Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 230810 AFDOKX Area Forecast Discussion National Weather Service New York NY 410 AM EDT Fri Sep 23 2016 .SYNOPSIS...
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Weak high pressure pushing farther offshore will be proceeded by the approach of a cold front towards the local region. This cold front will move across this evening from north to south. Strong high pressure from Southeast Canada gradually builds in behind the front through the weekend. High pressure builds slides offshore Monday. A slow moving frontal system could impact the area from Monday night through Thursday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Upper level features the southward shift of a longwave trough and jet stream across the Northeast. At the surface, a weak pressure gradient will be in place going into morning and then the flow becomes more SW-W ahead of the approaching cold front from the north. The SW-W flow, while light, will lead to a very warm day as clouds will be slow to increase and infiltrate from the north. With the same airmass across the region the last few days, overall average temperatures have sided with the warmer MOS guidance. With the expectation of nearly full sunshine through much of the day, the forecast used higher sides of guidance. In this case, this forecast used the MAV/ECS with some minor adjustments up around NYC. There is a moderate risk of rip current development at Atlantic Beaches today.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
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Aloft, the upper level trough and jet stream move farther south into the region with associated height falls. At the surface, the cold front moves across tonight from north to south during the evening hours. Showers are confined to along the boundary and behind the front, lingering out east perhaps through much of tonight while a more brief period is possible for western sections. In addition, multiple models show some negative Showalter indices moving across just behind the cold front. Therefore, this is suggesting some thunderstorms will be possible. With limited instability however, kept these isolated in coverage. Showers will be isolated to scattered, greater coverage farther east in the region. Without much of moisture sources to draw from, total rainfall is expected to remain quite light. Strong high pressure builds in behind the cold front. A northerly flow takes shape behind the front which will bring cold and dry air advection. This will allow for a cooler and drier airmass to build in for late tonight and Saturday. The lows tonight though will be limited though due to the lingering clouds which will mitigate radiational cooling. ECS guidance was used for lows tonight. For Saturday, the northerly flow continues with dry weather returning that morning through the rest of the day. There could be a few showers remaining out east during the early morning but otherwise expecting a dry day. It will also be remarkably cooler with highs only in the upper 60s to mid 70s, closer to normal than recent days. MET guidance was used for this to depict some southern coastal locations getting downslope flow and relatively higher temperatures.
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&& .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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The region will be under northwest flow aloft Saturday night-Sunday night as it remains in between a cutoff low slowly lifting through the Canadian Maritimes and a deep layered ridge moving into the Great Lakes and Ohio Valley. It should be dry with minimal cloud cover as a result. Lows Saturday night were based on a blend of MAV/MET/ECS guidance and NAM 2-meter temperatures, weighed towards the coolest guidance outside of urban areas to reflect likelihood of decent radiational cooling conditions (did adjust normal cold spots down a tad more than the blend above would suggest). Lows should be generally around 5-10 degrees below normal. Highs on Sunday were based on a blend of MAV/MET guidance, NAM 2- meter temperatures and a mix down from 875-825 hPa per BUFKIT soundings. Highs should be around 5 degrees below normal. Lows Sunday night were based on a blend of MEX/MEN/ECE/ECM/EKD/WPC guidance and NAM 2-meter temperatures weighed towards the coolest guidance outside of urban areas. Lows should be around 5-10 degrees below normal. The deep layered ridge axis builds over the area on Monday, keeping things dry. Cloud cover should be minimal until maybe late in the day, when some high clouds could begin to build into far western zones. The models continue to differ greatly in their handling of the Omega block over the country early next week and the developing cutoff low that should come down from central Canada towards the middle of next week. The CMC is the strongest with the ridging in the middle of the block and keep things dry until Tuesday night, the ECMWF is weakest with the ridge and brings in precipitation Monday night, with the GFS in between. Noting that multiple cutoff lows are involved with this pattern, there likely will be quite a bit of model spread for several more days. Even though the ECMWF has been fairly consistent over the past 3 runs in how it has handled the system, it is likely too progressive given the relatively high amplitude of the forecast Omega block and the fact that multiple cutoff lows are involved - both of these factors typically favor a less, not more progressive movement of systems. As a result only bring slight chance pops into the NW 1/3 of the CWA late Monday night. With decent overlap in precipitation coverage between the ECMWF and GFS on precipitation coverage 12-18z on Tuesday over roughly western 1/2 of the CWA - do have chance pops there. Otherwise have slight chance pops CWA wide from Tuesday- Thursday. Though there is at least moderate confidence that there will be some rain over the entire area in this time frame, confidence in exactly when any rainfall will occur is too low at this time to warrant higher pops. Temperatures Monday-Thursday were based on the Superblend and start out below normal Monday, then generally run within a few degrees of either side of normal from Monday night-Thursday.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/... VFR as high pressure slides south and a cold front approaches from the north this AFTN. The front passes through this evening with some SCT -SHRA (with a very low CHC for TS) mainly N and E of the NY Metro in its wake. Light winds this morning back to W (SW along the coast) by AFTN. Winds at KEWR may reach 10 KT between 20Z and 23Z and the direction could be WNW (~290 degrees), but gusts do not seem likely to occur. Timing of Cold FROPA with distinct wind shift to the NNE may be 1-2 hours sooner than fcst this evening. .Outlook for 06Z Saturday through Tuesday... .SAT-MON...VFR. .TUE...VFR. CHC -RASH late. && .MARINE...
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Light winds and ocean seas staying near 3 to 4 ft through today without much of a pressure gradient will increase tonight into Saturday behind the cold front. The vertical mixing will increase with the cold and dry air advection late tonight into Saturday. There will be higher chances of SCA conditions on the ocean due to both winds and seas late tonight and then Saturday mainly for seas. The non-ocean waters will experience the SCA wind gusts late tonight with seas remaining below SCA criteria. Wind gusts decrease for the non-ocean waters Saturday, with gusts early Saturday there still reaching 20 kt. There is some uncertainty with this abut felt SCA conditions would be frequent enough to warrant SCA issuance. A light to moderate pressure gradient over the waters Saturday night- Tuesday will keep sustained winds to 15 kt or less and gusts less than 25kt. It is possible, depending on exact strength of winds and the extent of swells on Saturday night-Sunday that the coastal ocean waters could see seas up to 5 ft. Otherwise, seas and waves are expected to be below Small Craft Advisory thresholds Saturday night through Tuesday as well.
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&& .HYDROLOGY...
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Rain showers associated with the cold front passage will be less than a quarter of an inch, mainly in the Friday night into early Saturday timeframe. Otherwise, mainly dry through Saturday. It should also be dry from Saturday night through at least Monday evening.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from midnight tonight to 6 AM EDT Saturday for ANZ330-335-338-340-345. Small Craft Advisory from midnight tonight to 6 PM EDT Saturday for ANZ350-353-355.
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&& $$ SYNOPSIS...JM NEAR TERM...JM SHORT TERM...JM LONG TERM...Maloit AVIATION...Tongue MARINE...Maloit/JM HYDROLOGY...Maloit/JM

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