Area Forecast Discussion
Issued by NWS Upton, NY

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876 FXUS61 KOKX 230544 AFDOKX Area Forecast Discussion National Weather Service New York NY 1244 AM EST Thu Feb 23 2017 .SYNOPSIS... High pressure over the western Atlantic will influence the weather across the Tri-State through Thursday. A mild, damp, spring-like pattern Friday and Saturday will give way to a more seasonal pattern for the beginning of next week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Main concern through this morning continues to be the development of dense fog. Cooling surface temperatures in combination with weak warm advection above the surface will create a strengthening temperature inversion. Low-level will continue to saturate beneath this inversion overnight into the early morning hours...especially across southern and eastern coastal areas...resulting in dense fog. Dense fog has already developed across eastern LI...with expectation for this to expand across coastal areas. This is supported by high-res models. Dense fog advisory has been issued through the morning hours. The fog and stratus should expand into the interior through the early morning hours...but lower confidence on it being widespread dense. Low temperatures will be in the upper 30s inland and low to mid 40s along the coast. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/... High pressure will remain across the western Atlantic, pumping a warm and moist southerly flow around it towards the local area. Aloft, a split flow pattern continues with core of northern stream well to our north and a slow moving upper low across the southeast states within the southern stream. Areas of fog and low stratus start the day on Thursday. The first forecast challenge is the duration. The fog should lift through the morning hours, but the stratus could hang on into the early afternoon. This creates another challenge with regards to temperatures. There is high confidence in seeing unseasonably warm temperatures for this time of year. However, how quickly clearing occurs will be important to how warm it gets away from the coast. Highs should be able to reach the middle and upper 60s north and west of the city where clearing occurs the quickest. In the NYC metro, readings will be in the lower to middle 60s. Further east across southern Connecticut and Long Island, temperatures will be held in the 50s to near 60 due to onshore flow. If the clouds clear quicker, then highs could end up warmer and some records could be broken. If clouds hang on longer, then highs could be held down several degrees from current forecast. For Thursday night, a weak boundary tries to move into the area from the north. The boundary likely stalls nearby overnight and acts as a focus for some areas of drizzle and fog development in a continued moist environment. There is also the chance of some rain along this boundary. Lows continue mild in the 40s to near 50 degrees. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Not much change to the forecast for Friday through Sunday. The operational models are catching up with the conceptual model of light rain and drizzle Friday night into Saturday. The timing of the cold frontal passage has been narrowed down to the first part of Saturday night, with the GFS now latching onto the ECMWF timing. The models are showing some weak elevated instability in the vicinity of the cold frontal passage. It would be preferred however to have some solid upper level divergence to get thunderstorms going. As a result, they have been left out of the forecast for now based on the progged position of the upper jet in the 12Z data. If the jet streak ends up further south, they may need to be reintroduced to the forecast. There remain some questions for Monday. The GFS continues to bring a system through with some snow and rain. The ECMWF is now clipping the southern portion of the forecast area. Considering the system is currently near Barrow, Alaska, model agreement is actually pretty good. Chances for precipitation have been set at 30 percent for this event. The pattern then shifts again with southwesterly flow aloft developing Tuesday and Wednesday. The timing of the warm front and associated low are progged in the Tuesday night and Wednesday period per the model consensus, so chances for rain have been included in the forecast. && .AVIATION /06Z THURSDAY THROUGH MONDAY/... High pressure remains off the Mid Atlantic coast overnight and through Thursday. The high drifts east Thursday night as a warm front develops north of the terminals. Terminals across eastern Long Island were LIFR in fog and stratus. The remainder of the terminals were VFR. However, the fog and stratus will develop and move north and west through the overnight with conditions lowering to MVFR and IFR, and LIFR. There is uncertainty as to how quickly and how low conditions will become farther to the west and north. After sunrise conditions will be slow to improve, eventually becoming VFR, which is expected sometime during Thursday afternoon. Again there remains a lot of uncertainty as to how quickly conditions improve. Possible that coastal terminals remain MVFR through the afternoon. Thursday night conditions lower again to MVFR and IFR in developing fog and stratus. Light and variable, to calm, winds at all terminals overnight, becomes S-SW less than 10 KT Thursday. .OUTLOOK FOR 06Z FRIDAY THROUGH MONDAY... .Late Thursday night-Saturday...MVFR to IFR in stratus and fog. Likely improving to VFR during the day Friday before lowering again Friday night. Chance of light rain or drizzle. .Saturday night...MVFR likely with rain. .Sunday...VFR. .Monday...VFR early...becoming MVFR. Chance of rain or snow. && .MARINE... Main hazard through Friday Night for ocean and at least southern and eastern nearshore waters will likely be dense fog as an unseasonable mild and moist airmass overspreads the cool waters. Otherwise, high pressure over the western Atlantic brings a weak pressure gradient and rather tranquil conditions to the local waters through Thursday night. Southerly wind gusts on the ocean could increase to close to 20 kt Thursday afternoon and evening. A southerly swell may also bring ocean seas to near 4 ft Thursday night. Otherwise, sub-sca conditions are expected. Winds and waves will remain below Small Craft Advisory levels Friday. Conditions will deteriorate Saturday, with criteria likely to be achieved Saturday night after a cold frontal passage. Small Craft Advisory conditions are then likely on Sunday, and possible on Monday. Winds and seas improve on Tuesday. && .HYDROLOGY... No hydrologic impacts are expected through Friday. Around an inch of rain is possible Saturday and Saturday night. Measurable precipitation is possible Monday and again Wednesday of next week. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Dense Fog Advisory until 10 AM EST this morning for CTZ011. Dense Fog Advisory until 10 AM EST this morning for CTZ010>012. NY...Dense Fog Advisory until 10 AM EST this morning for NYZ079>081- 179. Dense Fog Advisory until 10 AM EST this morning for NYZ078>081- 179. NJ...None. MARINE...Dense Fog Advisory until 1 PM EST this afternoon for ANZ330- 340-345-350-353-355. && $$ SYNOPSIS...12/DS NEAR TERM...JC/DS/NV SHORT TERM...DS LONG TERM...12 AVIATION...FEB/MET MARINE...12/JC/DS HYDROLOGY...12/DS is the U.S. government's official web portal to all federal, state and local government web resources and services.