Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 130015 AFDOKX Area Forecast Discussion National Weather Service New York NY 715 PM EST Tue Dec 12 2017 .SYNOPSIS...
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High pressure builds in tonight 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.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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At 23Z the cold front was just east of the CWA and with cold advection winds have begun to gust. The drier air behind the front was taking a bit longer to move in and have adjusted dew points upward through this evening. Late tonight 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.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/...
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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.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/...
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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.
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&& .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
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Deep low pressure tracks toward the Canadian Maritimes tonight as a cold front moves east of the region. Mostly rain showers will be scattered about initially but, by mid to late evening, there will be a mix of rain and snow showers. Mainly dry conditions are expected overnight into Wednesday. For KSWF, most showers if they occur would be snow showers. Mainly VFR for the TAF period but any of these showers will present a brief period of MVFR visibilities. W-NW flow continues tonight near 15-20 kt with gusts developing around 25 kt, increasing late this evening and overnight to 30-35 kt range, mainly for the city terminals. Outside of city terminals, wind gusts late this evening and overnight mainly in 25-30 kt range. Gusty west winds 20-25 kt will gust 30-35 kt for Wednesday. 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: MVFR possible this evening. Timing of gusts in 30-35 kt range could be off by 2-4 hours. KLGA TAF Comments: MVFR possible this evening. Timing of gusts in 30-35 kt range could be off by 2-4 hours. KEWR TAF Comments: MVFR possible this evening. Timing of gusts in 30-35 kt range could be off by 2-4 hours. KTEB TAF Comments: MVFR possible this evening. Timing of gusts in 30-35 kt range could be off by 2-4 hours. KHPN TAF Comments: MVFR possible this evening. Timing of gusts in 30-35 kt range could be off by 2-4 hours. KISP TAF Comments: MVFR possible this evening. Timing of gusts in 30-35 kt range could be off by 2-4 hours. .OUTLOOK FOR 00Z 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 G15-20 kt 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...
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No changes to the winds and seas at this time. It appears that gale force gusts, mainly on the ocean waters, could arrive a few hours before the time the previous gale warning was set to begin. Have therefore decided to start the gale warning on the ocean starting this evening. For the other waters it will be a close call. Perhaps occasional gusts to 35 kt late at night, but not enough confidence to bump up the timing of the start of the warning. SCA conds therefore prevail tonight with gales following through 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.
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&& .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 Wednesday for ANZ330-335- 338-340-345. Gale Warning from 6 AM to 6 PM EST Wednesday for ANZ335-338- 345. Gale Warning from 6 AM Wednesday 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 MARINE...GC/JC/JE/19 HYDROLOGY...GC/JC/JE EQUIPMENT...

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