Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 250126 AFDOKX Area Forecast Discussion National Weather Service New York NY 926 PM EDT Thu May 24 2018 .SYNOPSIS... A back door cold front lingering southeast Connecticut and eastern Long Island will gradually dissipate overnight as high pressure otherwise dominates. A weak low pressure trough will develop over western portions of the region on Saturday. Another back door cold front will pass through Saturday night into Sunday morning, becoming nearly stationary just to the south and west through Memorial Day. Another cold front will follow from the west on Tuesday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Fog/low cloud bank continues to extend over portions of SE coastal CT and along the south fork of Long Island on the cool side of the back door front. This bank is showing signs of shrinking late this evening. The fog bank is aided by onshore flow and evening cooling, but should dissipate overnight as SW flow strengthens. Otherwise, clear skies prevail. Lows tonight will be in the lower/mid 60s in/near NYC, with 50s elsewhere. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... A flat upper ridge will dominate aloft, with offshore sfc high pressure and a week inland trough. With H8 temps increasing to near 15C and H5-10 thicknesses near 570 dm, expect a very warm day, with highs reaching 90 in NE NJ and in the valleys well NW of NYC, with mid/upper 80s elsewhere away from south facing shores. With a very dry air mass in place, heat index values will actually be several deg lower than air temps. Lows Fri night should be near 70 in NYC and in the 60s elsewhere. && .LONG TERM /SATURDAY THROUGH THURSDAY/... A polar low over Greenland and associated trough across SE Canada will slowly slide east through the weekend, while Bermuda ridging builds off the SE coast. The local region will be in between these two features, with broad but weak northern stream shortwave energy over the US/Canadian plains gradually sliding/shearing east towards the NE US through the weekend, as well as vort energy rotating around the Bermuda ridge. At the surface, lee trough development is expected on Saturday. A modestly unstable and sheared environment, with increasing vort energy in the mid/level flow, should lend to afternoon shower/thunderstorm development west of the Hudson River. Main threat will be torrential downpours in increasingly moist airmass, but can`t rule out a few strong to severe storms in this regime as well. Question is timing of trigger. Any convective/shower activity should slide eastward through the late afternoon/evening but weaken overnight with diminishing instability and maritime influence. Temperatures should be quite warm on Saturday with increasing humidity as well. Highs should be well into the 80s away from the south coasts, and upper 70s to around 80 at the coast. Then decent agreement on a backdoor cold front approaching Sat Eve and then pressing across the region Saturday night into Sunday morning. The front, interacting with the sub-tropical environment in place, should increase the coverage of shower activity Sat Night into Sun morning, but thunderstorm activity should decrease after the evening hours as instability diminishes. Locally heavy downpours are the main threat in this environment. The region will then transition to a cooler Canadian maritime airmass on Sunday into Monday, as high pressure builds southward across New England. Subsidence and stable airmass may keep shower/sprinkle activity rather limited by Sun afternoon and continuing through Monday, but stratus will likely hang tough Sunday into at least Monday morning with low-level inversion. Potential for some breaks of sun heading into Monday afternoon as northern/southern stream trough energy begins to slide east. Fairly good agreement on next northern stream shortwave amplifying into Quebec Monday Night into Tuesday, with ridging beginning to build into the region through Midweek. At the surface, a cold front crosses the region Tuesday morning with Canadian high pressure building into the region in its wake. Forcing appears limited with this frontal passage, but some uncertainty on instability, which warrants a low chance for isolated shra/tsra. Otherwise, appears high pressure builds into the region for midweek with dry and near to above seasonable temps. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... High pressure dominates through Friday. Mainly VFR conditions through the TAF period. The only exception is LIFR or IFR conditions in stratus and fog across southeast Connecticut at KGON and the forks of Long Island through around 06z. Conditions should quickly improve to VFR at these locations after 06z. SSW-S winds around 10 kt into this evening at most terminals. Winds will diminish this evening and become light and variable outside of city terminals. SW winds increase to 10-15 kt with gusts 20-25 kt Friday morning into Friday afternoon. ...NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Wind Speeds 10-15 kt through 01z. KLGA TAF Comments: Wind direction may vary between 170 and 220 with speeds 10-15 kt through 01z. KEWR TAF Comments: Wind Speeds 10-15 kt through 01z. KTEB TAF Comments: No unscheduled amendments expected. KHPN TAF Comments: No unscheduled amendments expected. KISP TAF Comments: No unscheduled amendments expected. .OUTLOOK FOR 00Z SATURDAY THROUGH TUESDAY... .Friday Night...VFR. .Saturday...Mainly VFR. Chance of showers and thunderstorms near NYC Metro terminals and to the N and W in the afternoon with possible MVFR. Higher chance of showers and thunderstorms at night. .Sunday-Monday...MVFR or lower at times with a chance of showers and thunderstorms. Otherwise VFR. .Tuesday...Mainly VFR. && .MARINE... Cancelled the marine dense fog advisory for the eastern ocean waters as the fog bank shrinks and moves east. A tightening pres gradient between low pres to the north and high pres over the western Atlantic on Fri could bring marginal SCA conds to the near shore ocean waters and the Long Island south shore bays late day Friday, with gusts up to 25 kt, and then to the ocean waters Fri night aftn/eve. A strengthening sfc inversion will be developing over the waters, so despite increasing winds aloft mixing potential will be limited. A 15-20 kt sustained flow could however bring ocean seas up to 5 ft Fri night. No SCA at this time since the situation is either still marginal or too far out in time. Generally sub SCA conditions are expected Sat thru Tue in a weak flow regime, but could see a period of 20-kt gusts, from the SW Sat afternoon and then shifting E on Sunday. && .HYDROLOGY... Localized heavy rainfall is possible Sat night into Sunday morning as a cold front passes through. Quite a bit of spread in model guidance, with 1/4 to 3/4 inch of rain appearing likely, but potential for locally 1 to 2 inches of rain. Minor urban and poor drainage flooding appear to be the main issues. && .TIDES/COASTAL FLOODING... Water levels may reach minor flood thresholds along the south shore back bays of Nassau County and in western Long Island Sound with the Sunday afternoon/night high tide cycle. Forcing for increased water levels will be increasing E-NE flow as a front stalls to the south and strong high pressure sets up E of New England, along with increasing astronomical high tides with the full moon on Tue the 29th. && .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...None. && $$ SYNOPSIS...Goodman NEAR TERM...Goodman/PW SHORT TERM...Goodman LONG TERM...NV AVIATION...DS MARINE...Goodman/PW HYDROLOGY...Goodman/NV TIDES/COASTAL FLOODING... EQUIPMENT...

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