Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 280056 AFDOKX Area Forecast Discussion National Weather Service New York NY 856 PM EDT Tue Sep 27 2016 .SYNOPSIS... A weakening cold front will remain offshore through Wednesday night while high pressure builds in from the Canadian Maritimes. A nearly stationary low pressure system over the Ohio Valley and Mid Atlantic regions, with an associated warm front remaining to our south due to strong high pressure over New England and the Canadian maritimes, will then bring an extended period of unsettled weather from Wednesday night into the weekend. The low will weaken and move slowly northeast early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Satellite shows low clouds across eastern Long Island, while radar shows isolated showers over the coastal waters, both associated with the offshore front. Bumped PoP up over eastern sections to account for these showers. Also bumped low temps down slightly elsewhere as these areas remain under mostly clear skies for a good portion of the night. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... The weather continues to become more unsettled during this timeframe. For Wednesday through Wednesday Night, the region will remain between a southward shifting large cutoff upper level low going towards the Tennessee Valley and the upper level shortwave in the Canadian Maritimes. There will be continued ridging between the two upper level features. However, at the surface, the center of high pressure remains strong and centered more towards Southeast Canada. There will be a low pressure area well southwest of the region that will be approaching. There is evident too from the model MSLP fields an inverted trough that will be approaching ahead of the surface low. Aloft, there will be increasing isentropic lift especially Wednesday afternoon through Wednesday night. This goes along with the SW flow in the mid to upper levels setting up warm air advection aloft. At the surface, a persistent pattern with high pressure in Southeast Canada and the local region being on the SW periphery of this high. This will give the region increasing NE flow and with the high being strong centered in the Canadian Maritimes, a steep pressure gradient will setup, resulting in winds becoming gusty. Model precipitation fields are showing some very light precipitation amounts across the region Wednesday and increasing towards the western portions of the region Wednesday night. This all conveys here a situation with moisture getting trapped under an inversion. This low level moisture will increase Wednesday and eventually materialize as drizzle or light rain to start with and a higher chance of rain Wednesday night when it will increase in intensity, coverage, and become more steady. At that time, the atmospheric column becomes more moist as well. Regarding temperatures Wednesday, used the ECS guidance and slightly adjusted downward. NE flow and increasing clouds points to a cooler than normal day on average out east while farther west highs are forecast to be near normal. Wednesday night features lows from a MAV/MET blend with again not much of a spatial range, mostly mid 50s to near 60 across the area. && .LONG TERM /THURSDAY THROUGH TUESDAY/... NWP guidance is in remarkably good agreement on the big picture through the weekend, with a large upper low completely cutting off from the westerlies and stalling over the Ohio Valley from Thu through Sat, then lifting across the Great Lakes on Sunday and weakening into an upper trough that slides across the Northeast on Monday. Meanwhile, as a strong upper high builds over the Western Atlantic, upper level confluence to its north where it meets the westerlies will maintain strong surface high pressure over northern New England and the Canadian Maritimes,that should nose down into our area and keep a warm front to our south. This combination will keep us in an unsettled weather pattern through at least the weekend, with periods of moderate to heavy rain. The first of these is likely to come Thu night into Fri morning via strengthening easterly low level Atlantic inflow, moistening mid levels via deep southerly flow aloft, a mid level vort max riding up the coast, and increasingly difluent flow aloft. Another bout of heavy rain may come to Long Island and southern CT on Saturday as another mid level impulse rides up the coast and as a weak wave of low pressure forms along the front just to the south. In between these bouts of heavier rain skies should remain overcast, with periods of intermittent light rain. An exception to this may take place Thu afternoon, when some guidance indicates the high may build down strongly enough from the north to shut off precip for a time across the interior. Some elevated instability will be present Sat into Sat night, with some rumbles of thunder possible. As the upper low lifts into the Great Lakes on Sunday, an associated weak triple-point low and/or occluded front should slowly lift across, with precip becoming more showery in nature. The upper low will continue to weaken and move east, but not clear our area until Tue morning, so forecast carries at least slight chance PoP until then. High temps in this regime will be slightly below average Thu-Fri, with a return to near average Sat into Mon, and then slightly below average on Tue as Canadian high pressure starts to return. Low temps meanwhile should be mostly warmer than average until Mon night. