Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 212004 AFDOKX Area Forecast Discussion National Weather Service New York NY 404 PM EDT Sat Oct 21 2017 .SYNOPSIS...
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High pressure remains over the region through Monday. Strengthening low pressure heads northward into Southeast Canada Monday night into Tuesday with its associated cold front approaching the region. The cold front will slowly move into the region Tuesday into Tuesday night. The front will become nearly stationary Wednesday before gaining more eastward movement Wednesday night, moving east of the region by early Thursday. An upper level disturbance follows for Thursday before weak high pressure settles in late next week.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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High pressure ridge will be right over the area tonight. Winds will be light to calm as a result, but ideal radiational cooling conditions may be tempered by cirrus moving through. Expecting lows to be overall warmer than they were last night.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH MONDAY/...
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High pressure will be situated just offshore with another dry and mostly sunny day over here Sunday with only some cirrus filtering the sunshine at times. High temperatures will be above normal, but likely a couple of degrees cooler than yesterday in most cases. Low level moisture increases Sunday night with a light SE flow. Models suggest stratus moving in with better chances of at least a broken deck occurring west of eastern LI and CT. This leads to a partly to mostly cloudy Monday. There appears to be enough isentropic and low level lift for a chance of showers in the afternoon. Showers would be light as mid levels remain dry. Better chances are once again west of eastern LI and CT. In spite of the clouds and onshore flow, highs will still range mostly 70-75.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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Deep upper level trough with strong meridional flow will be approaching the region Monday night as the jet dives into the Southeast. The trough will stretch from Florida through Southeast Canada Tuesday into Wednesday. At the surface, the parent low pressure area moves from the Great Lakes Monday night into Northern Quebec by early Wednesday. With all steering flow going from south to north, the cold front will be slow moving, coming to almost a halt Wednesday before gaining more eastward movement Wednesday night in response to another upstream diving shortwave that is forecast to move NW to SE from the North Central US into the Carolinas. Thereafter, the upper level trough axis moves across Thursday while the surface cold front moves farther east into the Atlantic. Ridging and high pressure return but will be of lesser magnitude late next week. In terms of weather, rain showers will become more widespread Monday night into Tuesday, lingering into Tuesday night. Bulk of rain expected Tuesday afternoon through Tuesday night. The front nearly coming to a halt Wednesday will keep showers in the forecast Wednesday before tapering off Wednesday night. The region could even still see some showers Thursday with the upper level cold pool associated with the trough moving across. Models are hinting at this with their small QPF as the flow becomes more westerly. Then, mainly dry weather is expected Thursday night through next Saturday. Winds could potentially be an issue Tuesday through Tuesday evening. There is a low level jet ahead of the cold front and the models have pretty good agreement with the magnitude being near 50kt Tuesday into Tuesday night. With the deep trough and high precipitable waters forecast, near 1.75 to 1.8 inches, heavy rain will be possible at times especially in any thunderstorms. The thunderstorm chances will be there with strong omega and low level instability present within the model guidance. Low level instability is diagnosed from model CAPE fields between 100 and 300 J/kg. S-SE winds of 20-25 mph with gusts 30 to 40 mph are looking more probable especially along the coast with locally higher winds possible with any heavier showers or thunderstorms. Temperatures forecast of lower 70s for highs Tuesday and upper 60s to 70 for highs Wednesday. Highs more in the 60s for the rest of the days in the long term.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/...
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VFR expected through the TAF period as high pressure remains overhead tonight, then moves east Sunday. S/Se sea breeze around 10 kt at coastal terminals this afternoon, becoming light and variable tonight. S/SE winds 8-12 kt developing Sun afternoon. There is a low prob of MVFR-IFR fog late tonight at KSWF/KHPN/KGON/KISP. .OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY... .Late Sunday...VFR. S/SE seabreeze 8-12 kt for coastal terminals. .Sunday night-Monday...MVFR/IFR possible in stratus and fog Sunday Night. S/SE G20 kt Monday afternoon. .Monday Night-Tuesday...Potential for 6 hr period of S/SE G30-40 KT with LLWS SSW 45-55kt@2kft for coastal terminals. Could occur during morning push. MVFR/IFR developing in -RADZ Mon Night, continuing with RW and low prob/sparse TSRA Tuesday. .Tuesday Night-Wednesday...IFR possibly continues in showers Tue Night...improving to MVFR Wed. .Wednesday Night-Thursday...VFR, with iso-sct MVFR with shra. W/NW wind.
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&& .MARINE...
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Tranquil conditions on the waters tonight through Sunday night as high pressure ridge with a weak pressure gradient shifts offshore and slowly drifts out to sea. Onshore winds pick up through the day on Monday, but conditions will remain below advisory criteria. SCA becomes more probable Monday night on the ocean and likely Tuesday through Thursday on the ocean. Gales will be possible Tuesday and Tuesday night.
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&& .HYDROLOGY...
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Localized minor urban flooding will be possible Tuesday into Tuesday night but otherwise no other hydrologic problems are expected with the storm total rain of 1.5 to 2.5 inches mostly falling Monday night through Wednesday. Locally higher amounts will be possible.
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&& .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...JC/JM NEAR TERM...JC SHORT TERM...JC LONG TERM...JM AVIATION...NV MARINE...JC/JM HYDROLOGY...JC/JM

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