Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 181424 AFDOKX Area Forecast Discussion National Weather Service New York NY 924 AM EST Fri Jan 18 2019 .SYNOPSIS... A weak area of low pressure passes to the south, followed by another to the north later today. A cold front will cross the area tonight. 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 Wednesday and moves across the region on Thursday. && .NEAR TERM /THROUGH TONIGHT/... Any lingering light snow has tapered off. Temps warm through the day as pesky clouds hang on through much of the day. Highs will approach or reach 40. A weak area of low pres will pass to the N resulting in the passage of a weak warm front into early this afternoon. A cold front then passes this evening. Lows tonight drop into the 20s area wide with partially clearing skies. && .SHORT TERM /SATURDAY/... High pressure nosing in from the north will shift east on Sat with an easterly wind flow developing and low pres moving from the mid Mississippi Valley into the Ohio Valley. Overrunning pcpn well out ahead of the center of the storm could begin to move into western portions of the forecast area as early as mid to late aftn, but more likely during the late aftn/early eve hours. Thermal profiles support snow across the entire Tri State Area into the evening. High on Sat will generally range in the lower to mid 30s, although the normally colder spots across the interior could struggle to get out of the 20s. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... A significant winter storm will impact the Tri-State area Saturday night into Sunday with the coldest air of the season Sunday night into Monday. A winter storm watch remains in effect for much of the region late Saturday into Sunday. Models have slowly come into better agreement over the last 24 hours, but there still remains a good deal of uncertainty regarding the exact track, thermal profiles, and precipitation types and amounts for the winter storm. The southern stream energy with this system is now over the western US, so continued RAOB sampling should help establish better agreement today. However, changes in track forecast are still possible. High confidence remains on this storm being a high liquid equivalent event. Strong warm advection will be underway Saturday night with snow increasing in intensity across the entire region. A corridor of intense 850-700 mb frontogenesis will move across from 00z Sunday through 12z Sunday ahead of a broad middle level low. Strong southerly low level winds will likely bring a tight thermal gradient and warm nose from south to north through the night. Snow will change to a wintry mix at the coast around midnight and then across much of the interior by Sunday morning. Much of Long Island, NYC, and southeast Connecticut should change to plain rain early Sunday morning, but the interior may see a mix of sleet and freezing rain. The depth of the low level cold on the NAM and NAM 3-km is quite impressive, which may cut down on the freezing rain somewhat and bring more sleet once the changeover occurs. This may also mean a greater chance for freezing rain closer to the coast. Confidence in this scenario is still low, so will continue to show a general sleet and freezing rain mix across the interior once the warm nose moves in aloft. Surface temperatures are also uncertain and dependent on how much cold air damming occurs. There is a high amount of spread from temperatures barely rising above freezing even at the coast to warming well into the 40s. All of this will ultimately depend on the track of the low. If the low tracks just south of the region, then a colder profile with potential for more ice at the coast would be realized. If the low track is further north and over portions of the region, then warmer air would likely occur with less ice. The low shifts east of the region on Sunday morning into Sunday afternoon. Once the low passes east, winds will shift to the north and north west with a rapid cooling occurring both at the surface and aloft. There has been a trend in the models for less precip on the back side of the low, so there may be limited amount of frozen precipitation as the storm pulls away Sunday afternoon. As temperatures fall below freezing late Sunday morning into Sunday afternoon, any standing water on untreated surfaces could quickly freeze, creating hazardous travel conditions even where little wintry precipitation occurs. Highest snow/sleet accumulations are expected mainly NW of NYC where mostly 4 to 8 inches is currently forecast, and possibly even higher towards Putnam and Orange Counties. Most other areas are expected to see less than 6 inches of snow/sleet, however with the potential of at up to around a tenth or two of ice accretion in addition to snow/sleet, hazardous conditions are possible for these locations as well. The only areas not under a watch are parts of Long Island where 1-3 inches of snow/sleet is expected and maybe at least a trace of ice could occur. Some of the watch across coastal locations and possibly NYC may eventually be converted to an advisory depending on the forecast trends. Temperatures continue to plummet as arctic air advects into the region behind the storm. Lows Monday morning will generally be in the single digits. There is a possibility of a few locations in interior falling to near 0, especially with a new snow/sleet pack. Gusty northwest winds will result in wind chills around 10 to around 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. Timing and thermal profiles with this next system are uncertain due to model disagreement. Precip chances are in the forecast late Wednesday into Wednesday night. The primary low tracks up into southeast Canada, so the majority of the precip should be liquid with warmer air ahead of the system. Precip may also occur on Thursday depending on if low pressure develops along the front. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... One weak low pressure system passes to the south and east of Long Island while another low passes well to the north through early this afternoon. High pressure briefly builds in this afternoon into tonight. A deeper low approaches from the southwest toward 12Z Saturday. Any lingering light snow ends with conditions continuing to vary, mainly IFR, and at times MVFR. Ceilings will take some time to lift, remaining IFR to low MVFR into the early afternoon. MVFR ceilings likely linger until early this evening, when conditions improve to VFR. Winds light NE, become light southerly around midday, then W-NW this evening and tonight. ...NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Amendments likely with timing and durations of IFR uncertain. The afternoon KJFK haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KLGA TAF Comments: Amendments likely with timing and durations of IFR uncertain. The afternoon KLGA haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KEWR TAF Comments: Amendments likely with timing and durations of IFR uncertain. The afternoon KEWR haze potential forecast is GREEN, which implies slant range visibility P6SM outside of cloud. KTEB TAF Comments: Amendments likely with timing and durations of IFR uncertain. KHPN TAF Comments: Amendments likely with timing and durations of IFR uncertain. KISP TAF Comments: Amendments likely with timing and durations of IFR uncertain. .OUTLOOK FOR 12Z SATURDAY THROUGH MONDAY... ***HIGH IMPACT WEATHER SATURDAY NIGHT INTO SUNDAY NIGHT*** .Saturday...VFR AM, then snow with IFR vsby developing in the afternoon, especially from the NYC metros north/west. .Saturday night...IFR or lower conds throughout. Snow changing to rain after midnight at NYC/Long Island terminals, and to a wintry mix at northern terminals. LLWS likely NYC metro/coastal terminals. .Sunday and Sunday night...IFR or lower likely. Rain from metro New Jersey, into NYC, and Long Island, and along the Connecticut coast, with a wintry mix continuing inland, in the morning. The precipitation transitions back to snow and a wintry mix, before ending early Sunday evening, then becoming VFR. LLWS possible in the morning. N-NW winds G25-35kt and flash freeze likely in the afternoon. .Monday-Monday night...VFR. NW winds G25-35KT, G25kt in the evening. .Tuesday...VFR. && .MARINE... Sub-advsy conds are expected through Sat although an increasing easterly flow will be developing Sat aftn. SCA conditions are expected to develop beginning Saturday night. Gale force gusts on the waters east of Fire Island inlet, eastern LI Bays, and eastern LI sound Saturday night. A gale watch is now in effect for this time period. Gusty winds will continue into Sunday into Monday with the possibility of gales on the ocean waters 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. Sub-SCA conditions return on Tuesday. && .HYDROLOGY... One and a half to around two 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 late Saturday night into 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...Winter Storm Watch from Saturday afternoon through Sunday afternoon for CTZ005>012. NY...Winter Storm Watch from Saturday afternoon through Sunday afternoon for NYZ067>075-078-176>179. NJ...Winter Storm Watch from Saturday afternoon through Sunday afternoon for NJZ002-004-006-103>108. MARINE...Gale Watch from Saturday evening through late Saturday night for ANZ330-340-350-353. && $$ Update...PW

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