Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 250822 AFDOKX Area Forecast Discussion National Weather Service New York NY 422 AM EDT Tue Apr 25 2017 .SYNOPSIS...
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Low pressure slowly tracks up along the eastern seaboard through Wednesday night. Weakening low pressure along the New England coast Wednesday night tracks northeast and up into the Canadian Maritimes by the end of the week. A weakening frontal boundary dissipates across the area on Friday, followed by another weak frontal boundary moving into the area Saturday into Saturday night. The latter of which stalls out nearby into 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. Dry low levels have prevented widespread rain from occurring this morning as radar returns remain on the light side and just a few hundredths reported where light rain has fallen. Higher returns appear to remain offshore to our south and east. The NAM-12km, NAM- 3km, and the HRRR show a brief lull in the precipitation after day break as dry air continues to battle weak lift and a slow moistening trend. This will likely be short- lived as stronger isentropic lift and deeper moisture work up the east coast ahead of the low late this morning and into the afternoon. Latest thinking is for mainly light rain this morning with potential for a brief lull, then steadier rain moves in from south to north this afternoon. Fairly strong pressure gradient between the approaching low and high to the north brings 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. Precipitable waters increase 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 airmass, slow moving stacked low, and low level jet 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 shifts to the east after 06z, which will focus the heaviest rain across eastern Long Island and southern Connecticut. Some hints at weak elevated instability on BUFKIT soundings, but have left thunder out of the forecast for now. Better instability still looks to remain to the south and east. 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 further west as well. The close proximity of the stacked low should keep low clouds 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/...
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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.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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Low pressure slowly moves up the Mid-Atlantic coastline today and tonight. MVFR and IFR cigs expected to gradually develop and prevail in bands of light rain early this morning. Visibility will take some time to lower, possibly late morning or afternoon. Expecting IFR/LIFR ceilings this afternoon as rain becomes steadier and moderate to heavy. The low conditions continue early tonight. E/NE winds increase this morning, with speeds 15-25 kt and gusts 25-30 kt after 12-14Z. Highest sustained winds for coastal terminals. Winds diminish somewhat tonight. LLWS possible this evening with SE winds 45-50 kt at 2kft. ...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: Forecast timing of onset for IFR ceilings may this morning be off an hour or two. Steadier rain this afternoon. KLGA TAF Comments: Forecast timing of onset for IFR ceilings may this morning be off an hour or two. Steadier rain this afternoon. KEWR TAF Comments: Forecast timing of onset for IFR ceilings may this morning be off an hour or two. Steadier rain this afternoon. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Forecast timing of onset for IFR ceilings may this morning be off an hour or two. Steadier rain this afternoon. KHPN TAF Comments: Forecast timing of onset for IFR ceilings may this morning be off an hour or two. Steadier rain this afternoon. KISP TAF Comments: Forecast timing of onset for IFR ceilings may this morning be off an hour or two. Steadier rain this afternoon. .OUTLOOK FOR 06Z WEDNESDAY THROUGH SATURDAY... .Late tonight...IFR/LIFR in rain. NE gusts 20 to 25 KT. Winds diminish further. .Wednesday-Wednesday Night...IFR in rain. 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.
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&& .MARINE...
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SCA conditions are expected today on all waters with a strong pressure gradient. Gusts up to 25 kt remain possible on LI Sound, LI Bays, and NY Harbor through the first part of tonight. Have therefore extended the SCA on these near shore waters until 06z. Winds diminish quickly on the ocean late tonight into Wednesday as the low pressure moves of the waters. However, ocean seas will remain elevated through Wednesday due to lingering swells so have extended the SCA until 22z Wednesday. 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-small craft conditions are expected on the non-ocean waters as a result Wednesday night through Saturday. On the coastal ocean waters, swells from the departing coastal low will keep seas above SCA levels over at least part of each coastal water zone Wednesday night through Friday. Seas should fall below 5 ft on all coastal ocean zones by Saturday.
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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 Long Island and southern Connecticut where the best chances of minor flooding of poor drainage and low lying areas will be. The heaviest rainfall occurs 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 to 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...
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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.
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&& $$ SYNOPSIS...DS/DW NEAR TERM...DS SHORT TERM...DS LONG TERM...DW AVIATION...PW MARINE...DS/DW HYDROLOGY...DS/DW TIDES/COASTAL FLOODING...

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