Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 251555 AFDOKX Area Forecast Discussion National Weather Service New York NY 1155 AM EDT Tue Apr 25 2017 .SYNOPSIS...
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Low pressure will slowly move up along the Eastern seaboard through Wednesday night, then head northeast into the Canadian Maritimes by the end of the week. A weakening frontal boundary will dissipate across the area on Friday. Another weak frontal boundary moving into the area Saturday into Saturday night will stall nearby early next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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High pressure to the north and low pressure along the Carolina coast has set up a maritime easterly flow. Warm front associated with the low will gradually work northward today. As the upper level low moves north along the eastern seaboard, moisture and lift will increase through the day. Stronger isentropic lift and deeper moisture work up the east coast ahead of the low late this morning and into the afternoon. Rain and drizzle will be periodic in nature, with some occasional lulls in activity, but model soundings do show pockets of elevated H6-9 instability with MUCAPE 200-400 J/kg, enough for some bands of brief locally heavy showers the first lifting up into southern CT early this afternoon, then another developing to the south and west mainly late. Mid level cap should prevent thunder. A fairly strong pressure gradient between the approaching low and the high to the north has brought breezy easterly flow through the day with gusts 20-25 mph. Temperatures will be in the 50s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/...
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Low level jet and a stacked coastal low will provide good lift tonight for widespread moderate to locally heavy rainfall. PW increases to near 200% of normal with values 1.50 inches. Models have come into a little better agreement with placement of heaviest QPF, but it is well known that QPF in models can be erratic. A very moist air mass, slow moving stacked low, low level jet, and elevated mid level instability as noted above support around 0.50-0.75 inches of rain on average across the area for the first half of the night. The low level jet will shift to the east after 06Z, which will focus the heaviest rain across eastern Long Island and southern Connecticut. On Wednesday, the stacked low will be slowly moving south and east of Long Island. Rain will continue across eastern Long Island and southeastern Connecticut, tapering off into the afternoon. Due to moisture wrapping around the low, cannot rule out light rain farther west as well. The close proximity of the stacked low should keep low clouds around through the day and possibly some patchy fog, so have gone with the cooler high temperatures in the lower 60s. It still appears that the entire CWA will fall short of flash flood and headwater guidance flooding for this event. See the hydrology section below for more details.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/... A dissipating upper low lifts NE along the New England coast at the onset of the period, otherwise a high amplitude upper ridge will prevail along the east coast through early next week. A series of weak frontal systems will converge upon the area, the first on Friday, which likely dissipates across the area. A backdoor cold front then may briefly drop south across the area Saturday night with a confluent flow aloft and shortwave trough moving over top the ridge across eastern Canada. 00Z ECMWF support GFS with the backdoor cold front making it through, even faster than the GFS on Saturday afternoon. Rain chances in both cases are low with ridging aloft and a capping inversion in place. Expect mainly showers, but an isolated thunderstorm is not out of the question. Strong and/or severe convection is not forecast at this time. Front returns north as a warm front Sunday night into Monday morning with a cold frontal passage Monday evening. There is the potential for stronger convection along and ahead of the cold front Monday. Anomalous upper ridge off the east coast over the the weekend into early next week will result in above normal temperatures and muggy conditions, with readings generally in the 70s and possibly the lower 80s, warmest across the interior. Conditions will be cooler along the immediate coast. Sunday and Monday may cool down a bit behind the backdoor cold front. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... Low pressure slowly moves up along the Mid-Atlantic coastline today and tonight. Conditions gradually deteriorate through the TAF period. Generally expect IFR cigs and visibilities, with LIFR possible at times through tonight. Intermittent rain, locally moderate to heavy at times today should lighten late tonight. East/northeast winds prevail, with speeds in the 15 to 20 kt range. Gusts will range 20 to 30 kt today and into tonight. Gusts should become less frequent overnight tonight. LLWS is possible this evening with SE winds 45-50 kt at 2kft, mainly east of NYC terminals. 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: Rain will be more intermittent before 1630Z. Visibilities at times will be a few miles higher than forecast. KLGA TAF Comments: Rain will be more intermittent before 1630Z. Visibilities at times will be a few miles higher than forecast. KEWR TAF Comments: Rain will be more intermittent before 1630Z. Visibilities at times will be a few miles higher than forecast. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Rain will be more intermittent before 1630Z. Visibilities at times will be a few miles higher than forecast. Fluctuation of MVFR/IFR ceilings before 1630Z. KHPN TAF Comments: IFR visibilities possible before 1730Z. KISP TAF Comments: IFR visibilities possible between 15 and 17Z. .OUTLOOK FOR 12Z WEDNESDAY THROUGH SATURDAY... .Wednesday-Wednesday Night...IFR in possible rain and fog. Potential for IFR/LIFR in fog Wednesday night. .Thursday...MVFR/IFR to start...with gradual improvement to VFR. .Friday...Chance of MVFR in showers/thunderstorms. .Saturday...VFR. && .MARINE...
