Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 062115 AFDOKX Area Forecast Discussion National Weather Service New York NY 415 PM EST Tue Dec 6 2016 .SYNOPSIS...
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A low pressure center passes to our south tonight into Wednesday morning while a trough of low pressure moves through the tri-state area, this is followed by weak high pressure building in late Wednesday. Several re-enforcing cold fronts will cross the area from Thursday into Friday night, followed by high pressure building in Saturday and Saturday night. High pressure slowly retreats to the east early next week as a warm front approaches from the south Sunday and Sunday night, then lifts to the north Monday followed by a cold front pushing through Monday night. Another cold front approaches from the northwest on Tuesday.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Shortwave and trough aloft pass through tonight. At the surface, a low pressure center emerges off nearby the Del-Mar-Va Peninsula and shifts east out to sea. Meanwhile, a low pressure trough shifts through the tri state area overnight. The combination of lift and moisture will bring rainfall for the most part across the entire area. Thermal profiles could support PCPN other than rain for some of the interior. Some wet-bulbing is expected at the onset of PCPN, then the questions become how high the freezing level will be and how much warming happens the 950-900 mb layer thereafter. Feel that over the higher elevations of Orange County it will be mostly snow, but some sleet and rain is possible, more so late at night. A wintry mix is probable for the rest of the northernmost zones. Elsewhere, expecting rain. Without enough confidence to drop the winter weather advisory over Orange County, will leave it up, but it looks like a marginal event. Still think that elevations over 1000 ft could see up to 4 inches of snow. Lift weakens and mid levels begin to dry out late towards daybreak. The loss of ice nucleation aloft therefore makes it more difficult for snow formation during this period with light rain or possibly even drizzle becoming more likely wherever there is a wintry mix. Looks like just about all spots will be above freezing by the time this happens.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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Plenty of low level moisture lingers into early afternoon, but lift is weak...maybe just some large scale lift from an approaching jet streak. Low chances of light rain or drizzle, primarily during the morning. Clouds then diminish somewhat late in the day or early evening before increasing once again late at night. A blend of MOS guidance looked good for temperatures in the short term.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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A northern stream 850-500 hPa closed low tracks across Southeastern Canada Thursday through Friday bringing successive shots of re-enforcing cold air as shortwaves rotate around it through the region. The combination of strong low level cold advection and favorable low level flow from the Great Lakes will produce mainly isolated mainly rain showers (rain/snow showers far NW Orange County) Thursday, then a transition to mainly isolated snow showers from NW to SE Thursday night and continuing on Friday. Little or no accumulation is expected outside of higher elevations, where isolated 1-2 inch amounts are possible in any stronger convective bands which set up and linger over a given area. Note that higher elevations experiencing multiple prolonged convective snow bands could receive 1-2 inches per band experienced and not just 1-2 inches of snow total. At this time, it is too early to specify if and/or when and where any of these bands might occur, if they do at all. What is more certain Thursday-Friday is that much colder air will move into the region on gusty NW winds. Highs on Thursday will occur mainly in the morning, reaching the lower-mid 40s, with falling temperatures in the afternoon. Lows Thursday night should fall mainly into the 20s (lower-mid 30s Twin Forks of Long Island) with wind chills into the teens and lower 20s towards sunrise Friday morning. Highs on Friday will struggle to reach the mid 30s to around 40 over most of the region. A northern stream shortwave ridge should transit the area Friday night, bringing an end to any snow showers, followed by a brief period of zonal flow on Saturday - which also should be dry. A northern stream short wave passes Saturday night, but dry low levels should keep things dry. Northern stream ridging crosses the area Sunday, but could see strong enough low level warm advection by late Sunday to bring some light snow to far northern zones - for now lift does not appear strong enough over the remainder of the area for any precipitation Sunday afternoon. As is typical, there are differences between the models in how fast the warm front lifts to the north. The ECMWF and its idea of a slow warm frontal passage late Sunday night, is consistent with climatology which suggests that warm fronts very rarely lift north of Long Island at night, except maybe towards sunrise - so leaned towards the ECMWF Sunday night. As a result have a chance of snow across the interior and a chance of rain elsewhere for now Sunday night. This will be refined as exact extent of any cold air damming becomes better resolved with time (ECMWF currently hints at this at 12z Monday with kink in isobars to the S of Long Island - suggestive of at least a coastal front to the S if not a warm front). The region should become solidly in the warm sector Monday morning ahead of an approaching northern stream trough that passes to the east Monday night, bringing any showers to an end. Tuesday should be dry as northern stream ridging transits the area. Temperatures Friday night-Tuesday were based on the Superblend. They should run around 10 degrees below normal on Saturday, moderate to a few degrees above normal by Monday and then return to being below normal on Tuesday.
