Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 202336 AFDOKX Area Forecast Discussion National Weather Service New York NY 636 PM EST Fri Jan 20 2017 .SYNOPSIS...
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An upper level disturbance weakens tonight as the disturbance moves through the region. High pressure briefly returns on Saturday. Deepening low pressure moving across the southern states on Sunday will reach the southern Mid Atlantic region by Monday morning, while high pressure builds southeast into the Canadian Maritimes. The low will intensify into a significant coastal storm as it moves up the coast toward the area Monday through Tuesday. High pressure builds for Wednesday as the coastal low departs towards New England. A cold front slowly approaches the area from the west, moving through late Thursday.
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With the weakening upper level disturbance the precipitation associated with the shortwave has been also weakening and diminishing in areal extent. Latest guidance has heights beginning to rise across New Jersey and into the western portion of the forecast area 01Z to 03Z and the precipitation ending a couple of hours sooner across the western half of the area. Guidance seems to handling the trends well and updated the probabilities through tonight. Temperatures, dew points, and winds remain mostly unchanged, with just minor adjustments across eastern Long Island where temperatures remain in the lower 40s. Low-level ridging is still lingering, and with added moisture from the rain expect stratus, possibly areas of light drizzle and some patchy fog, will continue through the night. Extensive cloud cover and weak warm advection will support low temperatures in the mid 30s to lower 40s, 15-20 degrees above climatological normals.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... High pressure briefly builds across the area for Saturday. Light drizzle and patchy fog will gradually end by morning as the flow strengthens from the west-southwest. Subtle downslope flow and subsidence will support high temperatures in the 50s, well above normal for this time of year. With the low-level inversion remaining in place, stratus will linger once again. If clouds do eventually erode with the subsidence, then temperatures may potentially be a few degrees warmer than forecast. Similar conditions are expected overnight with cloud cover and weak warm advection once again leading to well above normal lows around 40. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Significant coastal storm likely Sunday Night into Tuesday with potential high wind...heavy rain...and coastal impacts. Main focus is on this storm forecast to take shape as strong Pacific jet energy is currently crashing onshore the California coast...allowing an upper level system to close off over the southern plains this weekend and then negatively tilt up the east coast Monday into Tuesday. The result will be strong low pressure tracking through the southern states this weekend...and then tracking up the coastal plain towards the area Mon/Tue. Models in general agreement with the synoptic fields...but considerable spread exists in timing/track/intensity of the closed upper low as it moves up the coast...which is playing out in model spread on track/speed of the surface low Mon/Tue. This is particularly seen in the timing of coastal low development and eventual development into the primary low. SBU ensemble sensitivity still pointing towards a strong wave packet emanating from shortwave energy that came off the eastern Asia coast last night. Have stayed close to an ensemble mean with forecast...with general agreement in low pressure tracking over or just se of Li Late Monday Night/Tue. Potential exists for multiple impacts of strong winds, heavy rain (wintry mix NW) and minor to locally moderate coastal flooding, with likelihood of occurrence in that general order. In terms of winds...GEFS signaling an easterly llj 5-6 std above climo. EPS probabilities for wind gusts over 50 kt have increased to categorical for Mon/Mon night for the immediate coastline, and the extended 00z/12Z GFS/ECMWF MOS guidance indicate sustained winds 30-35 kt along the coast. This signals a high potential for wind advisory conditions for the coast and low potential for high wind...peaking Mon aft/eve. See coastal flood sections for potential coastal flood impacts. In terms of heavy precip...PWATs of 3-4 stds above climo continue to be signaled as the system taps into tropical connection to the Caribbean and Eastern Pacific. Coastal front development and orographic lift over western terrain should come into better focus over the next 48 hrs to pinpoint potential high end