Area Forecast Discussion
Issued by NWS Upton, NY

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376 FXUS61 KOKX 210550 AFDOKX Area Forecast Discussion National Weather Service New York NY 150 AM EDT THU JUL 21 2016 .SYNOPSIS... An area of high pressure which extends east from the Ohio Valley to off the Mid Atlantic Coast will slowly work offshore through Thursday night. A cold front approaches the region on Friday and moves through late at night into Saturday morning. High pressure then follows Saturday afternoon through Sunday. Another cold front approaches on Monday and passes through Monday night. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... A departing upper trough will continue to work offshore into the western Atlantic as anomalously warm heights associated with a ridge over the mid section of the country expand east. This will result in increasingly warmer and more humid conditions through the end of the week. At the surface, a large area of high pressure, extending from the Ohio Valley to off the Mid Atlantic coast, will slowly work east. This will keep the area dry with a weak return SW flow and nearly seasonable lows. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... Heights will continue to build aloft as the upper ridge over the mid section of the country expands east. Airmass will remain capped with no convection forecast. It will be several degrees warmer than Wednesday as a westerly flow aloft transports warmer air from the upper Midwest and Great Lakes into the region. An increase in humidity will also become more noticeable Thursday night as dew points climb through the 60s due to a strengthening SW flow. Gradient wind tightens due to the offshore high and an approaching frontal system over the upper Great Lakes. Gusts up to 20 mph are possible across the NYC metro and LI Thursday afternoon/early evening, but of a lesser magnitude to the north. Highs on Thursday will range from the lower 80s along the coast, to around 90 in the interior. Lows Thursday night will range from the mid 60s inland, to the lower 70s along the coast. These readings are about 3 to 5 degrees above normal. There is a moderate risk for rip current development at ocean beaches Thursday afternoon into evening due to the combination of 2 ft long period se swell and increasing southerly wind waves. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... A cold front approaches on Friday and passes through late at night into early Saturday morning. With increasing CAPE and a shortwave contributing to shear, particularly across the NE portion of the CWA, showers and thunderstorms, some possibly strong to severe will be possible. Best chances of this will be in the afternoon and evening hours. By Saturday morning, perhaps a lingering shower or storm possible over the eastern zones early on, otherwise dry behind the cold front. A high risk for rip current development at ocean beaches is likely for Friday afternoon due to southerly wind waves increasing to 3 to 5 ft and a residual 2 ft se swell. Regarding the heat, both days are progged to have 18-19C temperatures at 850MB. Saturday, with lower boundary layer dewpoints and a better chance of mostly sunny conditions, is currently forecast to be slightly warmer than Friday. But since surface dewpoints will probably have a harder time mixing out during Friday, heat index values will be higher on Friday. There is potential that a heat advisory will be needed across the city for this period, however Saturday`s heat indices are currently forecast to barely meet the criteria. The rest of the forecast area should remain below advisory criteria. Sunday will feature dry and mostly sunny conditions with weak high pressure over the area. Temperatures aloft drop a little, and surface dewpoints should be able to mix out again, so heat indices should be below 95 for just about everywhere. Another cold front approaches on Monday, but a warm front pushes through first. This will bring higher dewpoints across the area, and with 850MB temperatures forecast to be 19-20C, heat indices of 95- 100 could be widespread. Just like on Friday, there is some uncertainty for high temperatures due to potential thunderstorm activity and related cloud cover. 850MB temperatures don`t look to drop off all that much, if at all on Tuesday. Surface dewpoints will probably be lower, but heat advisory criteria could be met once again in the city for the Monday- Tuesday period. High pressure looks to continue the dry weather pattern on Wednesday. High temps and heat indices are forecast to be below 95. && .AVIATION /06Z THURSDAY THROUGH MONDAY/...
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High pressure centered over western Pennsylvania into West Virginia drifts east overnight, and moves off the Mid- Atlantic coast early Thursday morning. The high remains offshore into Thursday night. VFR through the TAF period. Southwest winds under 10 KTS at the metro terminals overnight, with outlying terminals light and variable. SW winds increase Thursday morning with sea breezes developing in the afternoon. .OUTLOOK FOR 06Z Friday through Monday... .Thursday night through Friday morning...VFR. .Friday afternoon through Friday night...MVFR or lower possible in SCT TSRA. S-SW winds 15-20 KT with 25 KT gusts across NYC and Long Island. .Saturday through Sunday...VFR. .Monday...MVFR or lower possible in SCT TSRA.
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&& .MARINE... High pressure builds slowly east of the waters through Thursday night with a frontal system dropping SE across the Great Lakes. Southerly flow strengthens Thursday afternoon/night with gusts up to 20 kt possible on the ocean waters with seas building to around 4 ft. At this time, expect winds and seas to remain below SCA. A tightening pressure gradient ahead of a cold front will probably bring winds and seas to advisory criteria levels on the ocean waters Friday afternoon into Saturday morning. For the other waters, meeting criteria during this period appears to be more marginal, but currently have 25 KT gusts in the forecast for the eastern sound Friday afternoon and night. Sub-sca conditions then prevail across all waters for the rest of the forecast period. && .HYDROLOGY... No adverse hydrologic impacts are anticipated with scattered showers and thunderstorms Friday/Friday night and Monday/Monday night. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...JC/DW NEAR TERM...NV/DW SHORT TERM...DW LONG TERM...JC AVIATION...BC/MET MARINE...JC/NV/DW HYDROLOGY...JC

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