Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 181810 AFDOKX Area Forecast Discussion National Weather Service New York NY 210 PM EDT Tue Sep 18 2018 .SYNOPSIS... A cold front will move across the region by early this evening. High pressure then ridges down southeastern Canada through Thursday, then retreats to the northeast Thursday night. A cold front approaches from the west on Friday, then crosses the area Friday night, followed by high pressure building in for the weekend into early next week. && .NEAR TERM /THROUGH TONIGHT/... Flash flood watch remains in effect until 7PM for Northeast NJ, the Lower Hudson Valley, NYC, Western Long Island and Southwest CT. Main story is the heavy showers with scattered embedded thunderstorms moving across the region. This is confined to the coastal sections across NYC, Southern CT and Long Island with northern extent primarily up to Bergen County NJ and Southern Westchester NY. The activity will soon be moving across Southeast Suffolk County. Rainfall rates up to around one inch per hour at times can be expected with some areas having 1 to 1.5 inches per hour rainfall rates. For most of the Lower Hudson Valley and more interior portions of the region such as Western Passaic NJ and Northern Fairfield CT, flash flood chances are decreasing as just some light rain showers remain. In terms of weather features, a cold front is making progress moving through the region. The low attached to this front with the remnants of Florence will be moving into the Gulf of Maine. The front and low move farther away from the region tonight into the Atlantic. In terms of forcing and moisture, areas seeing the heavy rain still have a high precipitable water environment of about 2.25 inches. The profile of winds is SW from low to mid levels and this unidirectional shear is helping create for training of cells where a series of showers and thunderstorms moves across the local region. The one feature that has been limited is instability, with models showing up to near 1500 J/kg of surface CAPE. For tonight, with the low and front moving farther away, drier conditions will move into place as surface winds become more northerly. High pressure will begin to build in tonight from the Great Lakes. There remains a high rip current risk today. && .SHORT TERM /WEDNESDAY/... High pres builds across Quebec with a drier airmass building in. Pwats fall to an inch or less. There is hint of a weak backdoor frontal passage, which could spark an isold shower. The fcst was left dry for now as the convergent region of the jet arrives. However, if the modeling becomes more consistent a few shwrs or sprinkles may need to be added. The NBM was used for temps. There is a moderate rip current risk for Wed. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... The core of a deep layered ridge builds to our southwest then south Wednesday night through Thursday night, with its axis sliding offshore on Friday. Subsidence under the ridge should keep things dry Wednesday night- Thursday night and relatively cloud free Wednesday night and Thursday. Week low level warm advection should bring some cloud cover on Thursday night. Lows Wednesday night should be a few degrees above normal. Highs on Thursday should be a few degrees below normal and lows Thursday night around 5 degrees above normal. A 700 hPa shortwave working its way up the back side of the ridge on Friday warrants slight chance pops for showers/thunderstorms to the northern Tier of the Lower Hudson Valley/W Passaic County/far N Fairfield County, with dry conditions expected elsewhere. Highs on Friday should be around 5 degrees above normal. A northern stream trough passes to the north Friday night, with mainly zonal flow over the region, the bulk of the energy associated with this trough will stay north of the area. As a result only have slight chance pops Friday night. The region remains under zonal-wsw flow aloft Saturday-Monday. The ECMWF is along in suggesting shortwaves embedded in the flow could bring some showers on Sunday and possibly Sunday night. So have slight chance pops Sunday/Sunday night and have gone the remainder of the time frame from Saturday-Monday. Temperatures should be above normal Friday night, then near normal Saturday, with below normal temperatures forecast Sunday and Monday. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... A cold front passes late this afternoon as high pressure builds well to the north tonight into Wednesday. Any lingering MVFR/IFR conditions in showers/thunderstorms improves late this afternoon and evening. Generally VFR is anticipated tonight into Wednesday morning, although cannot rule out some patchy stratus and fog overnight. Winds shift to the N/NW, and diminish late this afternoon and overnight. Northerly winds pick up Wednesday morning to 10-15 kt. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component fcsts, can be found at: http:/www.weather.gov/zny/n90 KJFK TAF Comments: Timing of improvements to ceilings/visibilities could be off an hour or two late this afternoon, so amendments are possible. KLGA TAF Comments: Timing of improvements to ceilings/visibilities could be off an hour or two late this afternoon, so amendments are possible. KEWR TAF Comments: Timing of improvements to ceilings/visibilities could be off an hour or two late this afternoon, so amendments are possible. KTEB TAF Comments: Timing of improvements to ceilings/visibilities could be off an hour or two late this afternoon, so amendments are possible. KHPN TAF Comments: Timing of improvements to ceilings/visibilities could be off an hour or two late this afternoon, so amendments are possible. KISP TAF Comments: Timing of improvements to ceilings/visibilities could be off an hour or two late this afternoon, so amendments are possible. .OUTLOOK FOR 18Z WEDNESDAY THROUGH SUNDAY... .Wednesday afternoon...VFR. N winds G15-20KT possible. .Wednesday night-Thursday...VFR. .Thursday night...Chance of showers with MVFR possible. .Friday-Friday night...VFR during the day, then a chance of showers with MVFR at night. .Saturday-Sunday...An early shower Saturday, then VFR through the weekend. && .MARINE... Winds and seas build to Small Craft Advisory (SCA) levels on the coastal ocean waters today, and just below on the remaining waters. A few 25 kt gusts cannot be ruled out especially on the S Shore Bays. The SCA on the coastal ocean waters remains through tonight as seas stay in the 3-5 ft range, and may need to be extended through Wednesday as the NE flow builds seas once again. Winds below SCA levels elsewhere. The waters around Long Island should experience a light to moderate pressure gradient from Wednesday night-Saturday night, with winds around 15 kt or less. Gusts to around 20 kt are possible on the coastal ocean waters Wednesday night. Seas on the coastal ocean waters could be around 5 ft, especially over the southern 1/2 of each zone Wednesday night and Thursday. Otherwise, sub-Small Craft Advisory conditions are expected from Wednesday night through Saturday night. && .HYDROLOGY... Up to another 1 inch of rainfall can be expected with the shower and thunderstorm activity through this afternoon. Some locally lower and higher amounts are possible. Rainfall rates of one inch per hour or greater can be expected at times, especially this afternoon as the main frontal system comes through. Some minor flooding can be expected, with a chance for flash flooding, mainly along the coast for the rest of the afternoon. No significant hydrologic impacts are expected from later tonight through Monday. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Flash Flood Watch until 7 PM EDT this evening for CTZ005-006- 009-010. NY...Flash Flood Watch until 7 PM EDT this evening for NYZ067>075- 176>179. High Rip Current Risk until 8 PM EDT this evening for NYZ075- 080-081-178-179. NJ...Flash Flood Watch until 7 PM EDT this evening for NJZ002-004- 006-103>108. MARINE...Small Craft Advisory until 6 AM EDT Wednesday for ANZ350-353- 355. && $$ SYNOPSIS...JMC/Maloit NEAR TERM...JMC/Maloit/JM SHORT TERM...JMC LONG TERM...Maloit AVIATION...PW MARINE...JMC/Maloit/JM HYDROLOGY...JMC/Maloit EQUIPMENT...

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