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SCA conditions are expected today on all waters via a strong pressure gradient with ENE flow gusting to 25-30 kt. Gusts up to 25 kt remain possible on the Sound/Harbor/Bays through the first part of tonight, so SCA there is in effect until 06Z. Winds should diminish quickly late tonight into Wednesday, but ocean seas will remain elevated through Wednesday due to lingering swells, so SCA there remains in effect until 22Z Wed. A relatively relaxed pressure gradient over the region Wednesday night through Saturday will limit winds to 15 kt or less during this time frame. Sub-advy conditions are expected on the non- ocean waters Wednesday night through Saturday. Swells from the departing low will keep seas above SCA levels over at least part of the ocean waters from Wednesday night through Friday.
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&& .HYDROLOGY...
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Total rainfall of around 3/4 to 2 inches is expected through Wednesday. The highest amounts are most likely to occur across eastern Long Island, southern Connecticut, and interior northeast NJ. Some heavier showers have already moved across Long Island and will head up into southern CT this afternoon. Additional band of heavy rain possible late this afternoon and tonight. No significant (0.5 inches or more) widespread rainfall is forecast from Wednesday night through at least Sunday.
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&& .TIDES/COASTAL FLOODING...
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In response to a low pressure system moving northward along the eastern seaboard, minor coastal flooding is expected across the lower NY/NJ Harbor, the South Shore Bays of western Long Island including Queens and Brooklyn, and locations along the western Long Island Sound for the high tide this evening. Localized moderate coastal flooding is possible along the south shore bays of Nassau County. Only 1/2 to 1 foot of surge is needed to reach minor flood thresholds this evening, and strong easterly winds should pile water across these areas. A Coastal Flood Advisory is now in effect. Thereafter, minor coastal flooding thresholds will be approached in the same areas once again with the lower Wed Am high tide, and possibly briefly exceeded along the southern bays of Western Long Island. More widespread minor coastal flooding is possible with the higher Wednesday night high tide cycle, with minor inundation likely along the southern bays of LI. Only 1/3 to 3/4 of a foot of surge is needed to reach minor flood thresholds Wed night. In addition, the elevated water levels combined with a prolonged period of 5-9 ft breaking surf Today into Thu will result in beach erosion issues and may cause some localized dune toe erosion during the high tides tonight into Wed night.
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&& .OKX WATCHES/WARNINGS/ADVISORIES... CT...Coastal Flood Advisory from 10 PM this evening to 1 AM EDT Wednesday for CTZ009-010. NY...Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for NYZ074-075-178. Coastal Flood Advisory from 10 PM this evening to 1 AM EDT Wednesday for NYZ071-073-078-177. Coastal Flood Advisory from 6 PM to 11 PM EDT this evening for NYZ080-179. NJ...Coastal Flood Advisory from 6 PM to 10 PM EDT this evening for NJZ006-106-108. MARINE...Small Craft Advisory until 2 AM EDT Wednesday for ANZ330-335- 338-340-345. Small Craft Advisory until 6 PM EDT Wednesday for ANZ350-353- 355. && $$ SYNOPSIS...DS/DW NEAR TERM...Goodman/DS/DW SHORT TERM...DS LONG TERM...DW AVIATION...JM/PW MARINE...Goodman/DS/DW HYDROLOGY...DS/DW TIDES/COASTAL FLOODING...

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