Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 202154 AFDOKX Area Forecast Discussion National Weather Service New York NY 554 PM EDT Tue Mar 20 2018 .SYNOPSIS... A major winter storm will impact the tri-state area Wednesday into Wednesday night as a deepening coastal low moves off the Mid Atlantic coast to south and east of Long Island. High pressure builds in from southeast Canada through the weekend. Another storm system may pass to our south late in the weekend. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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The first of two coastal lows will pass to the south and east of the area this evening. A confluent flow aloft and a polar high to the north will keep the area primarily dry with a light wintry mix possibly along the coast early this evening before conditions dry out. The main focus of concern then shifts to an upper low over the Tennessee and Ohio Valleys that translates east tonight ahead of a northern branch shortwave trough moving into the upper Great Lakes. The latter feature will maintain a downstream polar high across eastern Canada with an anomalously cold airmass in place for the start of the spring. At the same time, a second coastal low will take shape off the Mid Atlantic coast overnight in response to the forcing from the approaching upper low. It is this storm that will bring snow into the region toward daybreak along the coast, which will be the start of what appears to be the potential for one of the biggest March snowfalls recorded at Central Park since 1960. As for temperatures, lows will range from the upper 20s across the interior to the lower 30s at the coast. This is nearly seasonable due to the insulating affect of the cloud cover.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Snow will overspread the area from the coast into the interior during the morning hours becoming heavy with snowfall rates of 1 to 2 inches an hour in the afternoon. This could possibly move in as early as late morning at the coast. As for the guidance, since the 06Z run there has been a shift to the southeast with the axis of heaviest precipitation, which now appears to be from NYC northeast across Long Island and southern Connecticut. This area has liquid equivalent amounts around 1.5 inches, with lesser amount to the NW. Much of the area by the time the event ends Wednesday night will receive between 10 to 16 inches of snowfall with localized higher amounts. Briefly, there could be a mix with sleet at the coast in the morning. Unlike previous storms, this airmass is colder and drier and with the onset of the moderate to heavy snowfall, temperatures will likely remain at or below freezing for much of the event. Thus, expect a higher snowfall ratio, closer to 10:1 or even higher. There is some uncertainty with the ECMWF solution pointing to lower liquid equivalent amounts, but it appears to be an outlier from the respect of a weaker closed low off the New England coast by Wednesday night. The exact placement of the heavy snow band is also a difficult thing to pinpoint, but a well defined deformation zone and frontogenesis to the NW of the low track points to this signal. The winds will be gusty throughout the day on Wednesday, with the strongest gusts across coastal Connecticut and coastal Long Island. The winds will gust up to 30 mph across New York City, and 35 to 45 mph across coastal sections of Connecticut and Long Island. This will result in periods of near-blizzard conditions. && .LONG TERM /THURSDAY THROUGH TUESDAY/... The coastal storm will continue to pull away from the area Thursday. There will be some lingering snow showers, mainly for Long Island and southeastern Connecticut in the morning, with only minor additional accumulations possible. Winds will diminish as well as the pressure gradient relaxes, though it will still be rather breezy Otherwise, dry conditions should return for Thursday afternoon as high pressure builds in from southeastern Canada. Strong high pressure continues building in at the surface through the weekend. Upper level low moves through on Friday. Little moisture to work with, with only weak lift noted, so any light precipitation looks unlikely, but a passing shower or flurry cannot be ruled out just yet. Low pressure over the Mid-West will move east late Saturday into Sunday. With strong surface high pressure building south from southeastern Canada, it will suppress the storm to the south, ejecting off the Mid-Atlantic/Southeast US coast on Sunday. An upper level trough/upper level low coupled with weak surface troughing may provide more in the way of lift for some snow showers or flurries. The storm system that ejects off the coast is forecast to stall out over the Western Atlantic through the middle of next week, while surface high pressure gets squeezed between the offshore low and another approaching storm system to the west, with ridging aloft. && .AVIATION /22Z TUESDAY THROUGH SUNDAY/... Winter Storm to Impact Terminals Wednesday into Wednesday night... High pressure gives way to a strong low pressure area developing off the Mid-Atlantic Coast that will pass southeast of Long Island Wednesday through Wednesday night. VFR lasts through much of tonight but with gradually lowering and thickening clouds. A light wintry mix will transition to a steady snow Wednesday morning through the rest of the TAF period, which will be heavy at times, especially in the afternoon. Expect mainly IFR to LIFR conditions Wednesday with VLIFR at times, especially in the afternoon. Accumulations of snow will vary from near 10 to 15 inches, lower for KSWF. Snowfall rates of 1 to 3 inches per hour possible mid to late morning and continue in the late evening. Isolated thunder possible