Area Forecast Discussion
Issued by NWS Upton, NY

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160 FXUS61 KOKX 231443 AFDOKX Area Forecast Discussion National Weather Service New York NY 943 AM EST Mon Jan 23 2017 .SYNOPSIS... Strong low pressure over the Tennessee Valley this morning will emerge off the Mid Atlantic this afternoon becoming a major coastal storm as it tracks slowly northeast. The low passes to the south and east of Long Island Tuesday into Tuesday night. High pressure will build in the wake of the storm on Wednesday. A series of weak, mainly dry cold fronts will move southeast around low pressure north of New England through Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Updates include slowing down the onset of likely PoPs for certain locations, but also to include the mention of sleet and snow chances for the remainder of this morning into early afternoon over the higher elevations of interior CT and Putnam county. There appears to be just enough moisture aloft for ice nucleation with the warm nose just cold enough to support snow as a PCPN type. A strong southern branch upper low over the Tennessee Valley this morning will send a deepening surface low off the Mid Atlantic coast this afternoon. The low will work slowly north and east through Tuesday, passing south and east of New England. At the same time, a departing northern branch upper trough across eastern Canada will be followed by strong surface high pressure. This will set the stage for strong Northeast winds, heavy precipitation,and urban, small stream, and coastal flooding. Models are in good overall agreement with the track and intensity of the low with some small differences. The biggest concern relates to thermodynamics with the cold air drainage ahead of the storm through tonight, and then warming aloft as the low wraps in warmer air off the Atlantic. The timing of the warming could have significant consequences for areas well north and west of NYC which are under a Winter Weather Advisory. Those areas will likely see a light mix of rain and sleet today, with mainly rain elsewhere. The low continues to trend slower, thus the delay in heavy precipitation to late this afternoon into this evening. Rainfall amounts today may approach a quarter inch by evening. The main story is going to be high winds, specifically at the coast which could see gusts up to 60 mph by late afternoon. An anomalously strong easterly jet will gradually strengthen ahead of the low, peaking at around 70 kt at 925 mb just south of LI this evening. The NAM is strongest with the jet and is preferred in this scenario. Thermo profiles shows mixing up to 925 mb, which supports a good percentage of these winds mixing down to the surface. High Wind Warnings remain up at the coast, with Wind Advisories up for much of the interior. A strong cold air damming signature on the east side of the Appalachians with a strong NE flow will allow for temperatures to gradually fall today, with most locations into the mid and upper 30s by late this morning. Mid level dry air and wet bulb temperatures near or below zero in the interior will allow for some sleet to mix in with any light rain.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Best thermal forcing and dynamics will be across the area the first half of tonight with heavy precipitation and high winds. There is the potential for in 1 to 1 1/2 inches of rainfall by early morning, with the rain decreasing in intensity toward daybreak. A Flood Watch remains up for the NYC metro, southern portions of the Lower Hudson Valley, and coastal SW Connecticut. This is mainly for urban and small stream flooding concerns, especially if localized rainfall amounts exceed 3 inches. In addition, should the heavy rain coincide with the high tide, this will exacerbate any flooding. This includes locations along tidally affected rivers, such as the Passaic, Hackensack, and Hudson. As previously mentioned. temperature profiles will be critical to the northwest of NYC, as the heavy precipitation falls in a marginally cold airmass. Deep-layered lift and column cooling will result in a period of moderate to heavy snow across portions of Orange and Putnam counties in the Lower Hudson Valley, and western Passaic in Northeast NJ. Eventually, enough warm air aloft comes in late tonight for a transition back to rain. Timing is everything here. Should the heavy precipitation fall as snow for a longer period of time, snowfall totals would be higher than currently forecast, and vice versa if more as rain. Right now, those locations under a winter weather advisory are forecast to see 2 to 4 inches of snow and sleet with perhaps a light coating of ice. Winds and heavy precip should fall off late tonight with some rain lingering into Tuesday as the low has trended slower in the models. The slow moving storm will pass on Tuesday. