Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 152034 AFDOKX Area Forecast Discussion National Weather Service New York NY 334 PM EST Sat Dec 15 2018 .SYNOPSIS... A series of weak low pressure systems pass to the south of the area through the weekend while high pressure remains centered to the north. Low pressure departs to the northeast Monday as a Canadian cold front passes through the area. High pressure builds mid week. Low pressure tracks to the west late in the week, as a warm front passes. && .NEAR TERM /THROUGH SUNDAY/... Primary concern into tomorrow is the potential for freezing rain to develop across far northern NJ, the lower Hudson Valley and portions of western Connecticut. Cold air damming at the surface as the high builds to our north will allow temperatures to lower to right around freezing in these areas. Coincidentally as the upper low nears, low level warm advection will strengthen in strong easterly flow above the surface, allowing a warm layer to develop between around 875-600 mb. As always, there is significant uncertainty regarding the extent of cold air damming, but it is typical for model forecasts to underdo the cold air, and then erode it too fast once established. Trended on the colder side, more towards the operational NAM, on temperatures, keeping things near freezing through much of the day where a Winter Weather Advisory is now in effect. The Cooperative Institute for Precipitation Systems (CIPS) historical analogs reflect high probabilities for freezing rain across the aforementioned areas, lending some confidence towards a colder surface solution. It is possible that freezing rain continues well into the afternoon. There are certainly two potential scenarios in which the forecast could develop differently as well: 1. The colder/below freezing solution does not materialize, and while a cold rain falls, freezing upon contact at the surface does not occur. 2. As the upper low passes, colder temperatures aloft lead to weak elevated instability, which may locally enhance precipitation rates and even mix a bit of graupel in with the freezing rain. If instability can develop, ice accumulations may be greater than the 0.10-0.25 inch currently forecast for the advisory areas. Outside the advisory, confidence is low in both temperatures and the expected amount of ice. A Special Weather Statement is in effect highlighting the potential for ice in those periphery areas, and should forecast/model solutions trend colder, then an advisory may be needed. Elsewhere, a cloudy rainy day is expected as the upper trough finally moves over the area, with the main concern being breezy conditions that will develop overnight and persist into Sunday. Temperatures will range from 5 to 10 degrees below climatological normals. && .SHORT TERM /SUNDAY NIGHT/... The upper low and an attendant coastal low quickly depart to the northeast Sunday night in advance of a long wave trough, allowing a cold front to move through the area. Any ongoing precipitation may transition to snow as cold advection strengthens, with quick but minimal accumulations primarily to the north and west of the NYC area. Breezy conditions continue behind the front, combining with lowering temperatures to make it feel as though it is in the 20s overnight. Across the interior - have extended the Winter Weather Advisory into Sunday night to account for these additional potential accumulations. && .LONG TERM /MONDAY THROUGH SATURDAY/... Aloft, vigorous upper shortwave dives out of eastern Canada, quickly passing across the northeast Monday into Tuesday. Ridge quickly builds in for mid week. Next shortwave energy out of central Canada will result in deepening longwave trough across the mid portion of the country Thursday. This trough pivots east before lifting northeast into eastern Canada by next weekend. At the sfc, reasonable model agreement noted as deepening low pressure moves northeast toward the Canadian Maritimes Monday. A cold front passes late in the day. High pressure then builds Tuesday and Wednesday. By Thursday, low pressure develops over the Tennessee valley, deepens and moves north across the Great Lakes region Friday into Saturday. A warm front likely sweeps north Friday, followed by a series of troughs Saturday. As for sensible weather, any light wintry mix precip ends early Monday morning. Do not foresee much precip with the upper shortwave and associated cold front later Monday other than perhaps some flurries. However, appears there is too much dry air to overcome. Dry weather persists mid week thanks to ridging and associated subsidence, then rain chances increase Thursday as deep southerly flow and WAA commence, enhancing lift. Steadier rain likely impacts the area Thursday night into early Friday based on timing from 12Z model suite, with mid level drying likely lowering coverage Friday afternoon through Saturday. Near normal temps Monday will fall below seasonable Monday night and Tuesday due to CAA behind the front. This will be short lived as ridge builds, followed by deep south flow ahead of amplifying trough to the west. Temps rise back to above normal Thursday-Saturday. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... A series of lows track to the south of Long Island into Sunday afternoon, as high pressure builds in to the north. Primarily VFR with periods of MVFR this afternoon/evening, with MVFR/IFR developing again tonight, most likely towards/after midnight. VLIFR is possible Sunday morning with any locally heavy rainfall. Freezing Rain is likely at KSWF from around 8-16Z Sunday, with a low chance it lingers into early Sunday afternoon. Light and variable winds become N/NE into the afternoon. Winds gradually increase this evening into the overnight period with sustained winds of around 10-20KT - highest near the coast. LLWS is probable Sunday morning for all but KSWF with winds at around 2000 ft at 35-50KT (strongest near Long Island S coast). .OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY... .Sunday afternoon-night...MVFR/IFR in rain likely, possibly starting as FZRA at KSWF early Sunday afternoon. Potential for wintry mix across interior terminals Sunday Night, as precipitation tapers off, then becoming VFR late. E-NE winds 20-30KT possible eastern terminals Sunday afternoon. NE-N winds G20-30kt possible eastern terminals Sunday night. .Monday-Monday night...VFR. NW winds G20-30KT probable. .Tuesday-Wednesday night...VFR. NW Wind G15-20kt possible Tuesday, W- WSW winds G15-20KT possible Wednesday. .Thursday...VFR, possibly becoming MVFR or lower late with rain. LLWS possible late. && .MARINE... East-Northeast winds and gusts quickly increase tonight into Sunday as low pressure deepens along the coast and high pressure remains to the north. The strongest low-level winds are expected into Sunday afternoon, where there is potential for isolated storm-force winds to mix to the waters. A gale warning is now in effect for all waters. Although winds decrease somewhat Sunday night as the low passes along the coast, it is likely SCA-level winds will continue, and seas will remain elevated on the ocean waters. Winds then temporarily diminish early Monday as the low departs to the Canadian Maritimes. A cold front passes across the waters late Monday, and winds increase once again Monday night into Tuesday. In fact, gale force winds are possible once again. Winds will diminish Tuesday night through Wednesday as high pressure builds. Winds shift around to the S/SE Thursday, and will increase late in the day ahead of deepening low pressure to the west. Rough seas Monday and Tuesday are expected to subside mid week as the winds diminish. Seas build late Thursday and Thursday night. && .HYDROLOGY... Between 0.50" and 1.25" of rainfall is then expected late tonight through Sunday night. The highest rainfall amounts are currently expected across portions of northeastern New Jersey, NYC, and Long Island. A period of moderate to heavy rainfall will be possible Sunday morning. Low chances of minor nuisance/poor drainage flooding will be possible during the daytime on Sunday. Next chance for significant rainfall of at least a half an inch will be late in the week. Too early to determine if there will be any hydrologic concerns with this potential late week event. && .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...Winter Weather Advisory from midnight tonight to 6 AM EST Monday for NYZ067-068. NJ...Winter Weather Advisory from midnight tonight to 6 AM EST Monday for NJZ002. MARINE...Gale Warning until midnight EST Sunday night for ANZ330-335- 338-340-345-350-353-355. && $$ SYNOPSIS...MD/PW NEAR TERM...MD SHORT TERM...MD LONG TERM...PW AVIATION...Maloit MARINE...MD/PW HYDROLOGY...MD/PW EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.