during this time as well. ENE flow 10-15 kt gusting to 20 kt continues into tonight. Winds become more N/NE 15-20 kt Wednesday and gust 25-30kt with peak gusts 35-40 kt possible. The bulk of the snow is Wednesday through Wednesday evening. Total forecast snow accumulations in inches: KBDR/KGON/KEWR/KTEB/KJFK/KLGA/KHPN/KISP: 10-15 Snowfall rates of 1 to 3 inches per hour possible mid to late morning and continuing in the late evening. KSWF: 6-10 NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: Gusts could be more intermittent into tonight. MVFR/IFR possible 08-10Z. KLGA TAF Comments: Gusts could be more intermittent into tonight. MVFR/IFR possible 08-10Z. KEWR TAF Comments: Gusts could be more intermittent into tonight. MVFR/IFR possible 08-10Z. KTEB TAF Comments: Gusts could be more intermittent into tonight. MVFR/IFR possible 08-10Z. KHPN TAF Comments: Gusts could be more intermittent into tonight. MVFR/IFR possible 08-10Z. KISP TAF Comments: Gusts could be more intermittent into tonight. MVFR/IFR possible 08-10Z. .OUTLOOK FOR 18Z WEDNESDAY THROUGH SUNDAY... .Wednesday...Heavy snow continues with sub-IFR conditions likely. Snow tapers off overnight. NE winds G20-35KT. .Thursday-Friday...VFR. N winds G20-25KT on Thu. .Saturday...VFR. .Saturday night-Sunday...MVFR possible in chance of rain/snow. && .MARINE... Any Small Craft and Gale conditions will yield to Storm conditions on the ocean waters overnight and last through Wednesday. Gale conditions will prevail by early Wednesday morning for the remaining western waters and prevail through the day on Wednesday. By Wednesday night the Storm conditions will reside only in the eastern ocean waters and last until Thursday morning. Gale conditions will continue for the eastern sound also until Thursday morning. Gusts over the eastern ocean waters may get up to 55 kts during Wednesday and Wednesday night with seas 10 to 15 ft. Waves on the ocean diminish on Thursday, with waves heights in the morning generally from 8-12 ft. Waves fall below 5 ft late Thursday night and remain below SCA criteria through Saturday. Waves build again Saturday night as a storm system passes well south of the coastal waters, allowing for an increase in northeasterly flow. Waves then remain above SCA criteria through the beginning of the new work week as the coastal storm remains over the western Atlantic. Winds also diminish Thursday, coming below 25 kt late Thursday night and then remain below SCA criteria through early Sunday morning. Winds of 25 kt or higher are then possible through Monday morning in response to the offshore coastal storm. && .HYDROLOGY... A significant precipitation event will impact the area Wednesday into Wednesday night with liquid equivalent amounts from 0.75 to 1.50 inches, highest from NYC and points east. This will fall mainly as snow, so no hydrologic impact expected. && .TIDES/COASTAL FLOODING...
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Prolonged NE-N flow will push water levels up Tue night into Wed night. Departures of about 2-3 ft for moderate flooding, and 1-1.5 ft are needed for minor flooding for many locations. Just localized minor impacts expected with tonight`s high tide cycle as NE winds are just beginning to ramp up top gale. With NE gale to storm force winds going into the late Wednesday morning/early afternoon high tide cycle, widespread minor to moderate impacts are likely for the Wed late morning/early afternoon high tide. Previous forecasts headlines for Wed continue to fit the latest guidance so no changes needed. Values for the north shore and bays of eastern Long Island were increased where winds will be strongest and wave action will cause additional runup. Another round of minor to locally moderate coastal flooding likely for the Wed night high tide cycle. Have issued a coastal flood watch for the south shore bays of NYC and western Long Island where impacts appear to be the greatest. There is a bit of uncertainty and would need to see how the guidance is doing once the NE fetch becomes established tonight and Wed so have not extended the advsy into Wed night at this time. Winds will also be shifting to the N Wed aftn which will halter the tidal piling with some drainage occurring. Will have to continue to monitor this tidal cycle, as guidance typically has a low bias on the back end of multiple-cycle surge events.
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&& .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...Winter Storm Warning from 6 AM Wednesday to 6 AM EDT Thursday for CTZ005>012. Coastal Flood Advisory from noon to 6 PM EDT Wednesday for CTZ009-010. NY...Winter Storm Warning from 6 AM Wednesday to 6 AM EDT Thursday for NYZ067>075-078>081-176>179. Coastal Flood Advisory from noon to 6 PM EDT Wednesday for NYZ071-078-079-081-177. Coastal Flood Advisory from 10 AM to 2 PM EDT Wednesday for NYZ074-075-178. Coastal Flood Warning from 9 AM to 3 PM EDT Wednesday for NYZ080-179. Coastal Flood Watch from Wednesday evening through late Wednesday night for NYZ075-080-178-179. NJ...Winter Storm Warning from 6 AM Wednesday to 6 AM EDT Thursday for NJZ002-004-006-103>108. Coastal Flood Advisory from 10 AM to 2 PM EDT Wednesday for NJZ006-106-108. MARINE...Gale Warning from 2 AM Wednesday to 6 AM EDT Thursday for ANZ330-340-345. Gale Warning from 6 AM to 8 PM EDT Wednesday for ANZ335-338. Storm Warning from 2 AM to 8 PM EDT Wednesday for ANZ355. Storm Warning from 2 AM Wednesday to 6 AM EDT Thursday for ANZ350-353. && $$ SYNOPSIS...JP/DW NEAR TERM...DW SHORT TERM...JE/DW LONG TERM...JP AVIATION...NV MARINE...JE/JP HYDROLOGY...JP/DW TIDES/COASTAL FLOODING... EQUIPMENT... is the U.S. government's official web portal to all federal, state and local government web resources and services.