Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 181540 AFDOKX Area Forecast Discussion National Weather Service New York NY 1140 AM EDT Fri Aug 18 2017 .SYNOPSIS...
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A cold front will slowly move east across the area late tonight, but will linger across the eastern end of Long Island and Southeast Connecticut. The front will not totally clear the region until Saturday night. High pressure will then build in through the beginning of next week, followed by a midweek cold frontal passage.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Heavy showers with embedded thunderstorms will move east across Eastern Long Island and SE CT through 1 pm. Hourly rates in excess of 1.5 inches per hour have caused flash flooding in parts of Suffolk County and widespread minor to locally moderate flooding from the NJ/NYC Metro area east this morning. Satellite imagery shows a SW/NE dry slot advecting NE from VA/MD across SE PA, that should advect NE across the Lower Hudson Valley by 18z. This will increase sfc based and low lvl instability resulting in the development of convection mainly aft 20z this afternoon from SW to NE. The highest chc for severe wx will be from NYC N and W, where SPC placed this area under a Slight Risk. The greatest threat is for damaging wind gusts. Stay tuned. Because precipitable water values remain high -- close to 2 to 2.2 inches, heavy rain causing mainly urban flooding will remain possible. There is a moderate risk of rip currents at ocean beaches, potentially becoming high this afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... Models at times can struggle with the precipitation forecast with the departure of large mid level ridges above 580dm. So, forecast will adjust for this in situation where there is more forcing and precip is too low and vice versa. The upper level trough will be approaching the region tonight. The height falls become more remarkable late tonight into Saturday morning and this is when the trough moves eastward a greater distance. The region will be getting closer to the right entrance region of this jet. The trough amplifies and shortens its wavelength during the day Saturday. 500mb heights lower 20-30 m from early morning until early evening. Vorticity still increasing with height tonight and Sat looking at 925, 850, and 700mb levels. Still have a threat of gusty winds and heavy rain with thunderstorms tonight. High precipitable waters near 2 inches still will be in place as will the vertical wind shear. A cold front will continue to approach tonight. The cold front moves into the region late tonight into Saturday but does not totally clear the region until Saturday night. However with aforementioned dynamics, pops still in place for parts of the CWA during Sat evening with possibility for isolated shower activity. West to Northwest flow behind the cold front later Saturday night and continued ridging will promote mainly dry conditions. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Shortwave trough pivots northeast of the region on Sunday, with generally zonal upper flow over the region for early to mid of next week, between southern ridging and a closed low moving into Hudson Bay. At the surface, high pressure builds into the region Sunday, and then gradually sinks south and east of the region Monday into Tuesday. The result will be dry and seasonably warm conditions on Sunday, giving way to increasing heat and humidity Mon into Tue. Perhaps some afternoon shower/tstm activity along a lee trough Tue afternoon depending on any energy sliding through the upper flow aloft, but low predictability at this point. Decent model agreement with shortwave energy digging into the Great lakes Tue into Tue Night and then towards the NE US on Wed. An associated frontal system will bring the next chance for organized shower and tstm activity late Tue into Wed. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/...
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A cold front approaches late today. Showers and thunderstorms have worked their way out of the city and are across the eastern half of the terminals late this morning. However, MVFR/IFR ceilings continue in the wake. Some improvement is likely this afternoon before another round of showers and thunderstorms arrives around 21z. Thunderstorms are likely this evening with the cold front approaching until about 01z. Gusty winds and heavy rain possible in any thunderstorm. Southerly winds will increase this afternoon, mainly between 10 to 15 kts. Gusts to 25 kt possible across much of the region this afternoon, but especially along the coast. Higher gusts possible with any thunderstorm. For tonight, fog/stratus with MVFR or lower conds may linger through the overnight. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: MVFR cigs could prevail. Amendments possible for timing and coverage of showers and thunderstorms this this afternoon and evening. The afternoon KJFK haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KLGA TAF Comments: MVFR cigs could prevail. Amendments possible for timing and coverage of showers and thunderstorms this afternoon and evening. The afternoon KLGA haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KEWR TAF Comments: MVFR cigs could prevail. Amendments possible for timing and coverage of showers and thunderstorms this afternoon and evening. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: MVFR cigs could prevail. Amendments possible for timing and coverage of showers and thunderstorms this afternoon and evening. KHPN TAF Comments: MVFR cigs could prevail. Amendments possible for timing and coverage of showers and thunderstorms this afternoon and evening. .OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY... .Saturday-Monday...VFR. light NW wind becoming SW by Late Sunday and Monday. .Tuesday...Iso shra/tstms possible with MVFR or lower conds...otherwise VFR.
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&& .MARINE... SCA on ocean today through tonight with sub SCA on other waters. Overall sub SCA conditions expected Sat and Sat night with offshore flow developing behind cold front. Winds and seas are expected to remain blw sca lvls on all waters Sun thru Wed as high pressure builds across the waters. && .HYDROLOGY...
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Heavy showers and thunderstorms resulted in 1 to 3 inches of rain this morning from the Metro NJ/NYC area east across Long Island. Another round of heavy showers and thunderstorms will be possible this evening ahead of the cold front. Rainfall accumulations are expected to be around a half an inch to an inch, with locally higher amounts possible in thunderstorms. It still remains difficult to pinpoint where heavier showers and thunderstorms will develop. There is a chance of flash flooding with the more likely flooding hazard being minor flooding of poor drainage and urban areas especially tonight with places that received heavy rain during the morning. Impacts from potential showers and thunderstorms Tuesday into Wednesday are uncertain at this point.
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&& .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ350-353- 355. && $$ SYNOPSIS...JM/NV NEAR TERM...GC/JM SHORT TERM...JM LONG TERM...NV AVIATION...IRD MARINE...GC/JM/NV HYDROLOGY...GC/JM/NV

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