Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 110548 AFDOKX Area Forecast Discussion National Weather Service New York NY 1248 AM EST Sun Dec 11 2016 .SYNOPSIS...
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High pressure settles over the region overnight into Sunday morning and then moves offshore Sunday afternoon. Low pressure then tracks across the Great Lakes Sunday night into Monday, sending a warm front through the region. A cold front then follows for Monday afternoon into Monday evening. High pressure briefly builds in for Tuesday before another low possibly impacts the area for the mid week period. An arctic cold front then follows behind the system Thursday.
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&& .NEAR TERM /THROUGH TODAY/...
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Slight adjustments were made to temperatures, dewpoints, and cloud coverage to better match observed trends. Overall, the forecast is on track. Mostly clear skies and light winds the first half of the overnight should allow temps to drop well down into the lower to middle teens across interior and Pine Barrens of LI. Generally lower 20s at the coast...except mid 20s NYC/Nj metro. Temps likely stabilize or even rise a bit towards daybreak as cloud cover increases. Mid level ridge axis slides across the region Sunday morning with a warm advection regime setting up as high pressure moves offshore. Models are continuing to indicate a swath of light snow potential along the initial surge of warm advection in the afternoon and early evening moving from south to north. There is also some support aloft from a strong upper jet to the north and some PVA as shortwave energy races eastward ahead of an upper trough across the Great Lakes. Increase in PoPs to high chance late in the day for much of the area with likely across the far NW interior. Thermodynamic profiles show moistening slowly through the afternoon. A dusting or a light coating of snow is possible within areas of light snow. Dry subcloud layer may hinder the development of snow as dew points may take some time to moderate. Followed a blend of guidance for highs as these seemed reasonable with increasing clouds and little vertical mixing. Highs in the lower to middle 30s are forecast.
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&& .SHORT TERM /TONIGHT THROUGH MONDAY NIGHT/... Initial surge of warm advection light snow moves off to the north between 00z and 06z. Models have been persistent in indicating mid level dry air behind this initial surge so the precipitation may end briefly before becoming widespread from west to east after midnight. Pattern recognition for the upcoming event Sunday night into Monday is one that does not favor a significant snowfall across the region. This is due to primary low moving through the Lakes into SE Canada and surface high moving offshore. Low level winds increase early Monday morning, surging temperatures upward. This warm push will help to bring a transition from snow to rain from south to north. Warmer air will begin to surge northward at the surface overnight with locations near the coast warming into the upper 30s and low 40s after midnight. This would be the majority of the precipitation will fall as rain with the main warm advection. Further inland across the NW interior, it will take a little longer for the warm air to arrive so a short period of accumulating snow is expected before transitioning to plain rain around or just after sunrise. Within the transition zone across the interior Lower Hudson Valley and NE NJ, a brief period of freezing rain is possible. Do not expect this to last long as temperatures will rise above freezing after sunrise with no damming high to the north to lock in the cold surface air. Models and ensembles have continued to come into better agreement overall over the last several cycles. Followed a blend of the 12z GFS/ECWMF for thicknesses and temperatures to formulate sensible weather grids. Through collaboration with neighboring offices, have issued a winter weather advisory for Orange and western Passaic counties Sunday evening into Monday morning. Confidence is highest in these zones for advisory level snow and with the addition of a brief period of freezing rain, the advisory was issued. Further east across in the interior, confidence is lower and through collaboration have decided to hold off on an advisory for now. Total snow less than an inch across NYC and the coast increasing to generally to 2 to 4 inches across the interior. Please see latest winter weather graphics at www.weather.gov/okx/winter. Plain rain is expected across the entire area from mid morning into the afternoon. Temperatures may touch 50 degrees near the coast and should be able to warm into the 40s even into Orange County. Rain ends from west to east late as the trailing cold front moves through. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Upper air pattern will feature an anomalously high amplitude ridge over Alaska, which will allow the polar vortex to drop southward into central and eastern Canada by midweek. This will open the door for the coldest airmass of the season for the second half of the week. High pressure briefly follows for Tuesday with temperatures near seasonable levels. Another piece of Pacific shortwave energy races across the country. Global models vary with the amplitude of this feature with the nearly zonal flow in the southern branch of the polar jet. The amount of phasing with the northern branch looks to be the difference and 12z models have shifted towards a less phased pattern with the energy passing well south of the area. Have decreased pops to schc based on this trend. However...due to the fast flow, there is likely to be uncertainty in the magnitude of this system the next several days. Arctic air then spills southward on the backside of the system Thursday into Friday with daytime highs possibly not getting above freezing with overnight lows in the single digits to teens. These values are 15 to 20 degrees below normal. To make matters worse, strong NW winds will follow for Thursday producing very cold wind chill values. Meanwhile...an upper level trough moves onshore from the Pacific during the second half of the week. There are some differences aloft by Sat...although confluent flow across the country and developing low pres in the Plains could bring pcpn back to the region during Sat. The cold airmass already in place should all for pcpn to start in the frozen phase but will likely mix/changeover with sly flow. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/...
