Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 180544 AFDOKX Area Forecast Discussion National Weather Service New York NY 1244 AM EST Mon Dec 18 2017 .SYNOPSIS...
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A warm front will approach overnight. Weak low pressure will then track along the front near or over Long Island on Monday. A cold front approaches on Tuesday, passes through the region Tuesday Night, with high pressure then building in for the mid to late week. A frontal system will likely affect the region for the weekend.
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&& .NEAR TERM /THROUGH TODAY/...
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Only change was delay for onset of precipitation by a couple of hours, especially farther to the north and east as high pressure remains across New England south to eastern Long Island. Light precipitation was developing ahead of the warm front through central New Jersey. 00Z KOKX sounding is fairly moist in the low-mid levels, except for a dry slot from around 700-600 hPa. Given this and still on track for a weak 700-500 hPa shortwave to cross the area overnight/early Monday morning ahead of a surface warm front, and remaining on track for being in left front quadrant of upper jet, appear to be set up for some spotty light precipitation overnight into Monday morning. Note: initial 00Z runs have trended slightly cooler in low levels thermally, so a little more snow and a little less sleet/freezing rain could occur than previously thought, however, with the bulk of the 00Z guidance still to come in, made no changes to headlines and only minor changes otherwise. A Winter Weather Advisory continues for areas where light freezing rain is expected, as even trace amounts can be hazardous and require an advisory. Along the south shore of Long Island and into the New York City area, a developing light onshore flow looks to allow for the transition to skip the freezing rain and go right to rain. These areas were therefore excluded from the advisory. There are a couple of ways the forecast can go wrong. The first is that precipitation just doesn`t materialize, as there is not a lot of strong lift with the system - this appears less likely. The second is that the precipitation ends before the warm nose allows for the transition to freezing rain - the chances of this seem to be increasing based on early 00z runs. The greatest threat for this occurring is along and west of the Hudson River where the precipitation should end quicker, and across eastern Connecticut, where the cold air may just remain entrenched. In any case, the threat of light freezing rain has been deemed high enough to warrant the advisory. Any precipitation ends Monday morning, with temperatures rising into the upper 30s and 40s as heights increase and southwest flow develops.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/... Westerly flow and lingering clouds will serve to limit low temperatures. With a lack of deep moisture and lift, the forecast has been kept dry. The Superblend was used for temperatures in order to account for the better low level mixing due to the wind. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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Models continue in good agreement with a broad but shallow northern stream trough approaching the NE on Tuesday and sliding through New England on Wednesday. At the surface, the primary low pressure/s will track through Quebec/Ontario with a trailing cold front approaching the region Tue, and crossing Tue Night. Models have continued dry with this frontal passage for the local region with the best forcing remaining north, and confluent upper flow over the region. The one thing to watch is late Monday Night into early Tuesday morning, the NAM is hinting at some stratus/drizzle with low- level saturation in the waa pattern. At this point, a low prob of occurrence, but if anything develops there would be a threat for light freezing rain across interior as cold air will have a tough time scouring out until daytime in this setup. 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 for Thursday, and then becomes ridged heading into Friday ahead of developing Western/Central Us troughing. At the surface, high pressure builds in from the west Wed into Thu, with dry and seasonably cold conditions. Models continue in agreement with a pattern shift to a more longitudinally oriented upper flow heading into the weekend, as several pieces of northern stream energy continue to dig a deep longwave trough into the Western/Central US. This may bring the coldest air of the season into the Central US and Rockies US by around Christmas. The noticeable trend versus 24 hours, is that the troughing has shifted a bit westward, with strong Western Atlantic/East Coast ridging. There is still agreement on energy across the 4 corners are mid-eek shearing towards the NE for the weekend, resulting in a a frontal system affecting the region for the weekend. If this trend holds, unseasonable warmth would be expected up the East Coast for this Christmas weekend. Quite a bit of model divergence thereafter on how this troughing and arctic air moves eastward for next week.
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&& .AVIATION /06Z MONDAY THROUGH FRIDAY/...
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A warm front approaches from the southeast early this morning, then lifts to the northeast by around midday. This front then stalls to the north into Monday night. Conditions lower to MVFR throughout early this morning. There is a low chance of IFR as well. Timing of changes in flight category could be off +/- 1-3 hours. Expect a spotty wintry mix to rain at KISP/KJFK/KLGA, spotty light snow at KSWF and a wintry mix elsewhere from overnight into Monday morning. There is some chance that precipitation could remain more in the form of snow/sleet vice freezing rain, especially at northern terminals. Precipitation should taper off from west to east 11z to 15z. Light and variable winds through this morning. Winds become W-SW this afternoon at under 10KT. Winds probably become light and variable again this evening at all but KJFK/KLGA/KEWR/KBDR/KISP with winds WSW-W at less than 10KT. .OUTLOOK FOR 06Z TUESDAY THROUGH FRIDAY... .late tonight...Mainly VFR with a very low chance for MVFR. .Tuesday-Tuesday night...Spotty MVFR possible into Tuesday evening, otherwise VFR. SW-W winds G20-35KT possible. .Wednesday-Thursday night...VFR. NW winds G20-30KT probable Wednesday/Wednesday night. .Friday...VFR with S winds G15-25kt possible, then MVFR or lower conditions and LLWS possible late.
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&& .MARINE...
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Forecast winds and seas remain as forecast. Updated to delay onset of light precipitation a couple of hours. With a warm front moving into the forecast waters predominate precipitation, especially across the ocean waters will be rain, with a wintry mix farther to the north. Winds and seas will remain below Small Craft Advisory levels through Monday as weak low pressure tracks in the vicinity of Long Island. Westerly flow may increase to 25 kt by late Monday night, especially on the ocean. Moderate potential for SCA conditions on Tue in strengthening SW flow and building ocean seas ahead of approaching cold front. Widespread SCA expected Tuesday Night through Wednesday with tight pressure gradient and caa in wake of cold front. Marginal gale gusts are possible Tuesday night into Wednesday. Conditions then should gradually fall back below SCA Wed night into into Thu, with relatively tranquil conds continuing into Fri as high pressure builds towards the waters. Next chance of SCA appears to be ahead of an approaching frontal system for the weekend.
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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...Winter Weather Advisory until 7 AM EST this morning for CTZ005- 006-009-010. Winter Weather Advisory until 9 AM EST this morning for CTZ007- 008-011-012. NY...Winter Weather Advisory until 7 AM EST this morning for NYZ067>071-078-079-177. NJ...Winter Weather Advisory until 7 AM EST this morning for NJZ002- 004-103>107. MARINE...None.
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&& $$ SYNOPSIS...JMC/NV NEAR TERM...JMC/Maloit/19/NV SHORT TERM...JMC LONG TERM...NV AVIATION...Maloit MARINE...JMC/Maloit/19/NV HYDROLOGY...JMC/NV EQUIPMENT...

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