Area Forecast Discussion
Issued by NWS Upton, NY

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854 FXUS61 KOKX 241336 AFDOKX Area Forecast Discussion National Weather Service New York NY 936 AM EDT Wed May 24 2017 .SYNOPSIS... A low pressure system tracks southeast of Long Island this morning with high pressure briefly building in this afternoon and evening. 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Areas of light rain falling from a mid level cloud deck will begin to dissipate in coverage the next couple of hours as low pressure passes to the south and east. 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. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... 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. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... 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. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/... Low pressure passes south of Long Island this morning. Weak high pressure briefly builds this afternoon. Another, deeper, low pressure system then approaches from the west late tonight and Thursday. VFR conditions are expected through 06z. Lingering light rain is possible at KGON through 16z. Otherwise, just middle level clouds are expected. Ceilings fall below VFR late after 06z tonight as the next low pressure system approaches. Conditions fall to IFR or less in rain towards 12Z. Light NNE-NE winds this morning become NE-ENE around 10 kt this afternoon. Winds then become Easterly late in the day into this evening. 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: Patch of MVFR will not prevail this morning with VFR expected. Winds will be NE this morning with veering to the E this afternoon. SE winds 110-140 possible this evening. KLGA TAF Comments: Amendments may be possible for changing wind direction. Winds may veer to the E this afternoon. KEWR TAF Comments: Amendments may be possible for changing wind direction. Winds may veer to the E this afternoon. 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 may veer to the E this afternoon. KHPN TAF Comments: Amendments may be possible for changing wind direction. KISP TAF Comments: Amendments may be possible for changing wind direction. Winds could veer to the ESE-SE this afternoon. .OUTLOOK FOR 12Z THURSDAY THROUGH SUNDAY... .Thursday-Friday night...MVFR, IFR possible. Slight chance of thunderstorms Thursday with E winds G20KT. .Saturday...VFR. .Sunday...MVFR/IFR developing. && .MARINE... 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. && .HYDROLOGY... 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 is possible Thursday due to antecedent wet conditions. Another round of light to moderate rainfall is possible for Sunday into Monday. && .TIDES/COASTAL FLOODING... There is an increasing threat for successive rounds of minor coastal flooding tonight through Thursday night, with the greatest threat for widespread minor and potentially moderate coastal flooding during the nighttime cycles. This is due to a slow moving low pressure system approaching 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... 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. && $$ SYNOPSIS...MD NEAR TERM...MD/DW SHORT TERM...MD LONG TERM...DW AVIATION...BC/DS MARINE...MD/DW HYDROLOGY...MD/DW TIDES/COASTAL FLOODING...

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