Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 140931 AFDOKX Area Forecast Discussion National Weather Service New York NY 431 AM EST Thu Dec 14 2017 .SYNOPSIS...
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A Clipper low will track to the south of Long Island this morning and then quickly continue out to sea. High pressure builds from the west tonight. A series of weak low pressure and frontal systems will pass through Friday through early next week, with high pressure building between each.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Vigorous vort max rounding the base of the mean trough early this morning. Overrunning pcpn is moving out of the area with a brief break and then pcpn associated with the upper shortwave moves back in for a few hours this morning. The surface low, over central PA as of 08z, will track south of the area this morning, which could help to enhance snowfall on Long Island. These features quickly translate east as the upper trough, vort max, and surface low move offshore 13-15z. Lift will also be maximized in the dendritic growth zone between 750 and 900 mb through around 14z across eastern Long Island. Guidance remains in good agreement with QPF, around 2 tenths of an inch on Long Island and around a tenth N and W. Snow ratios of around 15:1 near the coast and 17-18:1 across the interior still seem plausible given the temps. This would translate to 2-3 inches on Long Island and 1-2 inches N and W. There could be locally higher amounts with any enhancement or banding on Long Island, so it would not be surprising if a few spots reach closer to 4 inches. SREF plumes, NAM, NAM-3km, and HRRR continue to support this forecast thinking. Thus, the winter weather advisory remains in effect for Long Island through 10am. A special weather statement has been issued elsewhere, which highlights lower snow accumulation. Some impacts to the morning commute are anticipated, especially in the advisory area as temperatures early this morning are in the 20s. The snow ends on the east end around 15z with skies quickly clearing from west to east. It will become breezy as high pressure builds in from the west this afternoon. Highs well below normal ranging from the upper 20s to mid 30s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
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High pressure settles over the Tri-State Thursday night. With diminishing winds, mostly clear skies, cold airmass, and some snowpack on the ground, temperatures should bottom out in the lower teens and even single digits inland and middle and upper teens elsewhere (around 20 in the NYC metro area). The high moves offshore Fri aftn as the next shortwave trough and associated sfc low approach from the Great Lakes region with another low also developing along the Mid Atlantic coast. Have kept the PoPs from the previous forecast as it still appears pcpn could start to move into NW and SE areas late in the period. It is cold enough for snow. Highs on Fri will be similar to those today.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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The first in a series of upper level shortwaves in a progressive pattern pushes across the region Friday night into early Saturday morning. An offshore low develops well southeast of the area Friday night out ahead of the shortwave energy. While some light snow will be possible Saturday night, most if not all of the 00z forecast guidance keeps the bulk of the associated QPF offshore, and to our NW, closer to the inland parent low. Therefore, will continue to keep low chance POPs in the forecast. This shortwave passes Saturday as ridge builds, and remains in control through much of the weekend. The forecast becomes a bit more uncertain Sunday night through Tuesday as a series of weak shortwaves pass over the region. The latest 00z forecast guidance continues to show timing differences for each of these shortwaves along with their exact placement. Forecast guidance does however show each of these waves moving across the area with very low QPF values. So for now, will go with at least a chance or slight chance POPS Sunday night through Tuesday to account for the timing uncertainty. Surface high pressure and upper level ridging builds over the region for Wednesday and Thursday. Chilly temperatures continue Saturday and Sunday, then gradually warm closer to normal as zonal flow or weak ridging develops for Monday and Tuesday. Temperatures fall back below normal for Wednesday and Thursday.
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&& .AVIATION /09Z THURSDAY THROUGH MONDAY/...
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There will be a lull in the snow over the next few hours as the first batch of snow exits east. KGON will see snow through about 10Z before the first batch ends there. Though, there may be light snow to affect terminals from time to time during this lull, which is covered by a TEMPO group. Second round of snow comes generally around 12Z, with MVFR conditions returning. Some IFR conditions or lower are possible at times, with KISP having the best shot at seeing these conditions. VFR then returns for this afternoon into this evening. Snow accumulation 1-3 inches. Winds have diminished and gone light and variable or calm at many terminals. Winds will shift to the W-NW true Thursday behind the low with gusts redeveloping in the late morning and afternoon to 20-25 kt. Wind gusts diminish this evening. ...NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http://www.weather.gov/zny/n90 KJFK TAF Comments: MVFR conditions return 12Z or thereafter, with IFR conditions possible for brief periods during the heaviest of the snow through 14Z. Snow may end +/- 1 hour than is forecast. The afternoon KJFK haze potential forecast is GREEN, which implies slant range visibility 7SM or greater outside of cloud. KLGA TAF Comments: MVFR conditions return 12Z or thereafter, with IFR conditions possible for brief periods during the heaviest of the snow through 14Z. Snow may end +/- 1 hour than is forecast. The afternoon KLGA haze potential forecast is GREEN, which implies slant range visibility 7SM or greater outside of cloud. KEWR TAF Comments: MVFR conditions return 12Z or thereafter, with IFR conditions possible for brief periods during the heaviest of the snow through 14Z. Snow may end +/- 1 hour than is forecast. The afternoon KEWR haze potential forecast is GREEN, which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: MVFR conditions return 12Z or thereafter, with IFR conditions possible for brief periods during the heaviest of the snow through 14Z. Snow may end +/- 1 hour than is forecast. KHPN TAF Comments: MVFR conditions return 12Z or thereafter, with IFR conditions possible for brief periods during the heaviest of the snow through 14Z. Snow may end +/- 1 hour than is forecast. KISP TAF Comments: MVFR conditions return 12Z or thereafter, with IFR conditions possible for brief periods during the heaviest of the snow through 14Z. Snow may end +/- 1 hour than is forecast. .OUTLOOK FOR 06Z FRIDAY THROUGH MONDAY... .Thursday night-Friday...VFR. .Friday night...VFR. W winds G15-20KT develop towards early Saturday morning. .Saturday-Saturday night...VFR. WNW winds G20-25KT daytime and G15- 20KT evening. .Sunday...Mainly VFR. .Sunday night and Monday...MVFR or lower flight cat possible in snow/rain.
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&& .MARINE...
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Winds and seas have fallen below advsy levels on the eastern LI Sound and eastern bays, thus have cancelled the advsy. SCA conds will remain on the ocean waters for both winds and seas through the day, with winds diminishing this eve, and just residual seas remaining into tonight. Have extended the advsy through midnight tonight west of Fire Island Inlet and through 6am to the east, although they may fall below a few hours earlier. Could have gusts reaching 25 kt at times on eastern LI Sound and LI bays today, but not expecting them to be frequent enough to warrant the continuation of SCA. Sub-advsy conds all waters on Fri. Low pressure develops Friday night just east of the waters and deepens as it departs Saturday, with increasing westerly winds, and building seas expected behind it. Winds abate and seas subside as high pressure builds Saturday night through Sunday. Winds and seas remain below SCA levels Monday and Tuesday. Winds and seas build back to SCA levels Tuesday night and Wednesday as the pressure gradient increases behind a departing low and approaching high pressure system.
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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...Winter Weather Advisory until 10 AM EST this morning for NYZ078>081-177-179. NJ...None. MARINE...Small Craft Advisory until midnight EST tonight for ANZ355. Small Craft Advisory until 6 AM EST Friday for ANZ350-353.
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&& $$

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