Area Forecast Discussion
Issued by NWS Upton, NY

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KOKX 171542 AFDOKX Area Forecast Discussion National Weather Service New York NY 1042 AM EST Thu Jan 17 2019 .SYNOPSIS... High pressure settles in just north of the region today. Low pressure and a weakening warm front passes through tonight into Friday morning, followed by high pressure briefly building in late Friday and Friday night. A significant winter storm impacts the region late Saturday into Sunday and will be followed by arctic high pressure Monday into Tuesday. The next frontal system approaches the middle of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Forecast on track with just a few minor adjustments to reflect latest observations. A strong polar high pressure system just north of the area will be in control today providing dry and seasonably cold conditions. Temperatures closer to the coast are expected to get to, or near freezing. Temperatures inland and to the north will only get into the upper 20s to around 30. Used a consensus blend for today as there was general agreement amongst the guidance with the best cold advection taking place during this morning. Most of the numerical guidance is suggesting that clouds begin to overspread the region from the WSW to the ENE during the early afternoon, with lowering clouds into the evening. South and southwestern areas will be in and out of high clouds this morning, otherwise lots of sunshine to start, and then the clouds for the afternoon from a fast moving system approaching from the Tennessee Valley. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... A weak and broad area of low pressure will approach tonight along with some troughing aloft and shortwave energy. The energy in the southern branch of the jet stream is quite strung out and not all that impressive. The model consensus is for precipitation to start during the late evening, give or take a couple of hours from west to east. Not an impressive system with some of the BUFKIT profiles showing some gaps in the moisture, with the mid level forcing weak to say the least. Due to weak omega, in general snowfall amounts will not exceed two inches, and that may even be pushing it. Snowfall amounts on average should be around an inch, with very little for far southeastern sections, and up to about 2 inches in the hills in interior northwestern sections. POPs and QPF have backed down a bit with latest package, with QPF amounts generally around a tenth of an inch. With ground temperatures quite cold anything that falls should stick to most surfaces, even at the coast, at least to start. The low level profiles begin to warm getting closer to 11-12z Friday across southeastern coastal sections where a change to plain rain is likely towards daybreak, with a changeover to plain rain across the city likely during the mid to late morning just before the precipitation ends. Due to the timing of the snow, it will be a bit slick in spots, especially on secondary roadways to begin the Friday morning commute. If the snow does have any difficulty sticking it will be due to a lack of intensity, and not temperatures during the overnight. The back edge of the precipitation should clear the city by the late morning on Friday, and the early afternoon the latest across far eastern sections, with clearing setting up for late Friday afternoon into Friday evening as high pressure briefly sets up shop. West winds will blow slightly stronger behind the system, and can`t rule out a few gusts far east late in the day as the system attempts to intensify to some degree well offshore. Temperatures for Friday afternoon will actually nudge back to slightly above normal levels before the colder air returns into Friday night. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... The main concern in the long term is the significant winter storm for late Saturday into Sunday. This storm will be followed by the coldest air of the season. There is high confidence in a high liquid equivalent event, but confidence in PTYPE is much lower. Arctic high pressure will be located across southeast Canada and ridge down into New England on Saturday. At the same time, a southern stream shortwave spawns low pressure across the southeast. The southern stream is progged to remain progressive and positively tilted with little phasing from the polar jet to the north. It appears that the influence of the northern stream will not come into play until the southern stream wave is near the east coast. This has led to a consensus of a colder solution and a track of the low further south and east than the previous forecast package. Dprog/dt on the recent deterministic runs shows this general trend well except the GFS/GEFS which appear to be an outlier solution and remain much warmer than the rest of the guidance. The main energy with the southern stream wave will be coming onshore today. There is also sensitivity as noted above with the how much the polar jet interacts and phases with the southern stream, so changes in track forecast are still possible in subsequent forecast packages. Saturday will be dry through the afternoon then warm advection quickly takes shape with snow overspreading the region in the evening. The air mass in place at the onset will be supportive of all snow. Strong warm advection and an increasing southeasterly low level jet should bring in warmer air aloft to bring a transition zone. How quickly this occurs will be important along the coast for the amount of snow accumulation. This warm nose aloft will gradually spread inland to encompass the entire area Sunday morning. Even the colder model solutions still show this warming aloft due to the broad middle level low center tracking initially to our west Saturday night and then over the region Sunday morning. Precipitation should transition to plain rain for much of NYC, Long Island, and southeast Connecticut late Saturday night into Sunday morning. PTYPE for the rest of the area may transition to sleet and/or freezing rain depending on the depth of the low level cold below the warm nose. The colder solutions of the ECMWF and NAM out through 12z Sunday show potential for a quite deep cold layer below the warm nose, which would mean more sleet rather than freezing rain. It is too early to say for sure how this aspect will evolve, so for now