Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 212003 AFDOKX Area Forecast Discussion National Weather Service New York NY 403 PM EDT Sun May 21 2017 .SYNOPSIS...
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High pressure moves east of the area today. A series of low pressure systems will impact the area through the week, resulting in periods of unsettled weather.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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As a high amplitude ridge moves east off the coast, mainly mid and high level clouds will advect east as warm air advection develops. The first chc of light rain will develop aft 06z from west to east with the approach of the upstream warm front. With a very dry atmosphere in place, dew pt. depressions of more than 30 degs, it will take time to moisten the sub cloud layer later tonight. Overnight lows of 45-55 degs are fcst, slightly lower than normal based on southeast winds off the cool Atlantic Ocean.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY/...
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Monday...Prepare for a widespread moderate rainfall ranging from around 2/3-inch to 1 and 1/4-inches, mainly between 8 am and pm. Minor urban flooding of low lying poor drainage areas is possible. The combination of increasing low lvl warm air advection and convergence, an upper lvl short wave mvg NE toward the area and a developing occluded front approaching will cause this rainfall along with areas of fog. As southeast winds continue blowing off the cool Atlantic Ocean, day time temperatures will range 60-65 degrees. Monday Night...Light rain will gradually end as the low moves SE of Long Island. Tuesday...As the upper lvl low digs SE across the Western Great Lakes, another short wave will rotate arnd the base of this low, causing cyclogenesis in the SE that will move NE toward the region, bringing our next chc of rain.
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&& .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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The developing upper trough over the central U.S. will continue to amplify over the midwest and southern plains Tuesday night, then move slowly east through the end of the work week. This will result in unsettled weather through the period as a series of lows and upper level vorts move through, bringing multiple chances for rain to the region. Models are in somewhat better agreement in the large scale trough evolution, although differences continue in the timing and placement of individual shortwaves and the associated sensible weather. Based on the 12Z model suite, the general consensus is for a period of rain Tuesday night into Wednesday, then again on Thursday, with a chance of lingering showers in between. The trough begins to lift to the northeast late in the week as a ridge builds in for the weekend. This will allow for generally dry conditions for a period Friday into Saturday. Models then diverge on the placement of a shortwave undercutting the ridge, which could bring a chance of rain back to the region on Sunday. Daytime highs will be near normal through the majority of the period, before rising to a few degrees above normal by the weekend. Overnight lows will run around 5 degrees above normal through the weekend.
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&& .AVIATION /20Z SUNDAY THROUGH FRIDAY/...
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High pressure moves offshore today as a frontal system approaches from the west. VFR through at least 06z tonight. S-SE winds 8-15 kt this afternoon. Winds gradually diminish overnight, and remain from the SE. Some gusts may be possible through 23Z, however they may be more occasional than frequent. Clouds lower and thicken this evening and overnight...but rain and MVFR conditions look to hold off until around daybreak. IFR conditions expected to develop after 12z. There may be some embedded thunder with the rain on Monday. Confidence on timing and placement is too low to include in the TAFs at this time. .OUTLOOK FOR 18Z MONDAY THROUGH FRIDAY... .MONDAY Afternoon...IFR in rain. Slight chance of thunderstorms. .MONDAY NIGHT-TUESDAY...Cold frontal passage around midnight Monday night at the metros. Becoming VFR Tue morning. .WEDNESDAY-FRIDAY...Chance of MVFR or lower in showers. Slight chance of thunderstorms Wednesday night into Thursday.
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&& .MARINE...
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Sub-advsy conds will remain across the waters through tonight as high pressure gradually slides off the New England coast. SE winds will increase to 15-20 kt as seas build to around 4 ft during the day Monday across the Atlantic Ocean coastal waters. Areas of fog are forecast to restrict VSBY to 1-3NM area wide through Monday evening. While winds will generally remain below SCA conditions, seas will begin to increase on Wednesday as a series of lows move over the area. SCA conditions are possible on the ocean waters Wednesday- Friday before seas begin to subside on Saturday.
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&& .HYDROLOGY...
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A widespread moderate rainfall ranging from around 2/3-inch to 1 and 1/4-inches, mainly between 8 am and pm. Minor urban flooding of low lying poor drainage areas is possible. Several opportunities exist for widespread rainfall during the mid- to late-week time period. Around one inch of additional rainfall is possible during this time period, although considerable uncertainty exists in the details of these events.
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&& .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...FEB/GC NEAR TERM...GC SHORT TERM...GC LONG TERM...FEB AVIATION...BC MARINE...FEB/GC HYDROLOGY...FEB/GC

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