Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 200916 AFDOKX Area Forecast Discussion National Weather Service New York NY 416 AM EST Fri Jan 20 2017 .SYNOPSIS...
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An upper level disturbance approaches today and weakens as it moves across tonight. 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.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Subsidence inversion around 925 mb continues to lock about a 1kft layer of moisture in the form of stratus. Main challenge this morning is if some of these clouds erode or continue to hang on. Trends have pointing to the clouds hanging on into the morning as depicted by thermodynamic profiles on the last several runs of the RAP and HRRR. Latest forecast calls for mostly cloudy to overcast skies this morning. The inversion begins to erode a bit late this morning and early afternoon so this should help diminish some of the low clouds. However, middle and high level clouds will be increasing ahead of the approaching southern stream shortwave energy. This will lead to a mostly cloudy sky condition this afternoon. A few breaks in the clouds should help temperatures rise into the middle and upper 40s this afternoon. Best lift associated with the southern stream shortwave energy arrives between 3 and 6pm across NYC metro, NE NJ, and Lower Hudson Valley. Have increased pops to categorical here with a fairly sharp gradient of lower further east as best lift and moisture lie in a narrow corridor. High probability of measurable precipitation on the latest ensembles and deterministic models supports categorical pops. Temperatures warm enough for plain rain, which will be on the light side.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
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Band of light rain progresses east this evening. Lift weakens as the shortwave weakens and gets trapped under buildings heights aloft. Pops diminish from west to east through night. A few hundredths to a tenth of inch total forecast with this system. Low level moisture lingers through the night and with weak flow some patchy fog is possible. Temperatures will not be able to fall too much due to linger clouds with lows forecast above freezing across the CWA. High pressure returns on Saturday. Mostly cloudy conditions continue in the morning, but should see enough breaks in the afternoon for some sun. With ridging building overhead, the airmass is quite warm. Highs should reach the lower and middle 50s. The only negating factor to seeing these temps would be if clouds hang on longer through the day, which some of the higher res model profiles indicate as a possibility.
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&& .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 /08Z FRIDAY THROUGH TUESDAY/...
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A disturbance moves across tonight with high pressure returning for Saturday. MVFR will be persistent throughout much of the period and with rain arriving this afternoon through the evening, there will be an increasing potential for IFR/LIFR tonight with residual low level moisture. Winds are relatively light through the period at less than 10 kt, gradually becoming more E-SE this afternoon into this evening and eventually more southerly later tonight. 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: Unsure of 15-20Z VFR period in TAF. This could have intermittent MVFR. KLGA TAF Comments: Unsure of 15-20Z VFR period in TAF. This could have intermittent MVFR. KEWR TAF Comments: Unsure of 15-19Z VFR period in TAF. This could have intermittent MVFR. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Unsure of 15-19Z VFR period in TAF. This could have intermittent MVFR. KHPN TAF Comments: Unsure of 15-20Z VFR period in TAF. This could have intermittent MVFR. KISP TAF Comments: Unsure of 15-19Z VFR period in TAF. This could have intermittent MVFR. .OUTLOOK FOR 09Z SATURDAY THROUGH TUESDAY... .Saturday-Saturday night...MVFR or lower possible early Saturday morning, followed by VFR for the late morning through Saturday night. .Sunday-Sunday night...MVFR or lower in -RA. IFR in any -SN inland. Moderate rain develops at night, mixing with snow for interior. NE gusts 20-25 kt by late Sunday afternoon and evening. NE gusts 30-40 kt Sunday night. .Monday-Monday Night...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. Gusts up to 20-25 kt.
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&& .MARINE...
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Easterly swell continues on the ocean waters with significant wave heights between 4 and 6 ft. They should subside over the next few hours, but will monitor trends to see if some of the SCA needs to be extended past 11z. Otherwise, a relaxed pressure gradient over the waters will keep winds and seas below SCA levels through Saturday 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... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory for hazardous seas until 6 AM EST early this morning for ANZ350-353-355. && $$ SYNOPSIS...Goodman/DS NEAR TERM...DS SHORT TERM...DS LONG TERM...Goodman/NV AVIATION...JM MARINE...Goodman/DS/NV HYDROLOGY...Goodman/DS/NV TIDES/COASTAL FLOODING...

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