will show a mixture of sleet and freezing rain for the interior Sunday morning. Once the low tracks east of the area, colder air rapidly rushes back in from the north and west and will bring a gradual transition back to snow as the precip ends. A significant snow and sleet accumulation of 6 plus inches appears likely across portions of the NW interior. The 00z ECMWF EPS probability of 6 inches or more is around 80 percent across this region. Amounts will decrease as one nears the coast with a few inches possible, but this will ultimately be dependent on how quickly the precipitation changes to a mix or rain. Significant freezing rain accretion is also possible Sunday morning, especially north and west of NYC. Please note that small changes in track will have significant implications for the type of precipitation and amounts. While forecast amounts of snow, sleet, and freezing rain are of lower confidence, there is higher confidence in a liquid equivalent of 2 to 3 inches. Temperatures rise into the upper 30s and low 40s along Long Island and southeast Connecticut Sunday morning, but will rapidly drop back below freezing in the afternoon and evening, any standing water could quickly freeze, creating hazardous travel conditions even where little wintry precipitation occurs. Temperatures will continue to plummet through the overnight hours, with lows Monday morning ranging from the single digits to near 10 degrees. Gusty northwest winds will result in wind chills around 5 to 15 degrees below zero. The lowest wind chills are most likely to occur across the interior. The arctic air remains in place on Monday as high pressure builds into the region. Highs will only be in the teens with wind chills staying 0 to 10 below. Temperatures should warm into to the 20s and low 30s on Tuesday and then potentially above normal on Wednesday ahead of the next system approaching the area. && .AVIATION /16Z THURSDAY THROUGH MONDAY/... High pressure gradually retreats into the Canadian Maritimes through tonight, as a weak coastal low approaches from the Mid Atlantic. High confidence in VFR through the evening push, then light snow and MVFR conditions developing W-E late this evening and into the overnight. IFR expected for at least a couple of hours late tonight. Warmer air in the low levels will result in a transition to a mix of snow and rain at coastal terminals near the end of the TAF period, although there could be a few hours of FZRA/FZDZ at NYC/LI terminals depending on how quickly surface temperatures rise. Timing of this could be a few hours off from current forecast. Light winds (less than 10 kt) through the TAF period. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http:/ KJFK TAF Comments: Timing in changes in wind direction could be off +/- 1-2 hours. The afternoon KJFK haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KLGA TAF Comments: Timing in changes in wind direction could be off +/- 1-2 hours. The afternoon KLGA haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KEWR TAF Comments: Timing in changes in wind direction could be off +/- 1-2 hours. The afternoon KEWR haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KTEB TAF Comments: Timing in changes in wind direction could be off +/- 1-2 hours. KHPN TAF Comments: Timing in changes in wind direction could be off +/- 1-2 hours. KISP TAF Comments: Timing in changes in wind direction could be off +/- 1-2 hours. .OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY... *** HIGH IMPACT WEATHER LIKELY SATURDAY NIGHT INTO SUNDAY NIGHT*** .Friday morning...IFR becoming VFR late morning. Light snow changing to rain at coastal terminals (FZRA/FZDZ possible early) before ending. KSWF/KHPN should remain all snow. Runway accumulations of about 2 inches at KSWF, and around an inch elsewhere. .Friday afternoon-Saturday morning...VFR. NW-N winds G15-20KT possible at night. .Saturday afternoon/evening...Becoming IFR or lower with snow developing from W to E. LLWS possible late. .Late Saturday night...IFR or lower conditions likely. Snow changing to rain at City/Long Island terminals and to a wintry mix at northern terminals. LLWS likely. .Sunday-Sunday night...IFR. Precipitation changing to all rain Sunday morning except possible continued wintry mix for Lower Hudson Valley Terminals. Precipitation changing back to all snow Sunday afternoon/evening before ending later Sunday night. LLWS possible in the morning. Flash freeze possible Sunday afternoon/evening. NW winds G30-35+KT probable Sunday afternoon/night. .Monday...Most likely VFR, low chance of MVFR in any snow showers. NW winds G25-35KT possible. && .MARINE... High pressure builds over the coastal waters today with sub SCA conditions with lowering seas and winds. A weak frontal system moves through the waters Thursday night and Friday with sub SCA conditions continuing. Tranquil conditions continue over the waters through the day on Saturday before an approaching low results in deteriorating conditions Saturday night. SCA conditions are expected to develop beginning Saturday night and continue through the day on Monday, with gale force gusts on the ocean water and potentially the near shore waters Sunday afternoon into Monday. Winds should begin to subside below SCA levels Monday night, but ocean seas may remain elevated. && .HYDROLOGY... For Thursday night into Friday morning light precipitation is expected with liquid amounts under a quarter inch. Two to three inches of liquid equivalent precipitation is likely Saturday night through the day on Sunday. Frozen precipitation may be predominate across the interior. Liquid rain is probable closer to the coast Sunday morning into early Sunday afternoon where minor urban and poor drainage flooding is possible in any periods of heavier rain. && .TIDES/COASTAL FLOODING... Minor to locally moderate coastal flood impacts are possible during the Sunday morning high tide cycle. Departures of one to one and a half feet, locally two feet, are needed for minor benchmarks to be reached and two and a half to three feet are needed for moderate benchmarks to be reached. && .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...None. && $$ SYNOPSIS...JE/DS NEAR TERM...BC/JE SHORT TERM...JE LONG TERM...DS AVIATION...Maloit/DS MARINE...JE/DS HYDROLOGY...JE/DS TIDES/COASTAL FLOODING... EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.