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Tuesday night until Midnight...Light precipitation will end from west to east as low pressure moves east of coastal New England. The highest chc for mixed precip will be across our far west zones and across higher elevations NW of NYC. However, we are not anticipating any significant accumulations. Wednesday and Thursday...A weak ridge of high pressure will move quickly east across the region early Wednesday followed by a long wave of low pressure thru the day Thursday. No sensible weather is forecast as temps cont to avg above normal in SW flow. Friday through Sunday...signals a weather pattern change as a ridge builds across western North America and a trough develops across the Eastern U.S. This will bring colder temps across the area to close out January. && .AVIATION /15Z MONDAY THROUGH FRIDAY/... A deep low centered over the southeastern states will track slowly to the northeast today, emerging off the Mid Atlantic coast by 00Z Tuesday. The low then tracks slowly northward along the coast Monday night. Winds will be the primary issue through the TAF period. Northeast winds will increase throughout the day, peaking at around 30 kt sustained, with gusts to 45-50 kt late this afternoon into this evening. There is a chance of occasional gusts to near 60 kt at coastal terminals this afternoon and this evening. Winds will begin to slowly diminish after 00Z and become more northerly as the low passes to the south and east. While the bulk of the precipitation should hold off until after 18Z on Monday, with plenty of low level moisture light rain or drizzle is likely at times Monday morning. Precipitation will fall in the form of rain for the city and coastal terminals, with an outside chance of rain mixing with sleet as precipitation starts this afternoon at KHPN. Rain could be heavy at times tonight. At KSWF, a mix of rain and sleet is possible to start, becoming a mix of heavy snow and sleet late in the day. Snow and sleet could total 1 to 2 inches by tonight, with higher accumulations possible if the precipitation falls primarily as snow. Primarily MVFR ceilings this morning will persist into the afternoon before falling to IFR as the rain moves in and becomes heavy late this afternoon and this evening. 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: Amendments possible this morning for changes in ceiling. Occasional gusts to near 60 kt are possible this afternoon and evening. KLGA TAF Comments: Amendments possible this morning for changes in ceiling. KEWR TAF Comments: Amendments possible this morning for changes in ceiling. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Amendments possible this morning for changes in ceiling. KHPN TAF Comments: Amendments possible this morning for changes in ceiling. KISP TAF Comments: Amendments possible this morning for changes in ceiling. Occasional gusts to near 60 kt are possible this afternoon and evening. .OUTLOOK FOR 12Z TUESDAY THROUGH FRIDAY... .Tuesday-Tuesday night...IFR ceilings to start. Rain will come to an end beginning late Tuesday afternoon with conditions improving during the evening to VFR southwest to northeast. Winds NE backing to NW during the day. .Wednesday and Thursday...VFR. SW Winds 15-25 kt. .Friday...VFR. W 15-25 kt. && .MARINE... An intensifying storm moving up the coast will bring storm to marginal hurricane force wind gusts to the ocean waters late this afternoon into this evening. On the non-ocean waters, storm warnings remain in effect. Expect peak winds 50-60 kt where storm warnings remain. Before then, gales are likely to develop quickly tonight, followed by storm force winds developing from south to north through the day on Monday. Max seas could peak at 20-22 ft on the ocean, 9-12 ft from Orient Point east, and 8-9 ft on central Long Island Sound, per combo of WaveWatch/NWPS guidance and wind/wave climatology. Marine Long Term... .Tuesday through Wednesday Afternoon...Seas will gradually subside as winds become SW at 15-20kt by Wednesday Afternoon. .Wednesday Night...Winds and seas decrease below Small Craft Advisory levels. .Thursday and Friday...Winds and seas increase to SCA on the Ocean with the approach and passage of a cold front. && .HYDROLOGY... QPF late today through tonight will likely be in the 1-2 inch range, with locally higher amounts possible with the heaviest rainfall. If high end rainfall amounts are realized, this will bring a threat for moderate urban flooding and minor small stream flooding in NE NJ and the Lower Hudson Valley. This will be exacerbated by coincidence of high tide with heavy rain Mon eve along coastal waterfront and shoreline roads...including along tidally affected rivers. Potential for minor flooding on larger rivers is slight. && .TIDES/COASTAL FLOODING...
