Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 210816 AFDOKX Area Forecast Discussion National Weather Service New York NY 416 AM EDT SUN AUG 21 2016 .SYNOPSIS...
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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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Upper level ridge axis and embedded shortwave continue to slide east this morning. Meanwhile a vigorous shortwave trough sharpening over the Great Lakes today...negatively tilts and pivots through the Northeast US tonight into Monday. At the surface...a cold front associated with Canadian low pressure approaches the region late today...and then moves across the area tonight. Considerable cloudiness today due to early morning stratus...diurnal convective cu...and then increasing high/mid clouds this afternoon ahead of approaching frontal system. Still with some breaks of sun expected in the tropical maritime airmass...temperatures should climb into the lower to mid 80s for most areas...with upper 80s across NE NJ and portions of the lower hud valley. With weak shortwave troughing aloft this morning and an increasingly moist and marginally unstable airmass...se to nw stream of iso- sct shra/tsra off ocean expected to continue this morning into early afternoon. Best coverage appears to be across Western LI/CT and westward in vicinity of washing out surface trough and with lift into hill terrain. If a pronounced sea breeze front develops today...could have to watch for localized flash flood threat in and around Nassau county...NYC/NJ metro...SW CT...Westchester in late morning/early afternoon. Late this afternoon into evening...increasing synoptic lift ahead of the pivoting shortwave/upper jet streak and tropical moisture convergence ahead of the cold front...should have numerous showers and embedded tstms approaching western portion of the Tri-state. This activity should then translate east across the region tonight. 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. Main convective threat appears to be torrential downpours with any convection in moist tropical environment. The threat for 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. If instability can build, cant rule out a storm or two with strong wind gusts for areas mainly west of the Hudson late day/early eve. 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. Cold front moves across the region tonight with shra/tsra pushing offshore after midnight. Partial clearing expected late tonight with drier low/mid level nw flow in wake of cold front. There is a moderate risk of rip currents along the Atlantic facing beaches today.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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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.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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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.
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&& .AVIATION /08Z SUNDAY THROUGH THURSDAY/...
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A cold front approaches from the west today. Unsettled weather continues. A pop up shower is possible at any time, but coverage will be sparse through the morning. Otherwise, patchy stratus is expected, with MVFR ceilings possible from time to time this morning. Highest probabilities for sub VFR remain across CT terminals. After any morning stratus, generally VFR conditions expected through the day today, except in any heavier shower. Showers and thunderstorms become likely late in the day, approaching western terminals after 19-20z, and eastern terminals 20-23Z. These showers and storms move through during the evening hours, and should end around midnight. Light E/SE winds early this morning become SE and increase after 14-15z. Speeds of 10 to 15 kts are expected, and cannot rule out occasional gusts in the 15 to 20 kt range. Winds begin to shift this evening as the cold front moves through, except well east. .OUTLOOK FOR 06Z MONDAY THROUGH THURSDAY... .Late tonight...Becoming VFR from W to E as showers end. Winds shift to the NW. .Monday-Thursday...VFR. NW winds g15-20kt possible Monday afternoon/evening.
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&& .MARINE...
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Southeast winds continue today ahead of a cold front. Wind speeds increase to 10 to 20 kt. Winds shift around to the NW behind the cold front late tonight and through the day Monday. Gusts up to 20 kt are expected, and an occasional gust to 25 kt cannot be ruled out during the day Monday. However, no headlines are planned across the area waters. As high pressure builds Tuesday-Thursday, winds lighten and become southerly once again. Seas build somewhat late today, and tonight ahead of and behind a cold front. Ocean seas should remain below 5 ft through Monday, and certainly Tuesday through Thursday with high pressure in control.
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&& .HYDROLOGY...
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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 this evening would increase the urban flood threat in coastal areas. Dry weather is then expected for much of next week.
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&& .TIDES/COASTAL FLOODING...
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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.
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&& .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...NV NEAR TERM...NV SHORT TERM...NV LONG TERM...NV AVIATION...PW MARINE...PW HYDROLOGY...NV TIDES/COASTAL FLOODING...

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