Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 160524 AFDOKX Area Forecast Discussion National Weather Service New York NY 1224 AM EST Mon Jan 16 2017 .SYNOPSIS... High pressure will build over the Tri-State Region overnight, and then to the south on Martin Luther King Day. A warm front approaches Tuesday and moves in Tuesday night. This moves across by early Wednesday with a cold frontal passage shortly thereafter. Weak high pressure returns for Thursday through Friday before it retreats north of the region next weekend. Another weak low pressure system approaches for the start of next weekend with possibly a stronger one approaching for late next Sunday. && .NEAR TERM /THROUGH TODAY/... Made minor changes this update to reflect the latest trends in observations and guidance. The forecast appears on track. With expectation of widespread sub-freezing temperatures, any residual moisture from melting snow earlier will refreeze so SPS issued for patchy black ice through 14z Monday. Deep layered ridging building in will produce dry weather and a mainly clear sky. There will be some cirrus at times, especially on Monday. Winds will be nearly calm overnight, and with some snow on the ground in places, the temperatures have been adjusted slightly below guidance. A blend of the guidance was used for Monday. && .SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/... Increasing theta-e could lead to some light precipitation late with an established warm air advection pattern. The 12Z ECMWF and GFS both produced something before 12Z, with the 18Z NAM trending in that direction. Low chances were therefore included in the forecast. Most of the area should be below freezing, so there will be some light icing if precipitation does in fact occur. It would be only an advisory level event if it did happen, so it has not been included in the Hazardous Weather Outlook per local policy. Because of the light southwest surface flow and increasing clouds, temperatures were forecast sightly higher than MOS, with a bias corrected all model blend used. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Main concerning item in the long term is the potential for freezing rain Tuesday. This will be mainly across the interior with otherwise a rain event Tuesday through Wednesday associated with a frontal system passage from the west. Bulk of the rain will be Tuesday afternoon through Tuesday night. Rain tapers to more of a mode of showers Wednesday afternoon and then tapers off altogether Wednesday night. The forcing for vertical motion will be enhanced from the approach of the left front quad of the upper level subtropical jet Tuesday afternoon through Tuesday night. The jet will be moving farther south of the region Wednesday through Wednesday night. The scenario will have a retreating high and antecedent winds will be the key because the winds become very light Tuesday, which will make it difficult to get warmth from onshore flow. The icing potential will be greater for the interior while the coast the time window will be quite brief in the morning. The warm front will be slow to move northeastward, not making it through the region until late Tuesday night into early Wednesday. An associated cold front follows shortly thereafter. The timing here will allow for warmer temperatures Tuesday night than during the day Tuesday and this will lead into Wednesday with a relatively warmer day as that persistent inversion aloft generally between 2kft and 7kft breaks down and there is more of westerly flow to mix down temperatures to the surface. This airmass building behind it is of Pacific NW origin so this will continue to allow for temperatures a small amount above normal. Weak high pressure returns Thursday through Friday and then this retreats to the north going into next weekend. Meanwhile, another weak low pressure system will be approaching for the start of the weekend along with a jet streak in the upper levels and another low pressure system approaching to close out next weekend. Overall, aside from the colder period to start Tuesday, temperatures in the long term are expected to be on average 5-10 degrees above normal, more so for Tuesday night and Wednesday. && .AVIATION /06Z MONDAY THROUGH FRIDAY/... High pressure builds over the area early this morning, then slides to the south into tonight. VFR through the TAF period. Light and variable winds (becoming at KHPN) into Monday morning. Winds increase to 6-10kt out of the WSW-SW late morning/early afternoon. Winds become light and variable again late afternoon/early evening. .OUTLOOK FOR 06Z TUESDAY THROUGH FRIDAY... .Late tonight...Low chance of MVFR. If precipitation occurs, freezing rain is possible, especially at interior terminals. .Tuesday...MVFR, then IFR conditions developing. Freezing rain likely Tuesday morning at interior terminals and possible at Long Island Terminals. Precipitation should become all rain throughout by early Tuesday afternoon. .Tuesday night-Wednesday...IFR or lower likely in rain. Conditions improving late Wednesday. SE winds G15-25KT possible Tuesday night at coastal terminals. NW winds gust 15-25KT possible Wednesday afternoon. .Wednesday night-Friday...VFR. && .MARINE... Forecast remains on track with light winds and seas generally 1-2 ft. Winds and seas will remain below Small Craft Advisory criteria through Monday night due to a relaxed pressure gradient over the area. The sub-SCA conditions will remain through early Wednesday with the pressure gradient remaining relatively weak. A SCA will be possible on the eastern ocean waters, mainly east of Moriches Inlet late Wednesday afternoon into Wednesday night as well as late Thursday through Friday. The late Thursday through Friday potential SCA would then be due to mainly higher seas potentially getting to 5 ft. Otherwise, below SCA conditions are expected for other waters and for other time periods during the marine long term (Tuesday through Friday). && .HYDROLOGY... Dry through at least Monday evening. Less than a tenth of an inch of precipitation is possible Monday night. About a half inch of rainfall is expected Tuesday through Wednesday with locally higher amounts possible. No hydrologic problems are expected. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...JMC/JM NEAR TERM...JMC/Maloit/JM SHORT TERM...JMC LONG TERM...JM AVIATION...Maloit/MET MARINE...JMC/Maloit/JM HYDROLOGY...JMC/JM is the U.S. government's official web portal to all federal, state and local government web resources and services.