Area Forecast Discussion
Issued by NWS Upton, NY

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308 FXUS61 KOKX 110936 AFDOKX Area Forecast Discussion National Weather Service New York NY 436 AM EST Sun Dec 11 2016 .SYNOPSIS... High pressure moves across into this morning, sliding offshore this afternoon. Low pressure well to the west moves into the Great Lakes with an associated warm front approaching the region. The warm front moves across the region late Sunday night. A cold front follows for Monday afternoon. High pressure then builds to the southwest of the region Monday night through midweek. For midweek, there will be a weak low moving to well north of the region and another weak low well offshore. An arctic cold front then follows Thursday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... High pressure traverses the region and moves offshore. Ridging aloft with jet stream lifting farther north. Ambient cold airmass will have little vertical mixing today with a lack of pressure gradient. Low to mid 30s for highs again. Dry initially, but chances for snow rapidly increase in afternoon with isentropic lift and moistening atmospheric column. Expecting a coating of snow in accumulation especially in areas at or below freezing. && .SHORT TERM /6 PM THIS EVENING THROUGH MONDAY NIGHT/... Moist boundary layer layer loses moisture in the mid levels later in the evening. Chances lower therefore from south to north for snow before more synoptic lift in the right rear quad of the upper level jet arrives overnight. This along with pva ahead of amplifying upper level trough will increase the lift. Widespread precipitation across the region overnight through Monday morning. Initially this will be snow, but with warmth arriving within first few thousand feet above surface, temperatures in the layer rise above freezing. For the most interior valleys, there will be a mix of snow and sleet as well as freezing rain while closer to the coast, snow will mix with rain. All rain with warm front lifting through Monday morning with last places to get above freezing being northern parts of the Lower Hudson Valley. The rain tapers off Monday afternoon into Monday night after the passage of a cold front. Westerly flow will advect in drier air allowing for a gradual decrease in clouds. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Upper air pattern will feature an anomalously high amplitude ridge over Alaska, which will allow the polar vortex to drop southward into central and eastern Canada by midweek. This will open the door for the coldest airmass of the season for the second half of the week. High pressure briefly follows for Tuesday with temperatures near seasonable levels. Another piece of Pacific shortwave energy races across the country. Global models vary with the amplitude of this feature with the nearly zonal flow in the southern branch of the polar jet. The amount of phasing with the northern branch looks to be the difference and 12z models have shifted towards a less phased pattern with the energy passing well south of the area. Have decreased pops to schc based on this trend. However...due to the fast flow, there is likely to be uncertainty in the magnitude of this system the next several days. Arctic air then spills southward on the backside of the system Thursday into Friday with daytime highs possibly not getting above freezing with overnight lows in the single digits to teens. These values are 15 to 20 degrees below normal. To make matters worse, strong NW winds will follow for Thursday producing very cold wind chill values. upper level trough moves onshore from the Pacific during the second half of the week. There are some differences aloft by Sat...although confluent flow across the country and developing low pres in the Plains could bring pcpn back to the region during Sat. The cold airmass already in place should all for pcpn to start in the frozen phase but will likely mix/changeover with sly flow. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... ***HIGH IMPACT WEATHER LIKELY LATE TONIGHT INTO MONDAY MORNING*** High pressure will move offshore today. A low pressure system will approach tonight. Light mainly WNW flow with broken high clouds early this morning to start. Winds will back SW-S this afternoon and increase close to 10kt as clouds lower/thicken, then light snow likely to develop this afternoon into early this evening, with medium probability for MVFR conditions, and low probability for IFR. A brief break in precip is possible late this evening. .OUTLOOK FOR 06Z MONDAY THROUGH THURSDAY... .Late Tonight...IFR conditions developing, with snow changing to rain at all terminals except KSWF. S winds G20KT late at KJFK/KISP/KGON. Here are the most likely snowfall accumulations: KSWF: Around 4 inches. KHPN/KBDR/KGON: Up to an inch. KISP/KJFK/KLGA/KEWR/KTEB: Only a coating of accumulation. .Monday...IFR conditions to start, becoming MVFR by midday NYC metros/KSWF, then VFR late. Snow changing to rain early at KSWF, and rain elsewhere, with precip tapering off in the afternoon. LLWS possible in the morning NYC metros/coast. S/SW winds G25-30KT in the morning at the NYC metros and KISP, becoming W in the afternoon. Chance for G40KT at KJFK/KISP in heavier rain in the morning. .Monday night-Tuesday...VFR. .Wednesday...Slight chance of MVFR conditions with any snow or rain showers. NW winds G25-30KT after midnight. .Thursday...VFR. NW winds G30KT. && .MARINE... As low pressure approaches tonight, S-SW winds will increase, and gusts to 35-40 kt are expected on the ocean waters and on the Long Island south shore bays, so gale warnings have been issued for late tonight into Monday for those waters. SCA also issued for the remaining waters through at least Monday mainly for post-frontal WSW to W flow gusting to 25-30 kt. Eastern Long Island Sound may see a few gusts up to 35 kt in the afternoon. SCA conditions will continue on the ocean and the eastern Sound/bays through Monday night, and ocean seas E of Fire Island Inlet may not subside below 5 ft til Tue afternoon or evening. After an Arctic cold frontal passage, SCA conditions should develop on the ocean Wed night, and on all waters on Thu. Gale force gusts may be possible on the ocean on Thu. && .HYDROLOGY... A half to three quarters of an inch of liquid equivalent precipitation is forecast late tonight through Monday. No significant pcpn (greater than 1/2 inch) is then expected through the end of the work week. && .TIDES/COASTAL FLOODING... With an approaching full moon...water levels will approach minor flood levels across the most vulnerable coastal locales of SW CT and the Western Great South Bay during the Monday morning high tide. Although southerly flow is not ideal...tidal departures of less than 1 ft are needed to reach minor thresholds in some spots. && .EQUIPMENT... New York City NOAA Weather Radio NWR transmitter KWO-35 is experiencing intermittent outages. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Winter Weather Advisory from 4 PM this afternoon to 10 AM EST Monday for NYZ067-068. NJ...Winter Weather Advisory from 4 PM this afternoon to 10 AM EST Monday for NJZ002. MARINE...Small Craft Advisory from 3 AM to 6 PM EST Monday for ANZ335- 338. Small Craft Advisory from 3 AM Monday to 6 AM EST Tuesday for ANZ330-340. Gale Warning from 3 AM to 6 PM EST Monday for ANZ353. Gale Warning from 3 AM to 1 PM EST Monday for ANZ355. Gale Warning from 6 AM to 1 PM EST Monday for ANZ345. Gale Warning from 6 AM to 6 PM EST Monday for ANZ350. && $$ SYNOPSIS...24/JM NEAR TERM...JM SHORT TERM...JM LONG TERM...24 AVIATION...Goodman MARINE...Goodman/24 HYDROLOGY...24/JM TIDES/COASTAL FLOODING... 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