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&& .AVIATION /21Z TUESDAY THROUGH SUNDAY/...
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High pressure will move offshore giving way to low pressure approaching which will pass southeast of the area tonight. VFR will deteriorate to MVFR/IFR this evening with rain moving in. The rain becomes more of a drizzle overnight into early Wednesday and then some lingering low level clouds/patchy fog persist for Wednesday. There is some snow expected inland tonight with KSWF expecting to receive a period of light accumulating snow of a few inches. Winds are becoming more easterly near 10 kt with gusts expected to develop between 15-20 kt into tonight, mainly for coastal terminals. Winds become light Wednesday morning and into the early afternoon Wednesday with varying directions. Overall confidence with the forecast lowers tonight and even more for Wednesday because of the low confidence in wind direction forecast for Wednesday morning into afternoon. Timing of MVFR/IFR conditions could be 2-3 hours off from forecast. 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: Some occasional IFR conditions will be possible this evening. Gusts at times could be a few kts higher than forecast. KLGA TAF Comments: Some occasional IFR conditions will be possible this evening. Gusts at times could be a few kts higher than forecast. KEWR TAF Comments: Some occasional IFR conditions will be possible this evening. Gusts at times could be a few kts higher than forecast. KTEB TAF Comments: Some occasional IFR conditions will be possible this evening. Gusts at times could be a few kts higher than forecast. A chance of some brief sleet this evening with the onset of precipitation. KHPN TAF Comments: Some occasional IFR conditions will be possible this evening. Gusts at times could be a few kts higher than forecast. A chance of some brief sleet this evening with the onset of precipitation. KISP TAF Comments: Some occasional IFR conditions will be possible this evening. Gusts at times could be a few kts higher than forecast. .OUTLOOK FOR 18Z WEDNESDAY THROUGH SUNDAY... .Wednesday afternoon...MVFR improving to VFR with more westerly flow developing. IFR possible in the afternoon. .Wednesday night...Mainly VFR. .Thursday-Friday...Mainly VFR but isolated rain/snow showers could result in brief MVFR/IFR conditions. Gusty W-NW flow Thursday through Friday 10-20 kt sustained with gusts 25-30 kt, highest Thursday night and Friday. .Friday night...VFR. NW winds 15-20 kt, gusts up to 25 kt for the evening. .Saturday-Sunday...Mainly VFR.
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&& .MARINE...
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The pressure gradient increases as low pressure passes to the south of the waters tonight. Winds and seas therefore increase, with SCA conditions expected on the ocean waters. This should last into Wednesday morning, so will leave the SCA on the ocean unchanged. Looks like NY Harbor will fall short of criteria, so have dropped the SCA here. Relatively tranquil conditions then follow Wednesday afternoon and night. Small craft conditions are likely fro Thursday into Saturday due to strong low level cold advection with Gales possible Friday and Friday night. The risk of gales will be highlighted in the HWO. Conditions should fall below SCA levels on all waters by late Saturday and remain below into Sunday. Small craft advisory conditions are possible again by late Sunday on the coastal ocean waters.
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&& .HYDROLOGY...
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A half inch or less of liquid equivalent precipitation is expected tonight, then no significant widespread precipitation is expected Wednesday-Sunday. There is a chance of a widespread 1/2 inch or more of precipitation from Sunday night through Monday.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...Winter Weather Advisory until 6 AM EST Wednesday for NYZ067. NJ...None. MARINE...Small Craft Advisory until noon EST Wednesday for ANZ350-353- 355.
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&& $$ SYNOPSIS...JC NEAR TERM...JC SHORT TERM...JC LONG TERM...Maloit AVIATION...JM MARINE...JC/Maloit HYDROLOGY...JC/Maloit

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