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Forecast transitions over to a prolonged period of sub-VFR conditions starting on Wednesday and likely persisting into the first half of the weekend. High pressure builds south from eastern Canada and noses into the area late tonight into Wednesday. At the same time, low pressure will drop south across the Great Lakes and into the Ohio Valley states. This will result in a strengthening NE flow with overrunning clouds and possible light rain. Widespread MVFR conditions are forecast to develop from east to west, as early as 09Z at KGON, and as late as 16Z across the Lower Hudson Valley. There is the possibility for these ceilings to move in earlier than forecast, as well as drop into the IFR category, especially for the coastal terminals. Light rain is a possibility, but not expecting restrictions to visibility at this time. Another potential wrinkle in the forecast is the magnitude of the high building in from the north. Should the high build a bit farther south, this could improve conditions for a time. Light and variable winds this evening becoming NE around 10 kt early Wednesday morning. By mid to late morning, NE winds increase to 10-15 kt and become gusty at times, as high as 20-25 kt at the coast. ...NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: Amendments likely for ceiling category, especially during Wednesday morning. KLGA TAF Comments: Amendments likely for ceiling category, especially during Wednesday morning. KEWR TAF Comments: Amendments likely for ceiling category, especially during Wednesday morning. KTEB TAF Comments: Amendments likely for ceiling category, especially during Wednesday morning. KHPN TAF Comments: Amendments likely for ceiling category, especially during Wednesday morning. KISP TAF Comments: Amendments likely for ceiling category, especially during Wednesday morning. .Outlook for 18Z Wednesday through Saturday... .WED NIGHT...Widespread MVFR ceilings, possibly IFR. NE winds G20-25KT at the coastal terminals. .THU-SAT...IFR/MVFR in showers. NE winds 15-20 kt with gusts 25-30 kt possible THU-FRI. .SUN...Mainly VFR but MVFR possible with a chance of showers. N winds 10-20 kt. && .MARINE... Latest obs still show 5-ft seas at 44017 and 6-ft seas at 44097, the combination of 2-ft wind waves and 3-4 ft southerly swell. Combined seas may come down a little overnight, but decided to start SCA for the eastern ocean waters now rather than wait until daytime Wed. Then Wednesday into Wednesday Night, SCA looks more probable across all waters especially on the ocean. There will be a tight pressure gradient setting up between a Southeast Canada high and low pressure southwest of the region. Think max gusts reach near 30 kt, mostly Wednesday night. Then as the pressure gradient tightens further, easterly gales appear likely from Thu into Fri morning mainly on the ocean, but perhaps also on the nearby bays of eastern Long Island and eastern Long Island Sound, with SCA conds on the harbor and western Sound. Issued gale watch for the ocean for Thu into Thu night. SCA conds are likely to continue thereafter on all waters into Fri, on the eastern Sound/bays into Fri night, and on the ocean into Sat. && .HYDROLOGY... Any rain Wednesday through Wednesday night will be light, with rainfall totals less than 1/4 inch. The heaviest rainfall amounts with a nearby low pressure system should fall to our west, but there could still be some periods of heavier rain Thu night into Fri morning, also Fri night into Saturday. Total basin average rainfall from Thu through Sat should range from 1 to 2 inches, highest east, with potential for local amounts of 2-3 inches across parts of Long Island and southern CT. This is not expected to cause major hydrologic impacts. && .TIDES/COASTAL FLOODING... A persistent moderate easterly flow during mid to late week may combine with increasing astronomical high tides associated with the new moon on Friday to cause minor to locally moderate coastal flooding. The high tide cycles from Thu night into Fri morning appear to be of most concern. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from noon Wednesday to 6 AM EDT Thursday for ANZ330-335-338-340-345. Gale Watch from Thursday morning through late Thursday night for ANZ350-353-355. Small Craft Advisory from 10 AM Wednesday to 6 AM EDT Thursday for ANZ350-353-355. && $$ SYNOPSIS...Goodman/JM NEAR TERM...Goodman/JM SHORT TERM...JM LONG TERM...Goodman AVIATION...DW MARINE...Goodman/JM HYDROLOGY...Goodman/JM TIDES/COASTAL FLOODING... is the U.S. government's official web portal to all federal, state and local government web resources and services.