Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 162328 AFDOKX Area Forecast Discussion National Weather Service New York NY 628 PM EST Fri Feb 16 2018 .SYNOPSIS... High pressure from the Central US builds into the region tonight into early Saturday, before sliding off the New England coast Saturday afternoon. A developing low pressure system Saturday will track to the Mid-Atlantic coast Saturday evening and then southeast of Long Island overnight Saturday into early Sunday. Low pressure then departs as high pressure passes to the southeast early next week. A warm front lifts northward, then a cold front passes late in the week. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Cold front south of Long Island with the precipitation quickly ending by 00Z. Updated to end precipitation earlier. Also, the colder air have been moving into the region with temperatures now falling several degrees per hour, with the drier air following. So updated both the temperatures and dew points for these latest trends. Slight ridging moves in tonight with the upper level jet streak moving a little farther north of the region. At the surface, high pressure from the central US will gradually build in from the west. Before the center of the high reaches the region, enough of a pressure gradient will exist to promote NW gusts to 25 to 30 mph advecting in colder and drier air.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Saturday will feature ridge axis moving offshore Saturday with a farther northward movement of the upper level jet streak. High pressure at the surface will center across the region Saturday morning before moving off the New England coast in the afternoon. The NW flow decreases with winds eventually swinging around to become E-SE. Daytime mixing will favors a little warm air advection in the afternoon with low level veering of winds. Now the focus will be Saturday night with track, magnitude and precipitation with a coastal low pressure area tracking southeast of Long Island. The upper level jet is shown by models to be quasi-zonal, SW to NE orientation, which will match the track of the low. This low pressure system initially was developing today in SW Pacific and this will have tracked through South Central US through Tennessee Saturday. From there, it heads ENE into the Mid-Atlantic Saturday evening and then deepens off the coast of the Delmarva by late Saturday night. It takes a track to the SE of the 40N/70W benchmark with boundary layer temperatures and the magnitude of deepening of the low crucial to the amounts of snow. The deeper the low, the more dynamic cooling there will be and this goes with the intensity of the snow as well. It`s a positive feedback loop, heavier snow would also force colder air to the surface. The timing of this event Saturday night leans more towards a colder solution compared if this were to occur during the day. Models have trended a little farther south with the low pressure center and without a large pressure gradient between the departing high and the approaching low, lowered snow amounts by around an inch. Also on this side of a slight decrease will be marginal boundary layer conditions at onset of snow. The temperatures will be slightly above freezing and unless the snow is quite intense, it will take an hour or so to decrease the surface temperature to wet bulb temperature. So for first 1-2 hours, snow may not accumulate much. Looking at a general 9pm to 3am timeframe for much of the snow to fall. Still see potential for banding with the snow with 1 inch per hour snowfall amounts possible, so 4-6 inch snow amounts forecast but with locally higher amounts possible. Where this streak of higher amounts occurs is quite uncertain at this time and that is why the winter storm watch was maintained and it can`t be ruled out over Orange and Putnam New York, so watch was expanded to those counties as well. Some higher snow accumulation in the 6 to 8 inch range was shown in the latest SREF but there are members on the lower end showing a few inches as well. Snow rapidly trends down from west to east early Sunday. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... Deep west/southwesterly flow aloft backs as western trough digs and eastern ridge builds early to mid week. The ridge flattens slightly late in the week as heights aloft fall. At the sfc, low pressure departs as high pressure quickly builds and passes offshore. A warm front passes to the north Monday, and the local area remains firmly in the warm sector Monday night through Wednesday. A cold front passes sometime Wednesday night or early Thursday, then high pressure builds to the north Friday. Global models appear to be in general agreement. As for sensible weather, dry conditions are anticipated Sunday, then rain accompanies the warm front Monday. While the area is in the warms sector, hit or miss light rain or drizzle is possible, as is nighttime and morning fog. Some rain may accompany the cold front Wed night, with another warm front approaching Friday. Temps rebound right away Sunday, then rise further Monday through Wednesday. There will be quite a temp difference west of the Hudson river (warmer), and along the south facing coasts (much cooler) as you would expect this time of year. Temperatures cool slightly behind the front Thursday into Friday. && .AVIATION /00Z FRIDAY THROUGH WEDNESDAY/...
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VFR through Saturday afternoon with high pressure building over the terminals. NW winds, primarily north of 310 magnetic, will continue to gusts 25-30 kt this evening. The gusts will gradually weaken after 03z and then end around 06-09z. The flow veers to the N-NE Saturday morning and then SE in the afternoon. Speeds will be under 10 kt. Conditions begin to deteriorate after 00z Sunday with an initial rain and snow mix becoming all snow. Forecast snowfall accumulations 00-06z Sunday are 2 to 4 inches. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Peak gusts 30-35 kt possible through 03z. Winds prevail north of 310 magnetic. KLGA TAF Comments: Peak gusts 30-35 kt possible through 03z. Winds prevail north of 310 magnetic. KEWR TAF Comments: Peak gusts 30-35 kt possible through 03z. Winds prevail north of 310 magnetic. KTEB TAF Comments: Peak gusts around 30 possible through 03z. KHPN TAF Comments: Peak gusts around 30 possible through 03z. KISP TAF Comments: Peak gusts around 30 possible through 03z. .OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY... .Saturday night...LIFR. Initial rain/snow mix near coast becomes all snow. All snow at KSWF/KHPN. .Sunday...VFR. .Monday...VFR becomes MVFR or IFR in rain and possible fog, especially late. .Tuesday...MVFR or IFR possible in the morning and again at night, otherwise VFR with SW wind G20KT possible. .Wednesday...Mainly VFR. Chance of showers/MVFR.
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&& .MARINE...
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Minor changes to the winds and gusts on the forecast waters for early this evening. Otherwise, no changes were made at this time. Surge of cold air behind cold front for this evening will allow for greater mixing across the waters. Most waters through the evening will gust 25-30 kt before decreasing overnight. Ocean seas will remain near 5 ft much of tonight. High pressure will move in for late tonight into Saturday and with the decreasing northerly flow, conditions will subside below SCA thresholds. The coastal low tracking southeast of Long Island will be weak in magnitude so winds are not expected to increase much Saturday night, keeping conditions below SCA. NW winds initially Sunday behind low pressure will back around to the south as high pressure builds and passes offshore. The south/southwesterly pressure gradient tightens Monday and Tuesday, and winds will begin to increase during this timeframe. Tranquil seas Sunday and Monday begin to build as the southerly winds pick up in speed. Expect 5 ft seas by Tuesday on the ocean waters.
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&& .HYDROLOGY... Around 0.3 to 0.6 of an inch of liquid equivalent is expected Saturday night with locally higher amounts. With most, if not all of this falling in the form of snow, no hydrologic impacts are expected. No significant hydrologic impacts are expected Sunday through the end of next week. && .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 Storm Watch from Saturday evening through Sunday morning for CTZ005>012. NY...Winter Storm Watch from Saturday evening through Sunday morning for NYZ067>075-078>081-176>179. NJ...Winter Storm Watch from Saturday evening through Sunday morning for NJZ002-004-006-103>108. MARINE...Small Craft Advisory until 1 AM EST Saturday for ANZ330-335- 338-340-345. Small Craft Advisory until 6 AM EST Saturday for ANZ350-353- 355. && $$ SYNOPSIS...JM/PW NEAR TERM...JM/19 SHORT TERM...JM LONG TERM...PW AVIATION...DS MARINE...JM/PW HYDROLOGY...JM/PW EQUIPMENT...

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