Area Forecast Discussion
Issued by NWS Upton, NY

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528 FXUS61 KOKX 301540 AFDOKX Area Forecast Discussion National Weather Service New York NY 1140 AM EDT Sun Apr 30 2017 .SYNOPSIS... High pressure building into New England slowly moves east of the area through tonight. A warm front moves northward through the area tomorrow morning, followed by a cold front moving in from the west Monday night and passing through the area by Tuesday morning. High pressure builds in briefly for the middle of the week. An area of low pressure will bring unsettled weather for the end of the week into the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Warm advection coupled with instability above 850 mb has resulted in a few showers this morning across the Lower Hudson Valley. Will keep mention through early this afternoon until drier air aloft stabilizes the airmass. Isolated thunder is also a possibility. Anything that does develop should be brief. Temperatures have also been adjusted up several degrees based on latest obs/trends. This is due to the cold air filtering in slower behind the cold frontal passage this morning. Highs will be around 60 and should level off late this morning, if not begin to fall with the ongoing low-level cold advection. A surface high will continue to build into New England beneath a building upper high. Onshore flow gradually develops by afternoon, with a strengthening low-level inversion and increasing cloud cover through the day. Highs will be much cooler than yesterday, even a few degrees below climatological normals, follow this morning`s cold frontal passage and with the afternoon/evening onshore flow and cloud cover. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Continued onshore flow will lead to low-level saturation, with increasing chances for light drizzle through the evening and into Monday night, particularly as warm advection strengthens ahead of the returning/modified cold front. Low temperatures will be closer to climatological normals. The warm front is expected to move north of the area by morning/early afternoon with brief clearing possible behind the front. Meanwhile, the upper high off the southeast coast will gradually shift eastward ahead of a closed upper low. At this time, there is no clear signal for a pre- frontal trough, though there is a possibility of a convectively induced vorticity maximum moving through the area ahead of the main upper trough that may be sufficient enough to produce isolated afternoon thunderstorms, primarily north and west of the city. Afternoon highs largely depend on how quickly the warm front moves through and how much clearing can occur following its departure, though highs will likely be much warmer than Sunday. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... The cold front moves through from west to east Monday night, with rain and isolated thunderstorms clearing the area by Tuesday morning. Low temperatures will be mild amidst cloud cover and south flow, generally 5 to 10 degrees above climatological normals. Flow becomes more westerly following the frontal passage for Tuesday, and despite cold advection the westerly component will be favorable for downslope warming which may keep high temperatures a few degrees above guidance. Expect above normal highs for Tuesday. By Wednesday, a subtle upper trough and attendant cold front pass through the area by afternoon/evening, with a reinforcement of cold advection and temperatures closer to or slightly below normal. By late week, upper difluence ahead of a developing system across the central US will support moisture advection along the east coast and the intensification of a surface low across the Southeast that will gradually traverse northeastward into the region, leading to a period of unsettled weather into the weekend. && .AVIATION /16Z SUNDAY THROUGH THURSDAY/... High pressure centered off the New England coast and extending into the terminals will remain nearly stationary into this afternoon, then begin to drift offshore late this afternoon and tonight. A warm front will approach from the southwest tonight. VFR until around 23Z then MVFR conditions develop. IFR conditions are likely by late evening, 04Z, at all but KSWF and KGON, where they should develop after midnight. Airport minimums for ceiling and/or visibility could possibly be reached late tonight/early Monday morning. Winds continue to veer around to the E this morning, with speeds generally around 10 KT up to 13 KT. Winds veer to the E-ESE this afternoon. Occasional gusts 15 to 20 KT are possible late this morning and this afternoon. Winds become light and variable late tonight. .OUTLOOK FOR 12Z MONDAY THROUGH THURSDAY... .Monday...IFR or lower likely through morning, with a chance for improvement to MVFR or VFR in the afternoon. .Monday night...IFR or lower conditions, LLWS and scattered thunderstorms are possible. .Tuesday-Wednesday night...VFR. SW-WSW winds G15-20KT possible Tuesday. W-NW winds G15-25KT possible Wednesday/Wednesday night. .Thursday...MVFR or lower conditions developing is possible. && .MARINE... A moderate pressure gradient over the waters through Monday morning will result in winds of 15 to 20 KT. The pressure gradient increases Monday afternoon with gusts up to 25 KT. A persistent onshore flow will build seas to 5-6 ft over southern portions of the coastal ocean zones on Monday as well. The winds increase on Monday night, with solid Small Craft conditions on the coastal ocean waters. As a result, have issued an SCA for the coastal ocean waters for Monday and Monday night. On the non-ocean waters Monday night, gusts to small craft levels possible, but given limited mixing, confidence is not high enough to warrant headlines at this time. From Tuesday into Tuesday night, all waters likely will experience SCA conditions with gusts of 25-30 KT. The pressure gradient relaxes to light to moderate again by Wednesday, and remains so through Thursday, limiting winds to 15 kt or less. SCA level seas should linger on the coastal ocean waters into Wednesday, then possibly return again by late Thursday ahead of the next storm system. && .HYDROLOGY... No hydrologic impacts are expected through the forecast period. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 6 AM Monday to 6 AM EDT Tuesday for ANZ350-353-355. && $$ SYNOPSIS...MD NEAR TERM...MD/DW SHORT TERM...MD LONG TERM...MD AVIATION...Maloit/MET MARINE...Maloit/DW HYDROLOGY...MD

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