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***HIGH IMPACT WEATHER LIKELY LATE TONIGHT INTO MONDAY MORNING*** Light WNW flow and mostly clear skies early this morning as high pressure builds in. High pressure moves offshore on today...with a low pressure system approaching tonight. Light WNW winds turn S in the afternoon. Light snow likely to develop Sunday afternoon into early evening with moderate probability for MVFR conditions likely...low probability for IFR. A brief break in precip possible late Sunday evening...before steadier and heavier precip moves in after midnight. .OUTLOOK FOR 06Z MONDAY THROUGH THURSDAY... .Late Tonight...IFR/LIFR conditions developing, with snow mixing with and changing to rain at most terminals. Brief FZRA possible at KSWF. LLWS possible late NYC metros/coast. S winds G25KT late at the NYC metros and KISP. Here are the most likely precip types and snowfall accumulations: KISP/KJFK/KLGA/KEWR/KTEB/KBDR/KGON: Snow changing to rain around midnight, with a coating to an inch accumulation. KHPN: Snow mixing with and changing rain to early Monday morning, with around an inch accumulation. KSWF: Snow with accumulation 3-4 inches with a brief period of freezing rain possible before going over to rain around daybreak. .Monday...IFR conditions. Wintry mix changing to rain in the morning at KSWF, and rain elsewhere. LLWS possible in the morning NYC metros/coast. S/SW winds G25KT in the morning at the NYC metros and KISP, becoming W in the afternoon. .Monday night-Tuesday...VFR. .Wednesday...Low chance of snow. NW winds G25-30 KT after midnight. .Thursday...VFR with NW winds G30kt.
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&& .MARINE... Winds and seas will continue to subside overnight...remaining below SCA levels into Sunday evening with high pressure in control. A warm front crosses the waters late Sunday night with increasing winds. Winds on the ocean should increase to SCA levels after midnight Sunday Night and then on all waters Monday morning with increasing southerly flow. Ocean seas will also increase above SCA. It is not out of the question for a brief period of gale conditions late Sunday Night into Monday morning. Winds and seas will gradually subside Monday night and conds should fall below advsy levels on all waters by Tue morning. Tranquil conds then prevail through Wed...then sca or even gale force gusts are possible behind an arctic front Wed night and Thu. && .HYDROLOGY... A half to three quarters of an inch of liquid equivalent precipitation is forecast late Sunday through Monday. No significant pcpn (greater than 1/2 inch) is then expected through the end of the work week. && .TIDES/COASTAL FLOODING...
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With an approaching full moon...water levels will approach minor flood levels across the most vulnerable coastal locales of SW CT and the Western Great South Bay during the Monday morning high tide. Although southerly flow is not ideal...tidal departures of less than 1 ft are needed to reach minor thresholds in some spots.
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&& .EQUIPMENT... New York City NOAA Weather Radio NWR transmitter KWO-35 is experiencing intermittent outages. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...Winter Weather Advisory from 4 PM this afternoon to 10 AM EST Monday for NYZ067. NJ...Winter Weather Advisory from 4 PM this afternoon to 10 AM EST Monday for NJZ002. MARINE...None.
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&& $$ SYNOPSIS...24/DS NEAR TERM...24/JM/DS SHORT TERM...DS LONG TERM...24 AVIATION...NV MARINE...24/DS HYDROLOGY...24/DS TIDES/COASTAL FLOODING... EQUIPMENT...

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