Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 150510 AFDOKX Area Forecast Discussion National Weather Service New York NY 1210 AM EST Sat Dec 15 2018 .SYNOPSIS... A series of weak low pressure systems pass to the south of the area through the weekend while high pressure remains centered to the north. Low pressure will then be departing to the northeast Monday as a Canadian cold front passes through the area. High pressure then builds into the region through Wednesday, moving offshore Wednesday night into Thursday. Another frontal system impacts the region at the end of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Increasingly unsettled conditions are expected as a closed upper low slowly approaches from the southwest, and an upper trough passes to the north. Weak disturbances ahead of the systems and subtle isentropic lift in a warm advection regime will lead to the continued development of intermittent rain and/or drizzle through the night, with mostly cloudy conditions as a subsidence inversion remains. Have increased pops overnight a bit, mainly across the southern half of the forecast area based on latest trends in model guidance and radar imagery. The upper wave and attendant surface trough now moving through the eastern Canadian Provinces is expected to quickly be moving east of the area by morning, with confluent flow in its wake strengthening a surface high to our north in response. With the building high, any low pressure developing in association with the system to the southwest is likely to be shunted more to the south, with the northern edge of the pcpn shield also shifting south aft 12z. Temperatures will remain nearly steady overnight with lows in the upper 30s to mid 40s - around 5 to 10 degrees above climatological normals. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/... The approaching upper low to the southwest becomes the dominant system into the weekend, though attendant surface lows will still likely remain shunted farther south of the area as high pressure builds to our north. As a result, drier conditions than forecast may be possible as lower dew points advect southwestward. Upper divergence then sharply increases into the night as the system moves closer to the area, leading to better chances of precipitation by morning. Cloudy conditions should for the most part keep temperatures above freezing, though portions of northern Connecticut may come close Saturday night. If these areas can fall below freezing then freezing rain will be possible around sunrise. Expect highs in the upper 40s to lower 50s, and lows in the 30s to lower 40s. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... A progressive and amplified long wave pattern will remain across the country through the long term period. Split flow Sunday, with a northern stream longwave trough moving through eastern Canada and the northeast, and a southern stream closed low moving across the region, will become more phased Sunday night as the southern stream low moves off the New England coast. The northern stream ridge will be weakening as the southern low moves into the area, and the surface high. There still remains some uncertainty as to how quickly the high breaks down Sunday, and the timing of the low moving into the region. Late Saturday night into Sunday morning looks to be the best timing for the highest probabilities of precipitation as the mid level low moves over the area at this time. With strong lift with the low and the area in the left front region of a 40 to 60 kt 850 jet, there will be the potential for a period of moderate to briefly heavy rainfall. Also, there will be rather marginal elevated instability, so a rumble of thunder can not be ruled out. However, with the low chance and timing uncertainties will not mention in the forecast. Warm advection in advance of the southern stream low will allow thermal profiles to warm through much of the atmosphere and all liquid precipitation is expected with the series of lows into Sunday. Colder air will begin to be pulled into the region later Sunday night as the low departs, however, at this time the colder air will be confined to the northern zones with snow and a snow/rain mix as the low departs late Sunday night into Monday. With the passage of the northern stream shortwave Monday into Monday night and a Canadian cold front passing through, the area returns to below normal temperatures. Little moisture will accompany the passage of the front Monday and will keep area dry. However, there will be a chance of flurries across portions of the lower Hudson Valley. The longwave pattern remains progressive through next week. A lot of uncertainty develops in the guidance from Wednesday through Friday, with uncertainty in the timing of the high moving offshore and the strength and timing of the next northern stream frontal system. May be too quick to bring in chance of precipitation late Thursday, however, mainly followed WPC guidance due to uncertainties. && .AVIATION /05Z SATURDAY THROUGH WEDNESDAY/...
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Low pressure moving into the Mid Atlantic states tonight passes well south and east in the morning. High pressure briefly follows for Saturday afternoon/evening before another wave of low pressure approaches from the south late Saturday night. Widespread IFR conditions through mid morning as a storm system passes to the south and east with a period light rain, mainly near the coast in the morning. VFR conditions develop in the afternoon. Light and variable winds tonight become N/NE late morning into the afternoon, with a period of 15 to 20 kt gusts possible for NYC/NJ metro terminals. .OUTLOOK FOR 06Z SUNDAY THROUGH WEDNESDAY... .Saturday Night and Monday...MVFR/IFR in rain likely, possibly starting as FZRA at KSWF Sunday AM. Potential for wintry mix across interior terminals Sunday Night into Monday AM. Improving conditions Mon PM. Potential NE G20-25kt Sat Night/Sun becoming NW Sun Night/Mon. .Monday Night into Tuesday...VFR. NW Wind G20-30kt possible. .Tuesday Night into Wednesday...VFR. NW Wind G15-20kt possible.
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&& .MARINE... Seas remain between 3-4 ft this eve with sub-advsy conds expected into Sat. Easterly winds and gusts will then be increasing late Saturday night into Sunday as low pressure begins to deepen along the DELMARVA and mid Atlantic coast, with high pressure remaining to the north. There is the potential for a period of gale force gusts Sunday morning into Sunday evening on the ocean waters, with SCA gusts across the remainder of the forecast waters. A gale watch has been posted for the ocean waters Sunday and Sunday evening. Winds and gusts will diminish to below SCA levels across all the waters late Sunday night into Monday as low pressure departs. Then as colder air moves into the region Monday afternoon, behind a Canadian cold front, northwest winds and gusts increase to at least SCA levels across all the waters, with the potential once again of gale force gusts on the ocean waters Monday night into Tuesday. In addition, SCA level seas on the ocean waters will be on going Sunday morning with seas remaining elevated into Tuesday. && .HYDROLOGY... Between 0.50" and 1.25" of rainfall is expected through Sunday night. The highest rainfall amounts are currently expected across portions of northeastern New Jersey, NYC, and Long Island. A period of moderate to heavy rainfall will be possible Sunday morning. No widespread flooding is expected due to antecedent dry conditions in addition to the potential of a long break in any rainfall during the Saturday afternoon/evening time frame. && .EQUIPMENT... NYC Central Park winds are out of service until further notice. Loss of data is due to a severed cable. Parts are on order. NYC NOAA Weather Radio Station KWO35 (162.55 MHz) will remain off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Gale Watch from Sunday morning through Sunday evening for ANZ350-353-355. && $$ SYNOPSIS...MD/19 NEAR TERM...MD/24 SHORT TERM...MD LONG TERM...19 AVIATION...DW MARINE...MD/19 HYDROLOGY...MD/19 EQUIPMENT...//

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