Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 200534 AFDOKX Area Forecast Discussion National Weather Service New York NY 1234 AM EST Fri Jan 20 2017 .SYNOPSIS... Weak high pressure remains over the region tonight. An upper level disturbance will approach from the south on Friday, and weaken as it moves across Friday night. High pressure briefly returns on Saturday. Deepening low pressure moving across the southern states on Sunday will reach the southern Mid Atlantic region by Monday morning, while high pressure builds southeast into the Canadian Maritimes. The low will intensify into a significant coastal storm as it moves up the coast toward the area Monday through Tuesday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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Surface observations and satellite data continue to show extensive cloud cover. Over the last few hours, stratus has filled back in where it had scattered out earlier this evening. Will continue with a mostly cloudy to overcast sky forecast. Have raised min temperatures several degrees as clouds have kept temperatures relatively stable. Some breaks in the clouds are possible towards day break and could outlying areas drop several degrees. Forecast low temperatures now range from the lower 30s inland to the middle and upper 30s near the coast.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... High pressure ridge slides east early Friday morning, allowing the next wave of low pressure to approach from the southwest. Clouds increase Friday morning. As the wave nears the region, POPs will gradually increase through the afternoon and evening. All the forecast models are hinting at some kind of light to moderate precipitation, so will continue to mention likely POPs. QPF amounts will remain fairly light, with less than a quarter of an inch of rainfall expected. The highest amounts are expected to fall west of NYC. POPs gradually diminish after midnight as the wave weakens and lifts north. High temperatures on Friday continue about 5 degrees above normal in the lower and middle 40s. Friday night, lows fall into the 30s. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... A shearing shortwave will move ne of the region Sat with ridging moving in at the surface and aloft. Weakening shower activity should be pushing east Sat morning...but lingering cloud cover is likely with weak waa under subsidence inversion. Temps likely run well above seasonable in the upper 40s to lower 50s...with potential for mid to upper 50s for NE NJ/NYC metro with breaks of sunshine. Main focus is on a storm forecast to take shape as strong Pacific jet energy crashes onshore the California coast Fri/Sat...allowing an upper level system to close off over the southern plains this weekend and then negatively tilt up the east coast Monday into Tuesday. The result will be strong low pressure tracking through the southern states this weekend...and then tracking up the eastern seaboard towards the area Mon/Tue. Models in general agreement with the synoptic fields...but spread exists in timing/intensity of the closed upper low as it move up the coast...which is playing out in model spread on track/speed of the surface low Mon/Tue. SBU ensemble sensitivity points towards a strong wave packet emanating from shortwave energy developing off the eastern Asia coast as the determining factor. Have stayed close to ensemble means with forecast...with general trends of low pressure tracking a bit farther se and slower than 24 hours ago. Potential exists for multiple impacts including strong winds, heavy rain (wintry mix NW) and minor to locally moderate coastal flooding, with likelihood of occurrence in that general order. In terms of heavy precip...PWATs of 3-4 stds above normal are being signaled as the system taps into tropical connection to the Caribbean and Eastern Pacific. The potential for 1 to 3 inches of qpf with higher amounts continues. Based on strong dynamics and se trend towards a track over or just se of LI...potential for thermal profiles to diabatically cool to near freezing and result in a rain/snow mix well N&W of NYC for a portion of this event...with even a period heavy wet snow across NW hills. Still too much uncertainty at this point to talk amounts...but at least a low potential exists for an accumulating wet snow for the NW hills. In terms of winds...GEFS signaling an easterly llj 4-5 std above normal. EPS probabilities for wind gusts over 50 kt continue to run in the likely range Mon/Mon night for the immediate coastline, and the extended 00z/12Z GFS/ECMWF MOS guidance indicate sustained winds 25-30 kt along the coast and in the higher interior elevations. This signals moderate potential for wind advisory conditions for the coastal and low potential for high wind. See coastal flood sections for potential coastal flood impacts. Gradually improving conditions Tue aft into Tue night as the upper low pivots ne and low pressure tracks up the New England coast. && .AVIATION /05Z FRIDAY THROUGH TUESDAY/...
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High pressure builds in from the west overnight and then moves offshore on Friday as a warm front approaches from the south. Ceilings at or below 3 kft much of the time overnight into early Friday morning. VFR conditions will return briefly for the mid to late morning on Friday before MVFR conditions return late Friday afternoon and early Friday evening with light rain likely. N-NE winds dropping off overnight to near 5 kt or less. A return E flow develops late Friday morning at less than 10 kt. The winds then veer to the SE by the late afternoon and will remain under 10kt. .OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY... .Friday night... MVFR and IFR in -RA, with a period of LIFR possible at some terminals mainly after 3z. .Saturday-Saturday night...MVFR or lower possible early Saturday morning, followed by VFR for the late morning and into Saturday afternoon and night. .Sunday-Sunday night...MVFR or lower in -RA, mainly late Sunday afternoon through Sunday night. Moderate rain develops at night. NE gusts 20-25 kt by late Sunday afternoon and evening. NE gusts 30-40 kt Sunday night. .Monday...IFR with moderate to heavy rain and strong E-NE winds. NE gusts 35-45 kt. .Tuesday...Rain tapering off with improving ceilings. Gusty NW winds possible later in the day.
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&& .MARINE...
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Easterly swell has slowly subsided, but sill seeing significant wave heights at 44025 close to 6 ft. Since the other buoys are still close to 5 ft, will continue with the Small Craft Advisory for Hazardous Seas. Winds and seas should then remain below SCA levels on all waters through Friday night. An intensifying storm moving up the coast early next week will likely bring easterly gales to all waters from Sunday night into Monday night...with storm force wind gusts may be possible on the ocean and eastern most Long Island Sound. If these winds come to fruition...15 to 20 ft waves possible over the ocean waters...with 4 to 8 ft on LI sound.
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&& .HYDROLOGY... No significant precipitation is expected through Saturday night. Potential for significant rainfall of 1 to 3 inches, with locally higher amounts with a coastal storm early next week. If high end rainfall amounts are realized...this will present a threat for minor areal flooding...including small stream flooding. Rises on larger rivers would be likely...but at this point the potential for minor flooding appears slight. && .TIDES/COASTAL FLOODING... A strong coastal storm may cause minor to locally moderate coastal flooding if its highest surge coincides with the early morning high tide cycles either Mon or Tue, which is the higher of the two daily high tide cycles. Stevens ensemble guidance is showing potential for surge building to 3 to 4 ft on Monday. Surge needed to cause minor coastal flooding is about 1.5-2.5 ft on the Long Island South Shore back bays, and 2.5-3.0 ft elsewhere. Surge needed to cause moderate coastal flooding is about 2.5-3.0 ft on the Long Island South Shore back bays, and 3-4 ft elsewhere. The other concern will be for significant beach erosion from long period easterly swells of 10-15+ ft Mon into Tue. Localized washover cant be ruled out if higher surge values are realized. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory for hazardous seas until 6 AM EST early this morning for ANZ350-353-355.
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&& $$ SYNOPSIS...BC/NV NEAR TERM...JMC/DS SHORT TERM...BC LONG TERM...NV AVIATION...JC/JE MARINE...BC/JMC/NV HYDROLOGY...BC/NV TIDES/COASTAL FLOODING...

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