Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 171348 AFDOKX Area Forecast Discussion National Weather Service New York NY 848 AM EST Wed Jan 17 2018 .SYNOPSIS... Low pressure tracks from south of Long Island into the Gulf of Maine today. High pressure then builds in from the southwest through Thursday, then to the south through Friday, and then moves into the western Atlantic this weekend. A warm front will slowly lift to the north on Monday, then a cold front will pass through on Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Models remain fairly consistent on large scale details, so general idea of a 700-500 hPa northern stream shortwave lifting NE through New England helps to lift a coastal low NE, as it slowly strengthens remains on track. With this general agreement on large scale, have focused on Hires models (WRF-ARW, WRF-NMM, HRRR, RAP, 3km NAM, HREF) for the details today. For now no changes are being made to winter related headlines, with only main change to snow totals being to increase over NE NJ, where there is some increase in confidence of a change over to all snow by 12Z, so this should allow for 1-3 hours of moderate snowfall there. Otherwise, main concern is where exactly does any banding set up. Most of the hires models suggest to the N/W of NYC, however there are a few that suggest could occur over northern portions of NYC including various runs of the HRRR and the 00z HREF. As a mitigating factor though, the NAM/GFS/ECMWF all have a 500 hPa vorticity minimum moving over NYC and vicinity around 12Z. If this is correct, this could serve to significantly limit snow totals during this time frame. Latest radar trends do show precipitation currently struggling to develop over eastern portions of NE NJ and NYC - so do see signs of vorticity minimum`s influence. The question remains can low level frontogenetic forcing over come the impact of the vorticity minimum. Noting some stronger returns all around the relative minima in reflectivity, there are some indications that this could happen. Given mixed signals in the data, will continue to monitor, but am prepared to make short fused adjustments to winter headlines and snow amounts if the evidence clearly points towards more snow over parts of NE NJ/NYC/coastal SW CT. So for now Winter Storm Warning remains for Orange/Putnam Counties with 4-7 inches expected, and a Winter Weather Advisory remains up for interior S CT and NE NJ and the remainder of interior Lower Hudson Valley for 2-4 inches of snow (locally up to 6 across interior S CT). High temps today should occur this morning, then low level cold advection in the wake of the coastal low should lower temperatures into this afternoon. As a result, cannot rule out all locations possibly ending as a brief period of snow. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... A closed 700-500 hPa low tracks across the Mid Atlantic States tonight, then to the SE of Long Island on Thursday, as northern stream shortwave ridging builds into the area. Given that the best forcing stays to the S tonight, and subsidence from the ridging on Thursday, it should be dry both periods. AS far as cloud cover goes, should see decreasing cloud cover tonight from W to E, then mostly sunny sky conditions on Thursday. Lows tonight should be up to 5 degrees below normal and highs on Thursday around 5 degrees below normal. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Surface high pressure will build to our south through Friday. An upper trough passing through Thu night into Fri morning should bring an increase in clouds but no precip. Temps on Friday should be slightly above avg. As low pressure passes to the north and high pressure to the south on Sat. expect a brisk W flow to develop, especially along the coast. These winds should weaken on Sunday as the low continues east. GFS and ECMWF disagree a little as to whether the flat upper ridge to the south or the flat trough to the north will prevail, but at any rate temps will continue to trend above avg into the weekend, with highs 45-50 if not a little higher. An amplifying but progressive upper trough entering the Plains states late this weekend will send sfc low pressure NE toward the upper Great Lakes. A leading warm front will approach our area late Sunday night into Mon, and its progress may be delayed by high pressure to the NE. There could be some spotty wintry precip inland late Sunday night into Mon morning, otherwise light rain into Mon evening. Followed slower model trend with a cold front trailing from the Great Lakes low, with its approach late Mon night into Tue. We could be setting up for a moderate to locally heavy rain event during this time as the low taps Atlantic moisture via a strengthening LLJ, with both it and difluent flow aloft likely providing enhanced lift, and a possible triple-point low passing nearby and concentrating low level convergence. && .AVIATION /14Z WEDNESDAY THROUGH SUNDAY/...
