Area Forecast Discussion
Issued by NWS Upton, NY

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177 FXUS61 KOKX 130540 AFDOKX Area Forecast Discussion National Weather Service New York NY 1240 AM EST Wed Dec 13 2017 .SYNOPSIS... High pressure builds in overnight and Wednesday. A low approaches late Wednesday night and moves offshore Thursday. High pressure follows through early Friday. Low pressure develops southeast of the region late Friday and moves offshore Saturday. High pressure follows Sunday. Low pressure approaches Monday through Tuesday. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... With the initial arrival of the cold air, and onset of cold advection, wind gusts have peaked as high as 35 kt since 00Z. Gusts will then be 25 to around 30 kt through the overnight as cold advection weakens a little, and winds at the top of the mixed layer remain 25 to 30 kt. Overnight an upper trough, strong shortwave and surface trough shift in. Lift and CAA along with moisture from the ocean, LI sound, and even Lake Erie could produce snow showers over the area. Wind chills late tonight fall into the teens. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM THURSDAY/... Wednesday begins with an upper low over the Northeast and a deepening surface low entering SE Canada. There could be some snow showers over LI and SE CT in the morning before the upper low shifts east and overall lift diminishes. Dry, cold and windy otherwise. 850mb temperatures will fall to around -14 to -15C, but partial sunshine and a strong downsloping wind should somewhat temper the cold air mixing down from aloft. Highs expected to range from the upper 20s well inland to mid 30s for coastal sections. Wind chills start around 10 in the morning and average around 20 in the afternoon. It appears that wind gusts should fall short of advisory levels. Model consensus has the top of the mixed layer at 40-45 kt for a few hours during the midday hours so it would take just about complete efficiency for advisory-level gusts to mix down to the surface. Sustained winds could get close to advisory criteria for some coastal spots, but thinking is that this would not be a widespread event for any given forecast zone. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Amplified progressive pattern will under go some deamplification through the period. A series of shortwaves pass through roughly every 36 to 48 hours. The first feature will yield low pressure off the Mid Atlantic coast Thursday morning. Due to fast progressive flow and a lack of blocking, expecting this system to remain weak and not sufficiently develop until it is way offshore late Thursday. A light snowfall is therefore expected as any accumulations at this point looks to be light. The least chance of seeing minor accumulations at this time appears to be for far northern zones. Plenty of cold air in all levels, thus p-type is expected to be all snow. Recent model data has trended offshore for the most part with potential system for later Friday and Friday night. Thinking the new 12z Canadian which shows a decent low spin up closer to the coast is an outlier at this point, but later shifts will have to monitor model trends in case less energy gets sheared and the system stays in tack. A reinforcing shot of cold air will come in behind the departing low Friday night into early Saturday. Then the pattern undergoes deamplification with more of a semi- zonal look. Shortwaves will approach with similar timing as mentioned earlier, but should track further north as there associated frontal boundaries swing through. With some soft ridging temperatures overall should rebound to more seasonable levels for the second half of the weekend. A cold front will swing through sometime on Monday, but there are timing differences among models, which should be expected with very progressive nature of the flow. With warmer temperatures late in the period for Tuesday p-type may be wet along the coast, with a wintry mix inland with the system to remain relatively weak. No arctic air on the map late in the period as air of more pacific origin gets involved, paving the way for a stretch of more seasonable temperatures late in the period. && .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/...
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Deep low pressure tracks toward the Canadian Maritimes tonight as the cold front continues to move farther out into the Atlantic. A few widely scattered snow showers will be possible tonight but looking for mainly dry and VFR conditions. However, there may be some MVFR ceilings which will scatter out overnight. Brief W-NW gusts near 35 kt have been observed, but expecting most gusts to settle near 30 kt for overnight and pick up again for Wednesday, with gusts near 35 kt and perhaps a few gusts up to 40 kt. .OUTLOOK FOR 06Z THURSDAY THROUGH SUNDAY... .Wednesday night-Thursday morning...MVFR/IFR in snow, mainly overnight Wednesday night through early Thursday morning. W winds 15-20 kt gusts 25-30 kt Wednesday evening. W winds then decrease to 10-15 kt gusts to 20 kt overnight Wednesday night. .Thursday afternoon-Friday...Mainly VFR. NW wind G15-20kt into early Thursday night, then winds diminish. .Friday night...MVFR/IFR possible in snow. .Saturday-Saturday night...VFR. NW winds G20-25kt during day, G15-20KT during evening. .Sunday...MVFR or lower possible in rain/snow.
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&& .MARINE... With the onset of cold advection wind gusts on the ocean waters have reached 33 to 40 kt. Gale force wind gusts will continue through the remainder of the overnight as cold advection continues. Winds may diminish a few hours late tonight as winds at the top of the mixed layer subside. A gale warning will remain in effect overnight on the ocean waters, with a small craft advisory on the remainder of the forecast waters. Gale gusts become likely on all the forecast waters Wednesday. Looks like NY Harbor, Western LI Sound and the South Shore Bays will be falling below gales by Weds evening, so have shortened the warning to cover through the afternoon. SCA conds will otherwise prevail for those waters. The rest of the waters have been kept under a gale warning through Wednesday night, although some of these zones could get canceled at some point during the night. Therefore any advisories should be down for Thursday morning as pressure gradient relaxes. With low pressure developing and offshore seas building Thursday night seas may come up enough that a Small Craft Advisory may be needed, especially for southern and eastern marine zones. Another low pressure system intensifies Friday night into Saturday as it moves northeast off the coastal waters. Tightening pressure gradient and building seas will most likely yield Small Craft Advisories, with possible Gales for the ocean waters late Friday night and Saturday. Small Craft Advisories may very well stay up through Sunday into Sunday night with a sufficient gradient on a SW flow, especially for eastern most zones. && .HYDROLOGY... No significant hydrologic impacts expected. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 6 AM EST early this morning for ANZ330-335-338-340-345. Gale Warning from 6 AM this morning to 6 PM EST this evening for ANZ335-338-345. Gale Warning from 6 AM this morning to 6 AM EST Thursday for ANZ330-340. Gale Warning until 6 AM EST Thursday for ANZ350-353-355.
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&& $$ SYNOPSIS...GC/JC/JE NEAR TERM...JC/19 SHORT TERM...JC LONG TERM...GC/JE AVIATION...JM/JP MARINE...GC/JC/JE/19 HYDROLOGY...GC/JC/JE EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.