Area Forecast Discussion
Issued by NWS Upton, NY

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618 FXUS61 KOKX 222335 AFDOKX Area Forecast Discussion National Weather Service New York NY 735 PM EDT Sat Apr 22 2017 .SYNOPSIS... As a weak wave of low pressure departs this evening, high pressure will then slowly build into the region from the west tonight, across the area on Sunday, then moves offshore on Monday. A wave of low pressure over the Southeast states on Monday, will track slowly up the eastern seaboard through midweek. High pressure will build back in for the end of the week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Shearing northern stream shortwave energy slides through the region tonight and to the south Sunday morning...with high pressure building in from the NW. Gradual drying and clearing expected from NW to SE overnight. Back edge of pcpn currently in ern PA...should move E of NYC by 01z or so and out of the area completely by 03z. Northern half of the CWA may only see some sprinkles with light rain in NYC and Long Island. Adjusted pops to reflect this thinking. Otherwise...minor adjustments to temps and dews to better reflect current conds and trends. Lows near seasonable...with lows in the 40s most places...except upper 30s across far outlying areas. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Region will lie in a near zonal upper flow between a polar upper low over interior Ontario/Quebec and a closed upper low moving trough the deep south. At the surface...high pressure builds into the region Sunday morning and then east Sun afternoon into Sunday night. Mostly sunny conditions on Sunday with sunshine likely filtered by jet cirrus. Light NE flow in the morning expected to give way to afternoon return flow and coastal sea breezes. Highs should be near seasonable...lower 60s coast...mid to upper 60s NYC/NJ metro and upper 60s to around 70 interior. Tranquil conditions Sunday night...with increasing mid-deck late ahead of a slowly approaching low pressure system from the south. Lows nears seasonable...upper 30s across far outlying areas and 40s elsewhere. && .LONG TERM /MONDAY THROUGH SATURDAY/... NWP is in good agreement with the H5 pattern through much of the upcoming week...with timing and amplitude differences at the end of the week and into next weekend. A split flow over the Eastern US starts the period with a cutoff low pres system over the SE states with ridging to the N and E. The ridge over the Atlantic will amplify as the week progresses...creating a blocking pattern and forcing the low up the eastern seaboard. While it is quite certain that the local area will be impacted by this storm...the details remain uncertain...the NAM/GEM in one camp keeping the system over land and tracking it over or near NYC Tue night/Wed morning...and the GFS/EC tracking it just S and E of Montauk. These differences will hopefully be resolved in the next few model runs as it will impact where the inverted sfc trough develops with the axis of heaviest rain. Due deep layered ridging ahead of the storm...have slowed up timing of pops...and have kept Monday mostly dry with better chances Monday night as subsidence weakens. Winds will also increase and become gusty Mon night and Tue. 30-40 kt LLJ lifts through Tue aftn/eve...but a low level inversion should keep most of these winds aloft. These stronger winds will also depend on where the low tracks. If the low tracks over NYC the higher winds will remain to the east. The forward progression of the system is also uncertain...and current forecast may be too quick decreasing pops to chc Wed morning. System departs Wed night with ridging aloft developing over the east and a broad trough out west. This will lead to warming temps through the remainder of the week. A cold front moves towards the area on Thu...but most guidance has showers/tstms mostly dissipating before it reaches the region. This front is then forecast to stall near the area into next weekend with potential waves of low pressure keeping it unsettled. As for temperatures, near seasonable levels through mid week, if not a bit cooler during the daytime due to cloud cover and rain. A significant warmup is possible for the end of the week with rising heights aloft. && .AVIATION /23Z SATURDAY THROUGH THURSDAY/... High pressure will build in from the west tonight and pass Sunday. Initial MVFR cigs possible before 3Z, especially near the coast, then VFR with clearing. Light winds turn to the N later this evening and overnight, 10 kt or less. Light winds Sunday morning turn to the S/SE by afternoon. .OUTLOOK FOR 00z MONDAY THROUGH THURSDAY... .Sunday night ...VFR. .Monday...VFR during the day. Chance MVFR in rain at night. .Tuesday...Chance IFR in rain. NE gusts 20-25 KT near coast possible. .Wednesday...MVFR possible early, becoming VFR. .Thursday...VFR. && .MARINE... 4-5 ft E swells on the ocean should gradually subside overnight into Sunday...which should keep seas just below SCA levels. 5 ft seas may briefly re-develop on the ocean waters tonight as NW winds increase to 15 kt...but should be short- lived. Winds and seas should run below SCA levels Sunday into Monday as high pressure builds from the north tonight into Sunday night. The high weakens Monday as low pressure moves off the southeastern coast begins to track slowly to the north. The low pressure system over the SE states Monday will track slowly N-NE through midweek. A prolonged and increasing easterly flow will set up from Monday night into Wednesday. Winds and seas are expected to build to SCA levels Mon eve with the potential for gale force winds Mon night into Tue. Winds diminish Tue night...but seas on the ocean will be slow to subside and possibly linger into Thu. && .HYDROLOGY... An additional tenth of an inch of rainfall is possible into this evening, mainly from portions of northeastern New Jersey, across New York City, and Long Island. Lower amounts to the north. Between 1/2 and 1 1/2 inches of rainfall is possible late Monday into Wednesday depending on the track of low pres. No hydrologic impacts are anticipated at this time. && .TIDES/COASTAL FLOODING... Potential for minor coastal flooding for vulnerable coastal communities with the Tue high tide cycles due to a potential coastal storm working up the coast. The evening cycle may have the higher threat as only 1/2 to 1 ft of surge is needed to reach minor flood thresholds. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.