Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 160834 AFDOKX Area Forecast Discussion National Weather Service New York NY 434 AM EDT Mon Apr 16 2018 .SYNOPSIS... Low pressure passes through today with high pressure building in very slowly behind it through Wednesday as the storm heads into southeastern Canada. A weak low pressure system then affects the area Thursday into Friday. High pressure builds into the region for next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Low pressure passes over or just north of the NW zones today. This will help push a warm front through at least part of the tri-state area today, followed by a cold or occluded front this afternoon. Showers have already developed ahead of the warm front with strong isentropic lift. A line of showers with locally heavy downpours and perhaps a rumble of thunder will then push in ahead of the cold front during the morning commute for the city and surrounding areas, then exit eastern LI early this afternoon. A secondary line may also form and push through a good portion of the tri-state area this afternoon. Line(s) of heaviest downpours could become less organized by the time they reach here, but nevertheless deep moisture and strong lift should produce some heavy downpours over the area. Based on flash flood guidance and anticipated rainfall, the Flash Flood Watch remains unchanged. See the hydrology section for more information. Ahead of the cold front, 950mb winds near 70-75 kt pass through the coastal areas. A strong inversion should prevent the likelihood of severe-level wind gusts reaching the surface, but near-severe gusts cannot be ruled out in/near any heavy downpours - even away from the coast. Not enough confidence for widespread gusts up to wind advisory levels to issue any advisories at this time. Thinking is that such gusts will be more isolated in nature. Sustained winds could come close to reaching criteria at the coast this morning, but again, not high enough of a chance with widespread coverage to go with an advisory. In spite of the rain and clouds, it appears that high temperatures will end up near normal. && .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/... High pressure slowly builds in at the surface, however cyclonic flow aloft continues with an upper low passing to the north. Low chances of showers this evening for most spots, then thermal profiles cool off enough again for a chance of mixed rain and snow showers NW of the city late tonight into early Tuesday morning. For the rest of Tuesday, low chances for showers across most of the region along with high temperatures below normal. Wednesday should be rain-free with a flatter flow aloft, and should feature more in the way of sunshine and highs closer to normal. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Models are in better agreement on a complex upper level pattern for the mid to late week, with shortwave energy riding over Central US/Canada ridge and then partially phasing with SE Canada closed low Wed Night into Thu. This new closed low then interacts with the progressive closed low, now entering the PAC NW, racing eastward across the CONUS the first half of the week. There is still some spread in the timing/magnitude of interaction of these two closed lows, but general consensus is for the PAC energy to rotate around the digging Canadian upper low, sending a resultant low pressure system through the region Thu into Thu Night. The nature of this evolution will determine whether the primary low remains dominant and tracks over or just north of the region, or a secondary low develops along the coast and tracks over or just south of the region. At this time, there does not appear to be enough phasing for a strong coastal storm with heavy precip and wind, but a southern track could introduce some wintry precip across at least the interior. This energy and system should move east Friday into Friday Night, with mean troughing lingering through the weekend. At the surface, Canadian high pressure should building into the region, with dry conditions and temps moderating towards seasonable. && .AVIATION /09Z MONDAY THROUGH FRIDAY/...
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Strong high pressure builds down from southeastern Canada into the morning, as a warm front slowly approaches from the south. The warm front may partially lift through the area during the day today, followed by a cold front this evening. Occasional showers with brief heavy downpours will continue through the early morning, with a more significant line of heavy showers and potentially isolated thunderstorms expected to move through from W to E 12-16Z. MVFR to IFR conditions will prevail, with IFR more likely in the development of heavy rainfall. VFR conditions return from W to E by late afternoon/evening following the cold frontal passage. Timing of these features may be +/- 1-2 hours of forecast. The bigger challenge is the winds. Highest winds should coincide with the band of heavy rain moving through this morning. Other concern is whether a wave of low pres riding along the cold front is able to pull the warm front partially through the area, mainly LI/NYC terminals, before the cold front moves through. Wind direction forecast would be impacted by this. Winds shift to the west late aftn/eve and decrease fairly rapidly. LLWS confined to the 12-18z period at all terminals. 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: IFR CIGS may be occasional through 11Z. Winds may briefly gust to around 40 kt in vicinity of heavier showers. Isolated thunder possible 11-16Z with heaviest rainfall. The afternoon KJFK haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KLGA TAF Comments: Winds may briefly gust to around 40 kt in vicinity of heavier showers. Isolated thunder possible 11-16Z with heaviest rainfall. The afternoon KLGA haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KEWR TAF Comments: Winds may briefly gust to around 40 kt in vicinity of heavier showers. Isolated thunder possible 10-15Z with heaviest rainfall. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Winds may briefly gust to around 40 kt in vicinity of heavier showers. Isolated thunder possible 10-15Z with heaviest rainfall. KHPN TAF Comments: Winds may briefly gust to around 40 kt in vicinity of heavier showers.Isolated thunder possible 11-16Z with heaviest rainfall. KISP TAF Comments: Winds may briefly gust to around 40 kt in vicinity of heavier showers. Isolated thunder possible 12-17Z with heaviest rainfall. .OUTLOOK FOR 12Z TUESDAY THROUGH FRIDAY... .Tuesday-Wednesday...VFR. SW-NW winds G15-25KT possible. .Wednesday night-Thursday...MVFR or lower possible in any rain. W winds G15-20KT possible Thursday. .Thursday night-Friday...MVFR or lower possible in mainly rain with a wintry mix possible to the NW of city terminals late Thursday night/Friday morning. W-NW winds G15-25KT possible.
