Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 171403 AFDOKX Area Forecast Discussion National Weather Service New York NY 1003 AM EDT Thu Aug 17 2017 .SYNOPSIS... High pressure over the northeast and mid Atlantic states will drift offshore today. A warm front will approach this evening and move north late tonight into Friday morning. A cold front approaches Friday, moving across the region late Friday night into early Saturday. High pressure returns on Sunday into Monday before a series of troughs and a cold front pass through Tuesday into Wednesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Quiet weather conditions this morning. Minor updates to temperatures and dewpoints based on latest observations. The rest of the forecast is still mainly on track. An upper ridge axis will remain west of the region most of the day, moving into the northeast around 00Z Friday. Meanwhile surface high pressure centered over upstate New York will drift to off the northeast and mid Atlantic coasts. The next shortwave to affect he region will move into the Great Lakes region. The upper flow will be somewhat blocky as the ridge builds and moves slowly east. Will be dry with increasing clouds late in the day as the ridge axis moves into the region. There is a moderate risk for the development of rip currents at the ocean beaches today. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/... The upper ridge axis passes to the east and builds tonight into Friday night as the upper pattern remains rather blocky as heights rise as the ridge moves into the northern Atlantic. This will keep the shortwave from moving east and lifts into southern Canada and weakens as yet another moves into the upper mid west and then into the Great Lakes region Friday night. At the surface low pressure over the upper midwest will rotate slowly into Ontario and western Quebec through Friday night. A weak warm frontal boundary increases today and slow approaches from the southwest this evening. Precipitation will be delayed until late tonight as the warm front slowly pushes into the region as the parent low remains well to the west. Best chances or precipitation will be across northeastern New Jersey into the Lower Hudson Valley. The region becomes warm sectored Friday as the warm front lifts through. CAPE and surface based instability increase during the day as the cold front slowly approaches. There may be a break in the precipitation of a brief time once the warm front lifts north, and until the cold front nears later in the day. Best instability will be inland as a deep southerly flow keeps a marine layer across Long Island and into southern Connecticut. Best chances of thunderstorms, possible strong, will be inland Friday afternoon into the evening. Then the storms will weaken and move into Long Island and southern Connecticut Friday night. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Cold front moves through the area during Saturday with a chance of lingering showers and thunderstorms in the morning. Models then agree that the available moisture is probably too low for consideration of afternoon showers and storms, especially since a lagging upper trough and shortwave appear to be too late to arrive for necessary lift and mid level instability. Will therefore go with a dry forecast for the afternoon. Then with stabilizing lower levels, the upper trough should pass through dry during Saturday night. An even blend of MAV/NAM MOS looked good for temperatures. High pressure builds in on Sunday and lasts into Monday as the upper flow becomes zonal to anticyclonic. Dry weather for both days with highs mostly in the mid 80s. For Tuesday into Wednesday, low pressure tracks across southeastern Canada. This will bring a couple of pre-frontal troughs here before a cold front eventually passes through sometime most likely on Wednesday. Looks like the best combination of moisture, lift and shear could be late day Tuesday into Tuesday night. Will cap PoPs at chance Tuesday through Wednesday for now given the timing uncertainty of the surface features and sources of lift aloft. Highs generally in the 80s both days. && .AVIATION /14Z THURSDAY THROUGH MONDAY/... High pressure will slide offshore today before a warm front approaches from the southwest tonight. VFR through the TAF period. Light northeasterly winds will veer to the southeast between 17-18Z as the high shifts offshore. KLGA may remain NE for a bit longer before turning SE. 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: Timing of wind shift to SE could be off by +/- 1 hour. The afternoon KJFK haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KLGA TAF Comments: Timing of wind shift to SE could be off by +/- 1 hour. The afternoon KLGA haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KEWR TAF Comments: Timing of wind shift to SE could be off by +/- 1 hour.No unscheduled amendments expected. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Timing of wind shift to SE could be off by +/- 1 hour. KHPN TAF Comments: Timing of wind shift to SE could be off by +/- 1 hour. KISP TAF Comments: Timing of wind shift to SE could be off by +/- 1 hour. .OUTLOOK FOR 06Z FRIDAY THROUGH MONDAY... .Thursday night through Saturday night...MVFR or lower flight cat possible in showers/tstms. .Sunday And Monday...VFR. && .MARINE... Swells and seas have subsided on the ocean waters, and with high pressure moving across the waters today, winds and seas remain below small craft advisory levels. A warm front approaches the waters today and moves north late tonight into early Thursday morning. Southerly winds will be increasing ahead of an approaching cold front Friday. And with the increased winds, mainly west of Fire Island Inlet, and with the Ambrose jet, ocean seas may briefly build to around 5 feet late Friday afternoon into Friday evening. Will hold off on issuing an advisory being late in the third period and with some uncertainty. Otherwise, winds and seas remain below advisory levels into Friday night as a cold front moves into the forecast waters. The cold front should cross the waters through the day on Saturday with slowly subsiding seas and winds remaining below SCA levels. Sub- SCA conditions then continue into Sunday and Monday as high pressure builds in over the waters with a weak pressure gradient. && .HYDROLOGY... A prolonged period of rainfall is likely from late tonight into Saturday morning, with around 1 inch possible across the region, with locally higher amounts. Locally heavy rainfall is possible Friday and Friday evening. At this time it remains difficult to pinpoint where heavier showers and thunderstorms will develop. No significant hydrologic impacts are expected, but some minor urban flooding is possible. Impacts from potential showers and thunderstorms Tuesday into Wednesday are uncertain at this point, however at least minor nuisance flooding will remain a possibility. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$

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