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For the late afternoon/evening tide, expect widespread minor to areas of moderate coastal flooding. Primary attention remains for the late afternoon/evening high tide cycle. Moderate coastal flooding expected along southern and eastern bays of LI, Staten Island, low-lying north and east facing coastlines along Western LI Sound, and the Atlantic beachfront due to the combination of elevated water levels and wave action. There is a low potential for major flood thresholds to be reached in the most vulnerable Great South Bay communities such as Lindenhurst and Freeport. A coastal flood warning remains in effect to address this flood threat. Elsewhere minor to locally moderate coastal flooding expected. Minor to locally moderate coastal flooding could linger for the southern and eastern bay areas for the Tuesday morning high tide cycle as well, including the lower NY Harbor. An ensemble of guidances is showing potential for surge to build to 3 1/2 to 4 1/2 ft by this evening. These latest numbers are close to yesterday`s guidance, with some differences noted in a few spots. The evening expected surge is in line with surges seen during a March 13th 2010 event with similarities in wind/wave forcing. The other concern will be for widespread dune erosion and localized washovers at Atlantic ocean beaches from elevated waters levels and an east to west sweep of 8 to 14 ft surf today into Tue.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...High Wind Warning until 1 AM EST Tuesday for CTZ009>012. Flood Watch from 1 PM EST this afternoon through late tonight for CTZ009. Wind Advisory until 1 AM EST Tuesday for CTZ005>008. Coastal Flood Advisory from 5 PM this afternoon to 11 PM EST this evening for CTZ009>012. NY...High Wind Warning until 1 AM EST Tuesday for NYZ071>075- 078>081-176>179. Coastal Flood Warning from 3 PM this afternoon to 11 PM EST this evening for NYZ079>081-179. Winter Weather Advisory from 1 PM this afternoon to 7 AM EST Tuesday for NYZ067-068. Flood Watch from 1 PM EST this afternoon through late tonight for NYZ069>075-176>179. Wind Advisory until 1 AM EST Tuesday for NYZ069-070. Coastal Flood Advisory from 3 PM this afternoon to 9 PM EST this evening for NYZ072-075-178. Coastal Flood Advisory from 5 PM this afternoon to 11 PM EST this evening for NYZ073-176. Coastal Flood Watch from late tonight through Tuesday morning for NYZ080-179. Coastal Flood Advisory until 3 PM EST this afternoon for NYZ080-179. Coastal Flood Advisory from 11 PM this evening to 1 AM EST Tuesday for NYZ080-179. Coastal Flood Warning from 7 PM to 11 PM EST this evening for NYZ071-078-177. Coastal Flood Warning from 3 PM this afternoon to 7 PM EST this evening for NYZ074. NJ...High Wind Warning until 1 AM EST Tuesday for NJZ006-106-108. Winter Weather Advisory from 1 PM this afternoon to 7 AM EST Tuesday for NJZ002. Flood Watch from 1 PM EST this afternoon through late tonight for NJZ004-006-103>108. Wind Advisory until 1 AM EST Tuesday for NJZ004-103>105-107. Coastal Flood Advisory from 3 PM this afternoon to 9 PM EST this evening for NJZ006-106-108. MARINE...Storm Warning until 1 AM EST Tuesday for ANZ330-335-338-340- 345. Hurricane Force Wind Warning from 1 PM this afternoon to 1 AM EST Tuesday for ANZ350-353-355.
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&& $$ SYNOPSIS...DW NEAR TERM...JC/DW SHORT TERM...DW LONG TERM...GC/DW AVIATION...FEB MARINE...DW HYDROLOGY...DW TIDES/COASTAL FLOODING...PW/NV

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