Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 101637 AFDOKX Area Forecast Discussion National Weather Service New York NY 1137 AM EST Sat Dec 10 2016 .SYNOPSIS... High pressure continues to settle over the region this weekend. Low pressure then tracks across the Great Lakes Sunday night into Monday, sending a warm front through the region. A cold front will follow for Monday afternoon into Monday evening. High pressure will then briefly build in for Tuesday before another southern branch low possibly impacts the area for the mid week period. An arctic cold front then follows behind the system Thursday. && .NEAR TERM /THROUGH TONIGHT/... Forecast generally on track with minor changes to high temperatures as several locations near the city and on Long Island have already reached previously forecast highs. Readings will only rise a degree or so more from forecast as mid level clouds continue to increase this afternoon with approach of shortwave. Highs in the lower to middle 30s, around 10 degrees below normal for this time of year. Isolated flurries are still possible this afternoon with a bit better chance across Orange County. For tonight, the atmosphere will become drier with more subsidence as weak high pressure moves across the region. With this high being weak, going into daybreak Sunday, there will be mid to high level clouds moving in ahead of the next low pressure system. Used a less vast spatial variance with lows consisting of GFS MOS. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... High pressure slides offshore Sunday with an approaching warm front. The warm front moves across Sunday night into Monday with a subsequent cold front crossing Monday afternoon into early Monday evening. Main upper level shortwave with more amplified pattern and right rear quad of upper level jet moving in Sunday night into Monday. Dry conditions will be in place initially Sunday but the precipitation chances will rapidly increase from afternoon into evening. Initial precip type expected to be snow with cold airmass in place and wet bulb cooling. Then a transition to rain will take place from south to north Sunday night with some freezing rain across the interior. Monday the transition to rain continues for interior locations and the rest of the event is expected to be mainly rain. The rain tapers off Monday evening after the cold frontal passage. A more westerly flow will advect in drier air. Temperatures Sunday used the lower ECS and MAV guidance considering limited vertical mixing. Used raw model temperatures of ECMWF and NAM12 for Sunday night and Monday but for Monday blended it with GFS MOS. GFS MOS was used for Monday Night. Expect non-diurnal trend to temperatures Sunday night with temperatures slowly rising. Potential for interior locations to have 3-5 inches of snow and some locations near interior NE NJ and Lower Hudson Valley could see a period of freezing rain with light ice accumulations possible of under a tenth of an inch. Elsewhere, looking at near 1 inch of snow or less with mostly rain anticipated. Bulk of precip is Sunday night into Monday. && .LONG TERM /TUESDAY THROUGH FRIDAY/... 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 will briefly follow for Tuesday with temperatures just below 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. Due to the fast flow, there is likely to be uncertainty in the magnitude of this system the next several days. For now. will run with a chance of rain/snow Wednesday afternoon/night. 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. && .AVIATION /18Z SATURDAY THROUGH THURSDAY/... An upper level disturbance will move across today with BKN VFR cigs 040-060 this afternoon and early evening. Scattered snow showers/flurries possible with brief vsby reduction, most likely 18Z-21Z NYC metro and 20Z-23Z KISP. WNW flow left of 310 magnetic just over 10 kt with gusts 15-20 kt also expected. Expect diminishing winds and clearing skies thereafter. .OUTLOOK FOR 12Z SUNDAY THROUGH WEDNESDAY... ***HIGH IMPACT WEATHER LIKELY LATE SUNDAY NIGHT INTO MONDAY MORNING*** .Sunday...Mainly VFR. Chance of light snow in the afternoon with MVFR conditions likely, IFR possible late. .Sunday night...IFR/LIFR conditions developing, with snow mixing with and changing to rain at most terminals. LLWS possible late NYC metros/coast. S winds G25KT late at the NYC metros and KISP. Here are the most likely precip types and snowfall accumulations: KISP/KJFK/KLGA/KBDR/KGON: Snow changing to rain by midnight, with a coating to an inch accumulation. KEWR/KTEB/KHPN: Snow mixing with and changing to rain late, with 1-2 inches accumulation. KSWF: Snow with accumulation 4-5 inches. .Monday...IFR conditions. Snow mixing with/changing to rain in the morning at KSWF, and rain elsewhere. LLWS possible in the morning NYC metros/coast. SW winds G25KT at the NYC metros and KISP, becoming W in the afternoon. .Monday night...Still a chance of rain with MVFR or lower conditions early at KISP/KGON. otherwise VFR. .Tuesday...VFR. .Wednesday...Chance of rain, changing to snow at night. NW winds G20KT after midnight. && .MARINE... NW winds continue to gust on the ocean waters to 25 kt. Have extended the SCA for Sandy Hook to Fire Island Inlet until 4 pm. Winds should slowly fall below 25 kt this afternoon, but may last a bit longer east of Moriches Inlet. As a low pressure system approaches Sunday night, SW winds should increase, with SCA conditions becoming likely, and gales possible late at night into Mon morning. As the system passes, moderate W-NW flow should bring at least SCA conditions to all waters on Mon. Ocean seas will take longer to subside, and so SCA conds there should last into Mon night and possibly tue morning out east. Low pressure may develop over the Atlantic during mid week, which could bring at least SCA conditions Wed night behind an arctic cold front. && .HYDROLOGY... A half to an inch of liquid equivalent precipitation is possible late Sunday through Monday. && .EQUIPMENT... New York City NOAA Weather Radio NWR transmitter KWO-35 is experiencing intermittent outages. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 4 PM EST this afternoon for ANZ353- 355. Small Craft Advisory until 6 PM EST this evening for ANZ350. && $$ SYNOPSIS...JM NEAR TERM...JM/DS SHORT TERM...JM LONG TERM...DW AVIATION...Goodman MARINE...Goodman/DS HYDROLOGY...JM/DW EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.