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&& .MARINE... Low pressure with a strong low level jet shifts through the waters today. With a strong inversion in place, it will be difficult for storm force winds to mix down to the surface. Will therefore maintain a gale warning for all waters. Extended the warning in time for the non-ocean waters to account for the possible verification of the slower guidance regarding the timing of when the strongest pressure gradient and low level jet shifts east of the waters. Winds diminish tonight, but still at advisory levels in the evening. Ocean seas will remain elevated with a lingering swell. SCA conds then expected for Tuesday on the ocean with a gusty west wind and seas above advisory criteria. It might not be until late Wednesday night before all ocean waters subside below advisory levels. A light to moderate pressure gradient over the waters Thursday- Friday night should limit winds to 15 kt or less. However, seas on the coastal ocean waters could reach SCA levels Thursday and Thursday night and possibly linger into Friday. && .HYDROLOGY... An additional 1-2 inches of rainfall is expected today. Not anticipate widespread river flooding, especially forecast points, except minor to possibly moderate flooding for the flashier rivers and streams in NJ and Rockland county, Orange county. Urban/poor drainage flooding is likely, with low confidence in issuing flash flood warnings for NYC and locations east of the Hudson (LI, Srn CT, Westchester, Putnam.) The most susceptible areas for flooding remain across NE NJ, and the lower Hudson Valley west of the Hudson river. An expected band/line of heavy showers this morning would be the main culprit for flooding. A secondary line this afternoon is not out of the question either. Timing of the Watch remains through 6 pm Monday. No hydrologic impacts are expected Tue through Sun. && .TIDES/COASTAL FLOODING... Widespread minor to localized moderate coastal flood impacts are expected along lower NY/NJ Harbor, Jamaica Bay, the South shore bays of western Long Island, and western LI sound during the times of high tide this morning/early afternoon due to an easterly gale flow. Tidal departures of 1-2 ft are needed for minor flooding, with 2 to 3 ft for moderate. Brief and localized minor impacts are possible along vulnerable coastal locales of Eastern LI and SE CT, with this morning`s high tides. Along the Atlantic ocean beachfront, 5 to 8 ft breaking waves and elevated water levels will result in widespread beach flooding and erosion, with minor dune erosion possible. While along Western Long Island Sound shorefront, 3 to 5 foot breaking waves may result in locally moderate coastal flooding with minor damage possible to shoreline structures. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Coastal Flood Advisory until 2 PM EDT this afternoon for CTZ009-010. NY...Flash Flood Watch through this afternoon for NYZ067-069. Coastal Flood Advisory until 1 PM EDT this afternoon for NYZ072-074-075-080-178-179. Coastal Flood Advisory until 2 PM EDT this afternoon for NYZ071-073-078-176-177. NJ...Flash Flood Watch through this afternoon for NJZ002-004-006- 103>108. Coastal Flood Advisory until 1 PM EDT this afternoon for NJZ006-106-108. MARINE...Gale Warning until 6 PM EDT this evening for ANZ330-340-345- 350-353-355. Gale Warning until 2 PM EDT this afternoon for ANZ335-338. && $$ SYNOPSIS...JC NEAR TERM...JC SHORT TERM...JC LONG TERM...NV AVIATION...MD MARINE...JC/NV HYDROLOGY...JC TIDES/COASTAL FLOODING... EQUIPMENT...

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