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A developing coastal low will move north and east of the region today, tracking just southeast of Long Island early on today, and then into the Canadian Maritimes this evening. IFR conditions across city and western terminals with low ceilings this morning as precipitation has developed across region. Visibilities also lower for the next few hours with this latest area of precipitation, especially where precip changes to snow. The precip will translate east throughout this morning. A burst of light to moderate snow for a 3 to 4 hour period from here on out this morning for the most part for city terminals. Any accumulation for the city terminals is with this band of moisture. All snow at KSWF with LIFR conds, which may be moderate at times through 14z. Between 5 and 7 inches of snow expected. For the remainder of the terminals, a quick slushy 1 inch or less of wet snow will be possible this morning, with LIFR-IFR conditions prevailing until the system moves east and precipitation ends. Conditions then improve from west to east through the afternoon, with VFR conditions and WNW winds becoming increasingly gusty through the evening. 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: Timing of snow tapering off and ending late this morning may be off by +/- 1 hour. Timing of VFR conditions may be off by +/- 1 to 2 hours this afternoon. The afternoon KJFK haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KLGA TAF Comments: Timing of snow tapering off and ending late this morning may be off by +/- 1 hour. Timing of VFR conditions may be off by +/- 1 to 2 hours this afternoon. The afternoon KLGA haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KEWR TAF Comments: Timing of snow tapering off and ending late this morning may be off by +/- 1 hour. Timing of VFR conditions may be off by +/- 1 to 2 hours this afternoon. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Timing of snow tapering off and ending late this morning may be off by +/- 1 hour. Timing of VFR conditions may be off by +/- 1 to 2 hours this afternoon. KHPN TAF Comments: Timing of snow tapering off and ending late this morning may be off by +/- 1 hour. Timing of VFR conditions may be off by +/- 1 to 2 hours this afternoon. KISP TAF Comments: Precipitation may end as a brief period of snow early this afternoon, but confidence is low. Timing of VFR conditions may be off by +/- 1 to 2 hours this afternoon. .OUTLOOK FOR 12Z THURSDAY THROUGH SUNDAY... .Thursday-Thursday Night...VFR. WNW winds G20KT on Thursday. .Friday...VFR. W-SW winds G15-20KT possible. .Saturday-Sunday...VFR.
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&& .MARINE... A moderate pressure gradient over the waters will allow winds on the ocean waters to reach up to 20 kt with gusts up to 25 kt through Thursday and over the non-ocean waters up to 15 kt with gusts up to 20 kt through Thursday. With seas on the ocean waters forecast to 3 to 7 ft as well, have extended the Small Craft Advisory (SCA) there through 6PM Thursday. Marginal SCA conds may continue on the outer ocean waters into Thu night and Fri. SCA conds are also likely Sat into Sat evening on the ocean as a moderate W flow develops between low pressure passing well to the north and high pressure building to the south. && .HYDROLOGY... No significant hydrologic impacts are expected through at least the upcoming weekend. A frontal system passing through Mon night into Tue has potential to bring over an inch of rain during that time. Mainly nuisance urban/poor drainage impacts expected attm. && .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...Winter Weather Advisory until 1 PM EST this afternoon for CTZ005>008. NY...Winter Weather Advisory until noon EST today for NYZ069-070. Winter Storm Warning until noon EST today for NYZ067-068. NJ...Winter Weather Advisory until noon EST today for NJZ002-004- 103>105-107. MARINE...Small Craft Advisory until 6 PM EST Thursday for ANZ350-353- 355. && $$ SYNOPSIS...Goodman/Maloit NEAR TERM...Goodman/Maloit SHORT TERM...Maloit LONG TERM...Goodman AVIATION...JE MARINE...Goodman/Maloit HYDROLOGY...Goodman/Maloit EQUIPMENT...

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