Area Forecast Discussion
Issued by NWS Upton, NY

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309 FXUS61 KOKX 301334 AFDOKX Area Forecast Discussion National Weather Service New York NY 934 AM EDT SAT JUL 30 2016 .SYNOPSIS... High pressure moves off the New England coast today as low pressure slowly approaches from the Ohio Valley. This low tracks along a frontal boundary to the south into early next week. An upper level disturbance passes through on Tuesday with high pressure then returning through Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... A mid deck is moving across the Lower Hudson Valley with some weak returns on radar. There has been a downward trend with these echoes over the last hour as there is still some subsidence to overcome with weak ridging aloft and surface high over the area. Also noting some drier air advecting southward under a light northerly flow over the interior where dew points have fallen into the lower 60s. Have adjusted PoPs to account for the latest trends, but otherwise the forecast remains on track. As the weak ridge aloft flattens today, a broad trough east of the Rockies tracks slowly eastward. Clouds will gradually increase as warm advection ensues and surface low pressure slowly approaches from the Ohio Valley. Still appears as though the best coverage of showers and thunderstorms will be from the city north and west this afternoon. This is where the best instability and lift will reside. As the activity translates eastward, there should be a downward trend in intensity as the precipitation encounters the surface high just to the east. Highs will be in the lower to middle 80s. && .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/... As deep layered ridging strengthens across the plains and SW US and a cutoff low pressure system tracks across western Canada...the downstream H5 flow will amplify. Unsettled weather continues through into early next week as the amplifying upper level trough approaches. However...the shortwave and LFQ of jet stream are progged to lift through western New York State late tonight and Sunday. Divergence aloft will pass through western portions of the local area Sun aftn with additional showers and tstms expected. With abundant moisture still present through the column...some storms could produce heavy rainfall. Sfc low pres approaching from the west slowly passes S of Long Island Sunday night through Monday night...followed by the upper trough axis on Tue. Sct showers/tstms remain a possibility with locally heavy rainfall. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Drier weather builds into the area Tuesday through Friday. A few isolated showers will be possible on Tuesday right behind the upper trough. Temperatures remain at or slightly below normal through Tuesday. Then, an increase in heat and humidity start to return. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... High pressure builds offshore the New England coast today with low pressure approaching form the Ohio Valley. Mainly VFR conditions with increasing mid clouds. Patches of stratus/fog across LI and CT terminals should mix out within the next hour. Showers are likely this afternoon, mainly west of NYC, then becoming more widespread late tonight. Isolated thunderstorms possible. Light N/NE winds this morning, becoming S/SE by afternoon at 5 to 10 KT. Winds back to the more E/SE tonight as the low approaches from the west. .OUTLOOK FOR 12Z SUNDAY THROUGH WEDNESDAY... .Sunday-Monday Night...Chance of showers and possibly a tstm. MVFR or lower conditions possible. .Tuesday-Wednesday...Mainly VFR, although isolated showers possible. && .MARINE... A frontal boundary will remain south of the waters through early next week until low pressure passes to the east Monday night into early Tuesday. This will result in a mainly E/SE flow which will be strongest Sunday afternoon/evening, with possible gusts up to 20 kt on the ocean waters. High pressure will then follow for the mid week. Sub-sca conditions are forecast during the period. && .HYDROLOGY... A large range of rainfall is expected across the area this weekend. Average QPF from this afternoon through Sunday evening is expected to be from around 1/3 of and inch to 1 inch east of NYC and 1 to 1 3/4 inches N and W of NYC. Locally higher amounts are possible in any heavier showers. Minor urban flooding would be the main hydrologic impact in any heavier shower/thunderstorm. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...24 NEAR TERM...24/DS SHORT TERM...24 LONG TERM...24 AVIATION...DW MARINE...DW HYDROLOGY...24

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