Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 211400 AFDOKX Area Forecast Discussion National Weather Service New York NY 1000 AM EDT SUN AUG 21 2016 .SYNOPSIS... A frontal system approaches from the Ohio Valley this afternoon and moves through the region tonight. High pressure then dominates the upcoming week. A cold front approaches late in the week. && .NEAR TERM /THROUGH TONIGHT/...
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Upper level ridge and embedded shortwave over the Great Lakes and into the Ohio Valley continue to move east through the day and begins to become negative this evening, then lift into New England late tonight. At the surface...a cold front associated with Canadian low pressure approaches the region late today...and then moves across the area tonight. Variable cloudiness in the warm and humid airmass remains as bands of convection stream across the eastern portions of the CWA and any remaining stratus continues to dissipate. A weak shortwave across Long Island and into coastal southern New England, and surface convergence combine to produce scattered showers. With the wave weakening and slowly moving to the northeast this morning into tonight expect the showers to gradually end. There is a moderate risk of rip currents along the Atlantic facing beaches today...with 3 ft SE wind waves and 1 to 1 1/2 ft long period se swell. Late in the day and tonight with the approach of the longwave trough...showers and thunderstorms will become more numerous and likely. Best forcing appears to lag north and west of the region as the front moves through...with late developing modest deep layer shear in a marginal instability environment. With a tropical airmass heavy rain will be likely in any of the showers and thunderstorms. The threat for any strong to severe storms appears to be quite low at this time due to late day/evening timing...weak instability...and lagging deep layer shear. With strengthening low-level shear/veering wind profile ahead of weak wave development...low lcl`s...and weak surface instability will have to monitor for shallow rotating updrafts in any tstms...particularly along the coastal plain.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... Shortwave axis slides through the Northeast on Monday. At the surface...high pressure builds in from the west. Mostly sunny outside of early sct instability cu. Otherwise...a noticeably drier airmass with near seasonable temps in the lower 80s to 85 coastal plain and upper 70s to lower 80s interior on a gusty nw flow. High pressure continues to build in Monday night with relatively cool and dry conditions. Good radiational cooling conds possible across outlying areas...with lows generally in the mid to upper 50s outside of the urban centers. Lows in the lower 50s...possibly upper 40s across rural areas. Generally lower to mid 60s nyc/nj metro. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Northern extent of southern upper ridging gradually builds into the region through midweek...flattening a bit late week into weekend. At the surface...sprawling high pressure builds in from the west through midweek...and then gradually centers itself south and east late week. Models signal a northern stream shortwave approaching and moving through northern New England Fri/Sat. An associated weak cold frontal appears to approach on Fri...but low confidence on whether it makes it through the region intact based on dominance on southern ridging. In terms of sensible weather...sunny...dry and gradually increasing warmth and humidity through the week. A late week chance of shra/tsra if front holds together. Overnight lows through midweek should be rather comfortable in the 50s and 60s...gradually rising for late week. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... A cold front approaches from the west today. Unsettled weather continues. A pop up shower is possible at any time, but coverage is expected to be sparse through the morning. Otherwise, any patchy stratus and associated MVFR ceilings should lift. Generally expect VFR conditions with broken CU, except in any heavier shower. Showers and thunderstorms become likely late in the day, approaching western terminals after 20-22z, and eastern terminals 22-00Z. These showers and storms move through during the evening hours, and should end around midnight. SE winds increase this morning with speeds of 10 to 15 kts. Cannot rule out occasional gusts in the 15 to 20 kt range. Winds begin to shift this evening as the cold front moves through, and after midnight eastern terminals. .OUTLOOK FOR 12Z MONDAY THROUGH THURSDAY... .Monday-Thursday...VFR. NW winds G15-20kt possible Monday afternoon/evening. && .MARINE...
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Winds and seas are expected to remain below small craft levels ahead of an approaching cold front, as southeasterly winds increase. There may be occasional gusts near 25 KTS this afternoon, and seas may approach 5 feet on the outer forecast waters. However, with the short duration and uncertainty will not have an advisory posted. Behind the front winds shift to NW and an occasional gust to 25 kt cannot be ruled out during the day Monday. High pressure builds in for Tuesday through Thursday with winds and seas remaining below advisory levels.
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&& .HYDROLOGY... This afternoon into tonight an average of 1/2 to 1 inch of rain is expected...with localized swaths of 1 to 2 inches possible. Minor urban flooding is the primary hydrologic threat...with a localized flash flooding threat from any training cells. Note...coupling of any heavy rainfall rates with high tide across NYC/NJ metro and LI late this evening will increase the urban flood threat in coastal areas. Dry weather is then expected for much of next week. && .TIDES/COASTAL FLOODING... Water levels will approach minor flood levels across SW CT during the afternoon high tide and western Great South Bay during the late morning and evening high tides. Se winds of 10 to 15 mph may have a few spots briefly touching minor flood levels. Note...coupling of any heavy rainfall rates with high tide across NYC/NJ metro and LI late this evening will increase the minor flood threat in coastal areas. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.