Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 271906 AFDOKX Area Forecast Discussion National Weather Service New York NY 306 PM EDT Tue Sep 27 2016 .SYNOPSIS...
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A weakening cold front offshore going into tonight will slowly move farther offshore. This boundary remains southeast of Long Island during Wednesday and Wednesday night while weak high pressure builds in from the Canadian Maritimes. However there will be an approaching area of low pressure along with a warm front by Wednesday night. This low pressure over the Ohio Valley and Mid Atlantic states will meander about this region into the weekend bringing an extended period of unsettled weather. The low will gradually lift through New England early next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Any showers remain southeast of Long Island with the weakening cold front and will diminish altogether by late this afternoon. The front further weakens this afternoon as it remains southeast of Long Island. Winds at the surface will be light out of a general southwest direction. The forecast is generally on track this afternoon with dry conditions still anticipated. Clouds are thinning out from NW to SE going into the afternoon as drier air works in with the more westerly flow. High temperatures will be near normal but perhaps slightly above normal for the western half of the CWA with more sun. There is a moderate risk of rip current development at the ocean beaches for today.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
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The weather will become more unsettled during this timeframe. Starting aloft with tonight, there will be some ridging taking place across the region. This will allow for subsidence. The local region will actually be between a large cutoff upper level low in the Ohio Valley and an elongating upper level trough in the Canadian Maritimes as it becomes more of an open wave. At the surface, the front will further weaken and move farther offshore as high pressure builds into the Canadian Maritimes. Mainly dry conditions should prevail but there could be a few showers southeast of Long Island, closer to the lingering frontal boundary. Lows were taken from the ECS guidance which was relatively warmer and exhibited less spatial range between temperatures. 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 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.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... NWP guidance and ensembles are in good agreement with the overall H5 pattern across North America through the first half of the weekend...then solutions begin to diverge with the next trough/cutoff low entering the PacNW although this should not impact the local area until early next week. The long term period starts with cutoff low pres over the Ohio Valley trapped between ridging to the east and west. This will result in the system meandering about this area into the weekend before the ridge to the east finally begins to break down allowing it to track through the eastern Great Lakes and New England early next week. Confidence decreases in the finer details...although a frontal boundary extending from the sfc low in combination with strengthening isentropic lift will result in much needed overrunning rainfall Wed night into Fri morning. While the periods of heavier rainfall remain uncertain there is a signal that Thu night could be one timeframe where heavier pcpn does occur with mid level vort energy passing through. Unsettled pattern will continue into the weekend with abundant cloud cover and perhaps a transition to more showery pcpn with mid level ridging trying to build in from the east. Moisture transport will still be originating from the Gulf of Mexico under this pattern. Warm front may push through on Sun as the system begins to lift through the Great Lakes. This will also push the heaviest rainfall to the north as well...resulting in decreasing PoPs through Mon. The EC remains the western outlier...hanging tough with this soln for the past 3 runs...although it has moved somewhat closer to consensus. Based on the location of the system...heaviest rainfall is expected to fall west of the area. See hydro section for more information on expected totals locally. Removed thunder as the lower heights associated with the deep low are too far west...thus it remains too warm aloft for any elevated instability. && .AVIATION /19Z TUESDAY THROUGH SUNDAY/... VFR at most terminals but pockets of MVFR remain especially KISP and KGON. Little change is expected the remainder of this afternoon but continued improvement expected from west to east. Light wind mainly W 10 kt or less this afternoon may briefly become S-SW around city terminals. Winds become light and variable this evening before becoming NE around 5 kt early Wednesday morning. By midday...ne winds increase to near 15 kt and become gusty at times near 20-25 kt. ...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 to adjust wind direction and/or cigs. KLGA TAF Comments: Amendments possible to adjust wind direction and/or cigs. KEWR TAF Comments: Amendments possible to adjust wind direction and/or cigs. KTEB TAF Comments: Amendments possible to adjust wind direction and/or cigs. KHPN TAF Comments: Amendments possible to adjust wind direction and/or cigs. KISP TAF Comments: Amendments possible to adjust wind direction and/or cigs. .Outlook for 18Z Wednesday through Saturday... .WED...Becoming MVFR late morning/early afternoon. NE gusts to 25 kt possible in the afternoon. .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...
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Sub SCA initially but with a weak wind field, there will not be much to resist incoming swells from the south. Thinking there will be some higher seas eventually getting back into the ocean zones that may meet SCA criteria tonight with otherwise sub SCA conditions across all other waters. Then Wednesday into Wednesday Night, SCA looks more probable across all waters with ocean having a higher probability of both winds and seas getting to SCA levels. There will be a tight pressure gradient setting up between a Southeast Canada high and low pressure southwest of the region. The rough conditions continue into at least Thu night due to a tight pres gradient across the waters. There still remains a low probability of marginal gale force gusts during this time...thus will continue the mention in the HWO. It may only be confined to the ocean waters however. The GFS is indicating gusts into the 40`s but feel this is overdone. NAM looks more reasonable...but perhaps a tad light. Have used a compromise of the 2 weighted more towards the NAM. Winds subside on Fri as the gradient weakens...although seas on the ocean will remain elevated...possibly into Sat.
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&& .HYDROLOGY...
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Dry weather expected through tonight and any rain Wednesday through Wednesday night will be light with rainfall totals less than a quarter of an inch. The proximity of a low pressure system late in the week looks to be too far west at the current time for the local area to fall in the axis of heaviest QPF. Currently between 1/2 and 1 1/2 inches of rainfall is forecast between Wed night through Sat. This is not expected to cause any hydrologic impacts.
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&& .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 late this week. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...None.
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&& $$ SYNOPSIS...24/JM NEAR TERM...JM SHORT TERM...JM LONG TERM...24 AVIATION...IRD MARINE...24/JM HYDROLOGY...24/JM TIDES/COASTAL FLOODING...

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