rainfall amounts and locations. Embedded convection not out of the question late Monday/Mon eve ahead of approaching closed low and with warm conveyor belt feeding into the region. Based on ensemble/operational output...likelihood for 1 to 3 inches of qpf with higher swaths possible. Based on strong dynamics and consensus storm track over or just se of LI...potential for thermal profiles to diabatically cool to near freezing and result in a period of rain/sleet/snow mix well N&W of NYC Late Sun Night into Mon night...with even a period of heavy wet snow across NW hills. A light snow/sleet accumulation is possible across interior portions of NE NJ...Lower Hud...and Southern Ct...with potential for an advisory level wet snow for the NW hills. Winds should fall off rather quickly Mon Night from sw to e as llj moves ne...with rain becoming more showery in nature overnight. Gradually improving conditions Tue into Tue Night as the upper low pivots ne and low pressure tracks up the New England coast. && .AVIATION /20Z FRIDAY THROUGH WEDNESDAY/... A wave of low pressure will move across the area tonight with high pressure returning for Saturday. MVFR cigs through the remainder of the afternoon with rain arriving. Rain continues through the evening with IFR conditions developing. Localized LIFR is possible. Some forecast guidance is hinting at residual low level moisture, which could result in areas of fog early Saturday morning. Winds remain light through the period at less than 10 kt. Wind directions will be Southeast, then South overnight. Some locations may become variable overnight. Winds then become Westerly on Saturday. ...NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: Timing of lower CIGs may be off by an hour or two. KLGA TAF Comments: Timing of lower CIGs may be off by an hour or two. KEWR TAF Comments: Timing of lower CIGs may be off by an hour or two. KTEB TAF Comments: Timing of lower CIGs may be off by an hour or two. KHPN TAF Comments: Timing of lower CIGs may be off by an hour or two. KISP TAF Comments: Timing of lower CIGs may be off by an hour or two. .OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY... .Saturday afternoon/night...MVFR or lower possible early Saturday morning, otherwise VFR. .Sunday-Sunday Night...MVFR or lower in light rain, then moderate rain at night. NE winds G20-30KT by late day, and G30-40KT later at night. .Monday-Monday Night...IFR conditions. Snow and rain for the interior including KSWF, and moderate-heavy rain elsewhere. ENE winds 25-30KT with G40-45KT. .Tuesday-Tuesday night...Rain tapering off in the afternoon/evening with improving ceilings. NW winds G25-35KT, highest in the morning. .Wednesday...VFR. && .MARINE... Seas will remain below SCA levels through Saturday night under a relaxed pressure gradient. An intensifying storm moving up the coast early next week will likely bring storm force gusts to the ocean and LI Sound...with potential for gusts even on nearshore waters Sunday night into Monday night. These winds have the potential to build seas to as high as 20 ft on the ocean waters, and 5-10 ft on LI Sound. && .HYDROLOGY... Likelihood of 1 to 3 inches, with locally higher amounts with a coastal storm Sun NIght into Monday...with heaviest rainfall Mon aft/eve. If high end rainfall amounts are realized...this will bring a threat for moderate urban flooding and minor small stream flooding in NE NJ/Lower Hud Valley. This would be exacerbated by coincidence of high tide with the heavy rain Mon eve. Rises on larger rivers would be likely...but at this point the potential for minor flooding appears slight. && .TIDES/COASTAL FLOODING... A strong coastal storm will likely cause 3 successive high tide cycles of minor coastal flooding Sunday Night into Monday Night...with potential for locally moderate coastal flooding with the Monday evening high tide. This moderate threat could linger into the early Tue morning high tide cycle. An ensemble of guidances is showing potential for surge building to 3 1/2 to 4 1/2 ft by Monday evening. The highest threat for coastal impacts will be for flood prone locales along the south shore bays of Li/NYC...eastern bays of LI...lower NY/NJ harbor including tidally affected rivers...and western Li Sound. The other concern will be for widespread dune erosion and localized washovers at Atlantic ocean beaches from long period easterly swells of 15-20+ ft Mon into Tue. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Storm Watch from late Sunday night through late Monday night for ANZ330-335-338-340-345-350-353-355. && $$ SYNOPSIS...MD/MET NEAR TERM...MD/MET SHORT TERM...MD LONG TERM...NV AVIATION...JC/JE MARINE...MD/MET/NV HYDROLOGY...MD/NV TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.