Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 181440 AFDOKX Area Forecast Discussion National Weather Service New York NY 940 AM EST Sun Feb 18 2018 .SYNOPSIS... High pressure builds over the area today, then slides offshore into Monday. A warm front slowly approaches from the south into Monday night, then lifts to the north early on Tuesday. A cold front then approaches from the west into Wednesday, then sinks to the south Wednesday evening. This front then stalls to the south with waves of low pressure riding along it through the end of next week, as high pressure builds across southeastern Canada. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Forecast on track with just some minor adjustments to reflect latest observations. Otherwise, Northern stream ridging builds in today behind a northern stream trough passing off to the ENE. Expect sunny skies today. Undercut guidance a bit on highs today, with some of the solar energy going towards melting last night`s snowfall. Highs should be slightly above normal as a result.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Given expected snow melt today, and temperatures falling below freezing tonight across the Lower Hudson Valley, S CT, most of NE NJ (except areas adjacent to NYC) and most of Suffolk County, there is the potential for black ice tonight on untreated surfaces. Will address this threat in the HWO. Deep layered ridging, centered off the Florida coast, builds in tonight and Monday. Tonight will be clear and dry as a result. Increasing low level warm advection on Monday will result in increasing cloud cover and a chance for some rain building into the area mainly Monday afternoon (best chance over far W zones where have low end likely pops). Lows tonight should run around 5 degrees below normal and highs on Monday around 5 degrees above normal, mainly in the mid-upper 40s, except lower 40s in the higher elevations to the N/W of NYC. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... A deep layered ridge whose center progresses NW to off the SE seaboard through the middle of the week will be the main weather player through then. Continued low level warm advection Monday night into Tuesday will likely bring rain to the region Monday evening, with pops decreasing through the night as the 850 hPa warm front lifts to the NE. Could see some patchy fog late Monday night over the Lower Hudson Valley as a result of abundant low level moisture trapped in local valleys. The surface warm front lifts to the north Tuesday morning, bringing the end to any lingering threat of light rain to the region. A passing shortwave Tuesday night over the top of the ridge could bring some isolated showers (maybe even some patchy drizzle - but not quite confident enough to forecast this yet) to the area. Could also see patchy fog yet again over the Lower Hudson Valley. The region should be mainly dry on Wednesday as a 700 hPa shortwave undercuts the ridge - however should see some mid- level cloud cover as a result - and a slight chance of a shower over far NW zones. Temperatures Tuesday and Wednesday will be well above normal across the region. Highs Tuesday ranging from around 10 degrees above normal over Log Island/coastal CT and coastal NYC where cooler waters near by will serve as a limiting factor to around 20 degrees above normal inland. Depending on how much cloud cover there is on Wednesday, it could be even warmer than Tuesday, with highs possibly around record levels. Refer to the climate section of the AFD for details. A passing northern stream shortwave flattens the ridge Wednesday night, allowing a cold font to sink to the S, with some passing showers. The forecast becomes somewhat tricky for the remainder of next week as it becomes dependent on how for to the S the cold front sinks, which depends on the strength of high pressure building across SE Canada. Noting that the GFS typically does not handle a pattern like this well, leaned towards the ECMWF and CMC Global for the remainder of the forecast. As a result, expect unsettled weather during this time frame, with periods of off and on precipitation - with exact timing determined by the passing of shortwaves embedded in the flow aloft (very hard to predict this far out). As a result, have limited pops to at most chance Thursday-Saturday. Also with near seasonal temperatures returning on Thursday-Friday, have the potential for some wintry precipitation across mainly northern interior zones as well (for now going with mainly a mix of rain and snow there). For now it appears that Saturday could end up being a bit warmer than Thursday and Friday, so no wintry mix then. This is all still highly uncertain and there is the potential for temperatures to end up a bit colder Thursday-Saturday then currently forecast. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/...
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High pressure builds in through this evening, then moves offshore tonight. VFR. NW winds with gusts 20-25KT bcmg WNW this aftn with gusts ending. Winds favor north of 310 magnetic until around noon then favor south of it thereafter. Light and vrb winds tonight. .OUTLOOK FOR 12Z MONDAY THROUGH THURSDAY... .Mon...Becoming MVFR to IFR in rain and possibly fog Monday afternoon/night. .Tue...MVFR or IFR possible in the morning and again at night, otherwise VFR with SW wind G20KT possible. .Wed...VFR. Chance of showers with MVFR. .Thu...MVFR in rain.
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&& .MARINE... Made minor changes this update to reflect the latest trends in observations and guidance. The forecast appears on track. NW winds increase this morning behind the departing low and high pres building from the west. There will be about a 6 hr period of gusts reaching SCA levels on the ocean waters as well as eastern LI Sound and Peconic/Gardiners bays. Have added the latter to the advsy and also extended the time from 09z to 18z to 1-2 hours of padding on each side. Seas on the ocean may briefly reach marginal advsy levels as well. Sub-advsy conds are expected on all waters through Tue. A moderate SW flow on the ocean waters Tue night into Wed night may result in advsy level seas on the ocean waters. An strong sfc inversion should keep gusts below criteria. A cold front moves through Wed night with winds becoming northerly and sub-advsy conds returning through the remainder of the period. && .HYDROLOGY... Even with the snow expected to melt rapidly, given less than 1 inch of liquid water equivalent in the snow, and no widespread heavy rainfall to couple with the snow melt, no significant hydrologic impacts are expected through at least the middle of this week. && .CLIMATE... Record Highs for Wednesday February 21, 2018 Location........Record/Year....Forecast High Newark..............69/1953.........72...... Bridgeport..........59/2002.........63...... Central Park........68/1930.........70...... LaGuardia...........68/1953.........69...... J F Kennedy.........63/2002.........65...... Islip...............63/2002.........62...... && .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 1 PM EST this afternoon for ANZ330- 340-350-353-355. && $$ SYNOPSIS...Maloit NEAR TERM...BC/Maloit SHORT TERM...Maloit LONG TERM...Maloit AVIATION...JC/24 MARINE...24/Maloit HYDROLOGY...Maloit CLIMATE... EQUIPMENT...

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