Area Forecast Discussion
Issued by NWS Upton, NY

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763 FXUS61 KOKX 222009 AFDOKX Area Forecast Discussion National Weather Service New York NY 409 PM EDT Sun Oct 22 2017 .SYNOPSIS...
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Dry and mild today as high pressure pulls away from the region. A slow moving frontal system will impact the region Tuesday into Wednesday with strong winds gusts and potentially heavy rain. A frontal system slowly moves east Wednesday into Wednesday night. An upper level disturbance passes Thursday before high pressure returns for the end of the week.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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Strong western Atlantic upper ridging will remain in control. At the surface, high pressure slowly drifts east of the New England coast with an increasingly moist s/se flow. Moistening under a subsidence inversion should allow for patchy stratus and fog development overnight. After early radiational cooling across far outlying areas, where stratus develops it would stabilize or raise temps late tonight into early Mon Morning. Lows generally in the 40s across far outlying areas, 50s coast, to around 60 for NYC metro (close to normal highs for this time of year).
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH TUESDAY NIGHT/...
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Models in good agreement with strong western Atlantic ridging slowly shifting offshore, as vigorous PAC shortwave/jet energy digs through the Central US Monday and all the way to the Gulf coast by Tuesday Night/Wed. The resultant -3 to 4 STD deep eastern US longwave trough will then tilt towards the NE US for Midweek. Its associated frontal system will approach the region Monday night, and then crawl across the region Tue into Wed in the longitudinally oriented steering flow. Trend with this system has been slower based on the upper pattern and dprog/dt. Moisture remains relatively shallow on Monday afternoon into Monday Night, with lighter rain shower activity, as well as stratus/drizzle development. Moisture and forcing increases Tuesday as the frontal system approaches, presenting the following potential hazards Tuesday into Wednesday: Heavy Rain: The slow movement of the front, deep lift (potentially right rear of 150+ kt jet streak), weak instability, and interaction with an increasingly moist and tropical airmass (+3 to 4 std) signal potential for multiple bands of heavy rain as weak waves lift north along the front. Lower resolution ensembles continue to range between 1 1/2 to 3 inches of rain Tue thru Wed. Higher res operational NAM/GFS and SBUWRF models indicating potential for localized swaths of 3-4 inches, much of which falls in a 6 hr period. This looks to be a credible threat based on synoptic pattern, but location/timing is very much uncertain based on front and frontal wave timing and location. See hydrology section for associated flooding threat. Strong Winds: The other potential hazard is for strong winds during the Tue into Tue Night period as a 50-60 kt 950 hpa llj moves overhead Tue afternoon into Tue NIght. NAM/GFS BUFKIT soundings indicating a 12-15 hr period of southerly winds gusts of 30 to 40 mph, with potential for any low topped convective line/s ahead of the cold front being able to drag down localized 45-55 mph wind gusts to the surface.
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&& .LONG TERM /WEDNESDAY THROUGH SUNDAY/...
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A deepening negative tilting trough will move into the region Wednesday through Wednesday night. A stalled cold front in the region Wednesday into Wednesday night will shift slowly eastward as a wave of low pressure travels northeastward along it late Wednesday night into Thursday, allowing the front to move across late Wednesday night. The trough axis moves across Thursday and well northeast of the region Thursday night. The front moves slowly farther east of the region Thursday into Thursday night. High pressure then moves in on Friday and quickly goes offshore, shifting eastward heading into the start of next weekend before another frontal system approaches for next Sunday. Thunderstorms chances will be slight Wednesday morning for eastern sections of the region, highest omega and elevated instability will be shifting from SE CT and Eastern Long Island to east of the region later Wednesday morning. Rain showers could still be heavy at times Wednesday morning. The rain showers will linger the whole day across much of the region and even into the night, but that will be mainly for Long Island and Southern CT. Winds will be trending down as the frontal zone will be right across the region with the pressure gradient being rather diffuse and weak. Rain shower chances continue into Thursday behind the cold front but coverage and probabilities will be lower than before as westerly flow will promote more dry conditions. The factors still favoring a chance of showers though will be the cold pool aloft and mid level omega associated with the upper level trough axis moving across. Drier low level conditions will keep showers light without much QPF. Dry weather will then return Thursday night through Saturday as upper level ridging becomes strong as it quickly moves offshore. The surface high pressure area quickly moves offshore as well and will not be that strong, but should keep the dry weather along with another warming trend with SW flow increasing in the atmospheric column. Temperatures overall will continue to average at least few degrees above normal for the rest of the week.
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&& .AVIATION /20Z SUNDAY THROUGH FRIDAY/...
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VFR through at least 06z Mon as high pres gradually moves east through tonight. S/SE winds 8-12 kt late today from seabreeze enhancement at coastal terminals. Aft 06z tonight may start seeing indications of fog and/or stratus development mainly away from the city terminals. Better chance of stratus would hold off until Monday morning with ceilings probably VFR or MVFR when it occurs. .OUTLOOK FOR 18Z MONDAY THROUGH THURSDAY... .Mon...VFR likely, chc MVFR cigs. S/SE G20 kt Mon aftn. .Mon night-Tue...Potential period of S/SE G30-40 KT with LLWS SSW 45-55kt@2kft for coastal terminals. MVFR/IFR developing in -RADZ Mon night, continuing with SHRA and low prob/sparse TSRA Tue. .Tue night-Wed...IFR possibly continues in SHRA Tue night, low prob/sparse TSRA early evening, improving to MVFR and possibly VFR by late Wed. .Wed night-Thu...VFR, with iso-sct MVFR in SHRA. .Fri...VFR.
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&& .MARINE...
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Quiet conds on all waters through Mon as high pressure over the area slowly shifts east. The pressure gradient will begin to tighten Mon Night as low pressure strengthens over the Great Lakes. SCA conds are expected to develop Mon night with the potential for marginal gale force gusts Tue into Tue night on all waters. High seas are expected to develop n the ocean. Will hold of on 4-5th period gale watch...based on marginal potential and perhaps more convectively correlated. Winds subside late Tueday night into Wednesday morning int the wake of the frontal system. SCA conditions will still be probable across all ocean and Eastern waters Wednesday morning due to both winds and for the ocean, the high seas as well. For Wednesday afternoon and thereafter, SCA conditions will linger on the ocean mainly due to the high seas. The non-ocean waters are forecast to have below SCA conditions.
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&& .HYDROLOGY...
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A widespread 1 1/2 to 3 inches of rain is likely Tuesday into Wednesday morning, with locally 3 to 4 inches. Concern is that much of this rain could fall in a 6 hr period in slow moving and/or training bands of low topped convection/heavy rain, but the predicatability on location of where this occurs is low. Despite antecedent dry conditions, these potential rainfall rates present an areawide potential for minor urban and poor drainage, with a localized threat for flash flooding. In addition, if the heavier rain amounts occur over Northeastern New Jersey and the Lower Hudson Valley, rapid rises in flashy small streams and minor flood impacts to adjacent areas would be plausible. Heavy rain threat diminishes Wednesday afternoon, with drying conditions expected Thursday night through Saturday.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 3 AM to 8 PM EDT Tuesday for ANZ330- 335-338-340-345. Small Craft Advisory from 10 PM Monday to 8 PM EDT Tuesday for ANZ350-353-355.
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&& $$ SYNOPSIS...JM/NV NEAR TERM...NV SHORT TERM...NV LONG TERM...Tongue AVIATION...JC/JP MARINE...JM/NV HYDROLOGY...JM/NV

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