Area Forecast Discussion
Issued by NWS Upton, NY

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541 FXUS61 KOKX 180002 AFDOKX Area Forecast Discussion National Weather Service New York NY 802 PM EDT Sat Mar 17 2018 .SYNOPSIS... A cold fronts cross the region this evening, followed by another cold front pushing through the area Sunday night. High pressure then builds down from southern Canada through Monday night. A coastal low tracks to the south then southeast of Long Island from Tuesday through Wednesday night. High pressure builds down from central Canada for the remainder of next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Made minor changes this update to reflect the latest trends in observations and guidance. The forecast appears on track. A shortwave mid level troughs will move across the area this evening. No precipitation is expected with this wave due to dry low levels. However, do expect a re-enforcing shot of cold air. Lows tonight will fall into the 20s, with teens inland and in the Long Island Pine Barrens. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday will be mostly sunny with highs in the upper 30s and lower 40s. Another shortwave will pass to our north, except this time, it will be accompanied by a weak surface low that looks to have more available low level moisture and lift, so expect some evening flurries north and east of NYC. Lows Sunday night will fall into the 20s and lower 30s. && .LONG TERM /MONDAY THROUGH SATURDAY/... There are 4 main players that will impact how the weather will play out over the region from Monday into Thursday: 1) The rather large cutoff low currently over SE Canada 2) The cutoff low currently over the Pacific NW (including the lobe that stretches offshore and is not fully sampled by the radiosonde network) 3) the ridging between the two systems and 4) the cutoff low currently over the Gulf of Alaska. The models have come into better general agreement in the evolution of the first feature, maintaining it to the N through Monday, then lifting it to the NE into the middle of the week - with some question if another cutoff low replaces the initial one over SE Quebec. They still differ over the handling of the PAC NW system - both in terms of how many pieces of energy break off from it and head east from the Rockies and how rapidly they do so. Because of the differences in the timing/amount/strength of energy ejecting from the PAC NW cutoff there are differences in the ridging between the two cutoff lows. The models are fairly similar in handling the Gulf of Alaska system, bringing it S and serving as an anchor of sorts for the PAC NW Cutoff as it eventually opens into a trough by midweek. The GFS has an additional issue in that its initial coastal low ends up S of the 700 and 500 hPa shortwave trough that supports it. This rarely happens - so suspect the surface low is probably a bit farther N/E of where the GFS has it from Tuesday afternoon into Wednesday. Given the spread in model solutions have opted to go with a blend of the 12Z ECMWF/CMC/NAM/GFS (with surface low and precip shield modified accordingly based on above). So expect a coastal low to track to the south then southeast of Long Island from Tuesday through Wednesday night (possibly 2 lows depending on exact evolution of ejecting PAC NW energy). As a result, go dry Monday/Monday night (potentially under shortwave ridging that starts out in between the two cutoff lows depending on exact timing/nature of energy ejecting from the PAC NW cutoff). Then increase pops on Tuesday to slight chance over mainly Lower Hudson Valley and SW CT and low end chance elsewhere, and continue with pops like this through Wednesday night. With a shift in the average low track farther S, did make the area mainly snow for this event (consistent with using surface wetbulb temperature as a rough proxy for the rain/snow line this far out). For now it appears that any coastal low should be to far SE/E on Thursday to have any impact on the region in terms of precipitation, so have gone dry on Thursday. One thing that is fairly consistent regardless of solution is that it will be at least breezy to windy over the region from late Tuesday into Thursday - potentially rather gusty depending on exact track/strength of the coastal low(s). The axis of the SE Canada cutoff passes to the east Thursday night, but with dry low levels, it should be dry. Friday and Friday night should be dry as northern stream ridging transits the area. For now went dry on Saturday as a cutoff low builds to the north but it appears (other than in 12z ECMWF) that the next batch of moisture/lift holds off until later in the weekend. Temperatures are forecast to be below normal Monday-Saturday. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... A weak cold front or trough passes through the terminals this evening followed by high pressure building to the north into Sunday. A weak wave of low pressure is then forecast to pass to the SW of the area late Sun/Sun eve. VFR and dry weather thru the period. W-NW winds 10-15 kt with an ocnl gust up to 20 kt through 02z, shifting to the NW-N 5-10kt behind weak front overnight. Sunday NW winds increase 10-15 kt. There may be an occasional gust up to 20 kt generally between 15z and 22z. .OUTLOOK FOR 00Z MONDAY THROUGH THURSDAY... .Sunday night-Monday night...VFR. .Tuesday...VFR, with a low chance of MVFR or lower by the afternoon in snow, or wintry mix along the coast. Gusty NE flow develops, 15-25kt. .Tuesday night and Wednesday...Low chance of MVFR or IFR in snow. Gusty NE wind 15-25kt. .Thursday...VFR. Gusty N wind 10-20kt. && .MARINE... Allowed the Small Craft Advisory (SCA) to expire for western/central waters, with one remaining in effect until midnight for eastern waters. Once the winds and seas fall, expected quiet conditions Sunday and Sunday night, although a few wind gusts may approach 25 kt on the eastern ocean waters during the daytime Sunday. A relatively relaxed pressure gradient over the waters Monday and Monday night will limit winds to 15 kt or less, with seas below SCA levels as well. The pressure gradient should tighten Tuesday and remain moderate to strong in strength into Thursday. SCA conditions probably develop on the coastal ocean waters Tuesday and on the remainder of the waters Tuesday night. SCA conditions probably will continue into at least Wednesday night, with Gale conditions possible, most likely on coastal ocean waters, Tuesday night and Wednesday. Conditions should gradually fall below SCA levels on Thursday. && .HYDROLOGY... It should be dry through Monday night. A low probability for significant precipitation exists Tuesday through Wednesday night depending on the eventual track of low pressure centers. If precipitation does indeed occur, it likely will be in the form of snow, so no hydrologic impacts are anticipated. && .TIDES/COASTAL FLOODING... There is the potential for a prolonged period of E-NE flow from Monday night into Wednesday Night. Tidal departures of generally only 1 to 1 1/2 ft are needed for minor flooding for many locations during this time, and 2 to 3 ft for moderate. Depending on the exact track/strength of a coastal low or lows during this time frame, there is the potential for minor to moderate coastal flooding, but predictability on the details remains low. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) is off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ330-340- 350. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.