Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 150536 AFDOKX Area Forecast Discussion National Weather Service New York NY 1236 AM EST Sun Dec 15 2019 .SYNOPSIS... High pressure builds in overnight, behind a storm departing to the north, and remains across the region through Sunday night. A low pressure system impacts the region Monday through Tuesday, then departs to the northeast Tuesday night. High pressure builds into the region on Wednesday and remains over the area through the end of the week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Dewpoints, temperatures, and sky cover were adjusted to better match current observed trends. Otherwise, forecast is on track. Low pressure will continue to move farther north of the forecast area overnight. Drier air behind an associated frontal boundary was advecting on a gusty west flow. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... High pressure slowly builds into the region Sunday. Continued breezy with high temperatures a couple of degrees above normal courtesy of a downsloping wind flow. As for PCPN, will go with a dry forecast, but might eventually need to add in sprinkles north and west of the city as shortwave lift interacts with some moisture arriving from the Great Lakes. The ridge of high pressure reaches us late at night Sunday with winds becoming lighter. Dry weather continues through the period. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... STORM SYSTEM MONDAY THROUGH TUESDAY NIGHT... A low pressure system will be the focus of this time period. Central low develops Mississippi River Valley towards Tennessee Monday and will be deepening with an associated warm front moving into the local region. Monday afternoon into Monday evening, the region receives warm air advection aloft, isentropic lift, and widespread stratiform precipitation. 850mb freezing line moves north of Long Island and perhaps some of the interior Monday evening and eventually north of the entire region by Tuesday morning. Onset of precip and first few hours, p-type likely will be snow, then a gradual changeover to a wintry mix and then to rain slowly from south to north. For Tuesday, the central low tracks directly across the local region. Precipitation continues through the day and tapers off behind the low late Tuesday afternoon into the start of Tuesday evening. For p-type, expecting all rain for coastal areas and a wintry mix for the interior. For a part of the day, the interior changes over to plain rain. Precipitation tapers off late. The low will be well east of the area, to North Atlantic waters offshore of Cape Cod by Tuesday night. Drying conditions are expected Tuesday night as the low deepens and accelerates northeast to eventually southeast of Nova Scotia by early Wednesday. For specifics, CONSRaw heavily utilized with temperatures, and dewpoints. More of an overall consensus weight used for Monday with temperatures and dewpoints. Temperatures will easily get to their wet bulb values once steady precip moves in Monday. Lowered ambient temperatures 1-2 degrees late Monday afternoon through Monday evening. Most snow accumulations will be Monday afternoon through Monday night, particularly between around 3pm and around 8pm for much of the coast when wet bulb temperatures will be below freezing. NYC and Long Island above freezing thereafter with slowly rising temperatures thereafter into early Tuesday. Forecast dewpoints are above freezing along the coast and NYC overnight through Tuesday. Mostly snow for interior from around 3pm Monday until around midnight. Thereafter it is wintry mix interior to rain at coast. Overall, forecast has a 1-4 inch snow event, with around a tenth of an inch of ice across interior. Upper level dynamics with this event convey an approaching longwave trough with a SW to NE jet streak Monday into Monday night. Upper level jet max moves across the local area Tuesday into Tuesday night. The upper level jet appears from the forecast models to be southerly dominant with not much phasing apparent in the mid levels. The associated parent low at the surface deepens about 10 mb from Monday afternoon into Tuesday evening. For the rest of the long term, high pressure starts to build back into the region on Wednesday and will remain over the area through the end of the week. Expect dry conditions with temperatures below normal. Low pressure may impact the area over the weekend. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... VFR as low pressure to the north continues pulling away today. Main concern will be gusty W winds, sustained 15-20kt with G25-30kt, with perhaps some ocnl G30-35kt. Winds should slowly diminish tonight. .OUTLOOK FOR 06Z MONDAY THROUGH THURSDAY... .Late tonight...VFR. .Monday...Snow with IFR conds becoming likely, mainly in the afternoon and especially for the NYC metros/KHPN/KISP. .Monday night...For the NYC metros and coastal terminals, mixed precip should gradually change to rain. For KHPN/KSWF, mixed wintry precip including sleet/freezing rain should change to rain late at KHPN. IFR possible. .Tuesday...Mixed wintry precip including sleet/freezing rain at KSWF should change rain. Rain elsewhere. IFR conds, possibly improving to MVFR in the afternoon. .Tuesday night...VFR. NW winds G20kt NYC metros/KISP mainly eve. .Wednesday...VFR. NW winds G25kt mainly afternoon. .Thursday...VFR. && .MARINE... No changes to winds and seas at this time. Winds pick up from the SW, then W tonight with a Gale Warning remaining on all waters. Gales should last through Sunday, and have extended the warning for the ocean, and eastern LI Sound/Bays into a portion of the evening. Winds then subside overnight Sunday with sub-advisory conds on all waters except on the ocean east of Fire Island Inlet. Conditions on the waters are below SCA Monday through very early Tuesday. Late Tuesday morning through Tuesday night, SCA conditions will become more probable across the ocean while non-ocean waters remain below SCA. SCA conditions are expected Wednesday and Thursday as winds and seas remain elevated. && .HYDROLOGY... Remaining flooding concerns are for the larger stem rivers in CT with a combination of the recent rainfall and melting snow to the north. Another significant rainfall event is possible Monday through Tuesday, with liquid equivalent QPF of 0.5 to 1.25 inches possible. There is uncertainty in this amount given uncertainty in the track of the low and frontal positions. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO35 (162.55 MHz) is still operating at reduced power. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Gale Warning until 6 PM EST this evening for ANZ335-338-345. Gale Warning until 10 PM EST this evening for ANZ330-340-350- 353-355. && $$ SYNOPSIS...JC/JM NEAR TERM...JC/JM/19 SHORT TERM...JC LONG TERM...BC/JM AVIATION...Goodman MARINE...JC/JM/19 HYDROLOGY...JC/JM EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.