Area Forecast Discussion
Issued by NWS Upton, NY

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653 FXUS61 KOKX 171220 AFDOKX Area Forecast Discussion National Weather Service New York NY 720 AM EST Sun Dec 17 2017 .SYNOPSIS... High pressure moves over the region today, then drifts east tonight. A weak low tracks west and north of the area tonight and Monday with a warm front passing to the north. Another low passes to the north Tuesday into Wednesday. High pressure builds in late in the upcoming work week. A frontal system approaches by the start of next weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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The band of mid clouds across the lower Hudson Valley, into northern New Jersey, and most of Long Island were beginning to erode. However, unsure how much this will continue to occur. Also, higher clouds were beginning to move into the region well in advance of the next system to affect the region. So, will keep area mostly cloudy through the day. Only minor adjustments to the temperatures and dew points were made through today. Heights slowly rise through the day as the upper flow becomes more zonal. A shortwave moving out of the southern plains will weaken as this wave moves into the mid Atlantic. At the surface a weak open low will track to east of the Great Lakes with a weak warm front developing to the south of the area. Will keep precipitation out of the region through today.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... An open wave low will pass to the west and north as the northern stream remains nearly zonal and progressive. A weak warm front approaches tonight and moves north early Monday. There will be little forcing or moisture with the frontal boundary, and widespread precipitation is no longer expected. Precipitation more scattered and light. With warm air pushing into the cold air north of the warm front tonight, thermal profiles still indicating a possibility of a snow, rain, and freezing rain mix ahead of the warm front. Freezing rain will be brief and light, maybe more drizzle. With the uncertainty, brief timing, and low chance of occurrence, will not post any headlines at this time. Once the front moves north precipitation comes to an end. There is some uncertainty as to the timing of the warm frontal passage Monday morning, especially across the eastern zones. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... The northern stream remains nearly zonal into the beginning of the week as a couple of weak shortwaves moves through the flow. Then Tuesday a deeper northern stream trough digs into the Great Lakes and moves into the northeast. Much of the energy and lift with this system will remain to the north. And as a cold front drops south Tuesday and Tuesday night, there will be little moisture. So have removed the probabilities of precipitation Tuesday and Tuesday night. Upper trough swings through the NE Tue Night into Wed with a glancing shot of modifying arctic air in the wake of the cold front for Wed. Upper flow flattens and even becomes a bit ridged for Thursday ahead of the next northern stream trough digging into the Upper Plains. At the surface, high pressure builds in from the west Wed and across Thu, with dry and seasonably cold conditions. Models in general agreement with a pattern shift to a more longitudinally oriented upper flow heading into the weekend, as several pieces of northern stream energy begin to dig a deep longwave trough into the Western/Central US. This may bring the coldest air of the season into the Central US by around Christmas. Meanwhile, energy rounding this trough appears to send a frontal system through the region during the Fri Night- Sat Night time period. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/...
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High pressure over New England will move east through tonight as a warm front approaches from the SW. VFR through at least 03z tonight. SCT-BKN clouds ranging between 4-7kft expected into the aftn. Most guidance is indicating low clouds move into the area tonight (some hi-res guidance is only available through 04z attm), but have varying times. MVFR CIGS may develop several hours than forecasted in 12z TAFs. Light northerly winds become light and vrb this aftn and tonight (or a very light NE-E flow at NYC terminals aft 00z) as high pressure slowly builds eastward. There could be a few flurries or an isold light snow shower aft 03z tonight, which may temporarily drop conds to MVFR. Probability isn`t high enough to include in the forecast attm. .OUTLOOK FOR 12Z MONDAY THROUGH THURSDAY... .Mon...VFR returning in the morning. .Tue...MVFR CIGS possible during the aftn. SW winds 10-15G20-30KT possible. .Wed-Thu...VFR. NW winds G20-30KT probable Wed/Wed night.
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&& .MARINE...
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Seas at buoy 44097 (SE of Block Island) were 5.2 feet at 1100Z and seas at buoy 44017 were likely below small craft levels, so the advisory was allowed to expire. A period of tranquil conds will prevail on all waters through Mon night with a weak pressure gradient in place. The next chance for SCA conditions will be late Tue/Tue eve in SW flow ahead of approaching cold front, with high likelihood of widespread SCA Tuesday Night through Wednesday with tight pressure gradient and strong caa in wake of cold front. Marginal gale gusts are possible during this time frame. Conditions then should fall back below SCA heading into Thu as high pressure builds towards the waters.
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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...None.
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&& $$

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