves through late Wednesday afternoon into the evening hours. High pressure then briefly builds back for Thursday. A couple of cold fronts follow for Friday night and Saturday. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... The fcst was on track with no major changes made. The earlier vorticity maximums ahead of a broad upper low have moved offshore, ending steadier rain across the area. Subsidence aloft observed on WV imagery should act to maintain if not strengthen the low level inversion. Given the continued onshore flow trapping moisture beneath the inversion, periods of drizzle and patchy fog will likely persist through the night. Cloud cover and onshore flow will moderate temperatures overnight keeping values close to climatological normals. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Fog and drizzle will likely continue through the morning, particularly closer to the coast as onshore flow persists beneath a low-level inversion. Although the low-level cloud deck may lift some, clearing appears unlikely and as such any instability ahead of the approaching system will remain elevated. Shower chances will increase through the day from west to east ahead of a convectively enhanced vorticity maximum. Any thunderstorm chance will be greatest to the north and west of the city, but thereafter the marine influence may gradually decrease ongoing activity leading to mainly showers overnight. At the moment instability appears weak, but if a stronger cell can develop to the north and west of the city, given strengthening deep-layer wind shear, small hail will be possible. Onshore flow leads to lowering clouds and the development of occasional drizzle and patchy fog once again, outside of any steadier rain associated with the aforementioned vorticity maximum. Similar to Monday, high temperatures will be below normal while lows will be closer to climatological normals. There is a moderate risk of rip currents at Atlantic facing beaches on Tuesday. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... A cold front approaches on Wednesday and is forecast to move through the area late in the day to early evening hours. Lift ahead of the front, plus upward motion from a shortwave and possibly a coupled jet structure aloft are expected to produce scattered showers during this period. CAPES are forecast to be high enough for some thunderstorms, some of which could produce strong gusts with 0-6km shear around 50 KT. High temperatures near normal. Zonal flow aloft and weak surface ridging should keep us dry on Thursday along with high temperatures once again near normal. The timing of the next cold front is still uncertain as a closed 500mb low drifts across southern Quebec Friday into Saturday. Looks like the main cold front would pass through sometime on Saturday with a weak front or pre-frontal trough shifting through the region Friday evening. Will go with isolated to scattered showers and thunderstorms from Friday afternoon through Saturday for now. Some uncertainty in the weather pattern continues into Sunday and Monday, owing to differences among the models regarding the magnitude of upper and surface ridging to our west behind the departing upper low over the Canadian Maritimes. Prefer the drier/more ridging solution of GFS, so will go with dry conditions on Sunday. Then with an upper trough axis moving closer on Monday, isolated showers and thunderstorms with the cold pool aloft. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Weak high pressure over the area will slowly give way to a frontal system approaching from the west the next couple of days. This will keep the area under an easterly flow with low clouds, fog, and a chance of light rain or drizzle. Widespread MVFR conditions lower to IFR overnight, and then gradually improve after daybreak Tuesday. There is some uncertainty though with ceilings and visibilities overnight as some of the guidance indicates several hours of VFR conditions as the low-level ridge strengthens over the area with drier air working in at the low levels. Confidence in this scenario is low. Mainly MVFR on Wednesday with a chance of an afternoon shower or thunderstorm from NYC metro NW. E/SE winds overnight at 5 kt or less, then ramping up to 7-12 kt Tuesday afternoon. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Period of VFR conditions possible this evening. KLGA TAF Comments: Period of VFR conditions possible this evening. KEWR TAF Comments: Period of VFR conditions possible this evening. KTEB TAF Comments: Period of VFR conditions possible this evening. KHPN TAF Comments: Ceilings may occasionally be MVFR. KISP TAF Comments: Period of VFR conditions possible this evening. .OUTLOOK FOR 00Z WEDNESDAY THROUGH SATURDAY... .Tuesday night...Low clouds with IFR conditions. Chance of showers, possibly a thunderstorm. .Wednesday and Wednesday night...IFR to start, improving to VFR by afternoon. Chance of showers and possibly a thunderstorm in the afternoon/evening hours. .Thursday...VFR. .Friday and Saturday...Chance of showers and thunderstorms with MVFR or lower conds. && .MARINE... SCA in effect through this evening with seas 4 to 7 ft. Increased seas slightly above guidance to account for current trends, though seas will slowly begin to subside below SCA levels tonight. A relaxed pressure gradient over the region from Tuesday into Friday morning should keep winds over the local waters below advisory criteria. The pressure gradient then tightens, and combined wind waves and swell could build seas to 5 ft on the ocean by late in the day Friday, which could then linger through Saturday. Non-ocean waters should remain below SCA criteria during this period. && .HYDROLOGY... No significant widespread hydrologic impacts are expected through the week. && .TIDES/COASTAL FLOODING... Water levels may approach minor coastal flood benchmarks with the high tide cycle tonight, mainly for the southern bays of Nassau/NYC. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ350- 353-355. && $$ SYNOPSIS...JC/MD NEAR TERM...JMC/MD SHORT TERM...MD LONG TERM...JC AVIATION...DW MARINE...JC/MD HYDROLOGY...JC/MD TIDES/COASTAL FLOODING...

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