Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 151109 AFDOKX Area Forecast Discussion National Weather Service New York NY 609 AM EST Fri Dec 15 2017 .SYNOPSIS... High pressure shifts offshore this morning as low pressure over the Carolinas tracks to the Mid Atlantic coast. This low will strengthen as it tracks northeast through the evening and continues out to sea tonight. High pressure then builds in through Sunday. A series of weak low pressure and frontal systems will pass through mid week. && .NEAR TERM /THROUGH TONIGHT/...
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Forecast is on track. Some suburban and rural locations have radiated quite well early this morning, Westhampton Airport dropped to 2 degrees at 10z!! Have made some minor adjustments to hourly T/Td the next few hours, which should rebound quickly after sunrise. Otherwise, high pressure over the area this morning, will shift offshore as the energy from both the northern as southern streams approach from the west consolidating near the Mid Atlantic coast this aftn and eve. Weak low pressure currently over interior portions of the Carolinas will gradually track towards the VA/ N. Carolina coast this morning and continue NE while strengthening this evening. Guidance is in good agreement that the low passes outside of the 40N 70W benchmark, but it`s pcpn shield will overspread the area in the form of snow mid- late afternoon, just in time for the evening commute. 00z guidance has come in wetter than previous runs, especially at the coast with QFP values ranging from a tenth to a quarter of an inch, highest values over eastern Long Island. There will be some fluff factor with temps ranging from mid 20s to lower 30s at the onset although the lower temps will be N and W of NYC, where lower amounts of pcpn are expected. Most of the Lower Hudson Valley, northern portions of NE NJ and interior SW CT are expected to see less than an inch with the rest of the area (except eastern Suffolk) ranging between 1 and 2 inches. A winter weather advsy has been issues for eastern Suffolk County with accumulations of 2-3 inches expected. Snow tapers off from W to E between 00z and 06z tonight with clearing and increasing winds as the pressure gradient tightens between the strengthening departing low, and strong high pressure over the SE US. Another chilly night with lows in the ranging from upper teens well inland to mid 20s at the coast.
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&& .SHORT TERM /SATURDAY/... Mean trough axis shifts offshore on Sat with gradual rising heights aloft. Could see some lake/ocean effect streamers come close to the forecast area, although high res guidance is not indicating we will be impacted by these. Right now, just expect an increase in cloud cover during the day. Otherwise, a breezy westerly flow and weak WAA should help temps rebound into the 30s. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Fairly good agreement with the operational models in the long term. Generally, zonal flow in the upper levels through the middle of next week, allowing for a progressive pattern. At the surface, high pressure moves overhead during the day Sunday and then pushes offshore Sunday night. This allow a warm front to approach and lift north of the area from Sunday night through Monday morning. Light overrunning precipitation will occur during this time frame. Models differ somewhat on timing. Uncertainty will also lie in precipitation type. Best chances for frozen would be inland areas, with a rain/snow mix along the coast changing to plain rain late Sunday night. The rain/snow line will move north Monday morning, with plain rain expected everywhere by Monday afternoon. Little, if any accumulation is expected with QPF amounts of only a few hundredths of an inch. Surface cold front then approaches Monday night and pushes through Tuesday. Warmer temperatures expected on Monday and Tuesday with warm air advection continuing out ahead of the front in the warm sector of the frontal system. Temperatures will be slightly above normal on Monday, and a few degrees warmer on Tuesday. Cooler temperatures for Wednesday and Thursday. Conditions will become breezy for Tuesday night into Wednesday as the pressure gradient tightens between the parent low from the cold front that tracks into the Canadian maritimes and the high pressure building in from the southwest. && .AVIATION /11Z FRIDAY THROUGH TUESDAY/...
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High pressure slides east this morning, giving way to an area of low pressure passing south of the region this evening. VFR this morning. Clouds gradually thicken and lower late this morning and afternoon. Snow then overspread the terminals after 18Z, with conditions falling to MVFR and eventually IFR for the late afternoon and evening. Expect a widespread 1-2 inches, except at KSWF where less than 1 inch is expected. Snow ends and conditions return to VFR between 03z-06z. light and variable winds this morning become westerly at 5-10 kt this afternoon. Winds increase tonight with some gusts to 20kt after midnight. 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: Best chance of snowfall expected between 21z-03z with 1-2 inches of accumulation. The afternoon KJFK haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KLGA TAF Comments: Best chance of snowfall expected between 21z-03z with 1-2 inches of accumulation. The afternoon KLGA haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KEWR TAF Comments: Best chance of snowfall expected between 21z-03z with around 1 inch of accumulation. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Best chance of snowfall expected between 21z-03z with around 1 inch of accumulation. KHPN TAF Comments: Best chance of snowfall expected between 21z-03z with around 1 inch of accumulation. KISP TAF Comments: Best chance of snowfall expected between 21z-03z with around 2 inches of accumulation. .OUTLOOK FOR 06Z SATURDAY THROUGH TUESDAY... .FRI NGT...VFR. A few W winds G20KT late. .SAT...VFR. WNW winds G20-30KT daytime. .SUN...VFR during the day. Chance MVFR in -RA/-SN towards midnight. .MON...Low chance MVFR in -RA for coastal terminals, light wintry mix inland. .TUE...MVFR possible. Slight chance of light -RA.
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&& .MARINE... Winds and seas have subsided on the ocean early this morning, thus the SCA has been cancelled. A brief period of tranquil conds on all waters today as high pressure over the NE moves offshore. The pressure gradient will tighten tonight as low pres passes S and E of the waters. SCA conds are expected to develop around midnight and continue through Sat, with the potential for gale force gusts on the ocean waters late tonight and into Sat. Have issued a gale watch for this potential, although it currently looks marginal. Could also have a few hours of 35 kt on eastern LI Sound during the day Sat, but didn`t have the confidence to include in the watch. Winds and waves diminish Saturday night as high pressure builds in. Waves come down below 5 ft across all ocean zones late Saturday night. Waves then build to above SCA criteria late Tuesday into Tuesday night as a cold front moves through and winds increase behind the cold front. Waves build to 5 to 9 ft on the ocean by Wednesday and diminish thereafter through Thursday. Windy conditions expected late Tuesday through Wednesday and at least part of Wednesday night as the pressure gradient increases. SCA winds likely across all waters through this time period. Gales are possible during this time frame as well, but there is still uncertainty this far out. && .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... CT...None. NY...Winter Weather Advisory from 1 PM this afternoon to 1 AM EST Saturday for NYZ079-081. NJ...None. MARINE...Small Craft Advisory from 11 PM this evening to 6 PM EST Saturday for ANZ330-335-338-340-345. Gale Watch from late tonight through Saturday afternoon for ANZ350-353. Gale Watch from late tonight through Saturday afternoon for ANZ355. && $$

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