Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 181430 AFDOKX Area Forecast Discussion National Weather Service New York NY 1030 AM EDT Tue Sep 18 2018 .SYNOPSIS... The remnants of Florence will pass through the region this morning, followed by a cold front this afternoon. 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/...
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Main change this morning was increasing chances for flash flooding this afternoon. Flash flood watch for the Lower Hudson Valley, Northeast NJ, Western Long Island, and Southwest CT including NYC from 11AM until 7PM. This is a combination of where heavy rain occurred during the previous day and where heavy showers and thunderstorms are expected this afternoon. This includes the highly urbanized portions of the region and these areas are where many mesoscale models are showing a heavy line of showers and thunderstorms moving across this afternoon. While these heavy showers and thunderstorms are still expected even for easternmost portions of the region (namely Southeast CT and Suffolk County NY), these portions of the region have higher flash flood guidance so flooding would be more minor nuisance flooding. The remnants of Florence lift to the northeast this morning followed by a 850-500 hPa trough passing this afternoon. Instability is increasing per LAPS, and will continue to do so until the surface trough/cold front passes this afternoon. The position of the main low, tracking roughly along the Mass Pike, will keep the best directional shear north of the area. As a result, severe thunderstorms are not expected, although the mesoscale environment will continue to be monitored through the day. Pops were updated to reflect faster end time of High resolution models and the 6Z runs of NAM and GFS. Expect precipitation to be done across most of the Tri-state by 6pm, with the entire area in the clear by 8pm. Southerly flow this morning with the low level jet should produce the strongest gust potential through 15-17z. The surface trough coming through then lightens wind as it progresses across the CWA. Light wind fields behind the front with winds up to 850 hPa maxing out at 20 kt. A blend of the mos was used for temperatures today and tonight. There is a high rip current risk today.
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&& .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 MONDAY/... 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 /14Z TUESDAY THROUGH SATURDAY/...
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The remnants of Florence will interact with a cold front approaching from the NW today. The front will move across the region this afternoon and evening. MVFR to locally IFR conds prevailing across the terminals and should generally persist until the cold front passes this afternoon/evening. Showers continue to increase in coverage as the front nears with a line of tstms expected in the 16z-23z timeframe, NW to SE. VFR returns thereafter, except there could be patchy MVFR/IFR fog development outside of NYC tonight. S-SW winds 10-15 kt with a few gusts 20 kt coastal terminals, 5-10 kt elsewhere. Winds then diminish this afternoon. Winds shift to the NW-N after the frontal passage this aftn/eve. 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: Wind direction could be off by 30 degrees 16-00z, depending on cold frontal progression. Improving conditions may be off a few hours as well. The afternoon KJFK haze potential forecast is YELLOW, which implies slant range visibility 4-6SM outside of cloud. KLGA TAF Comments: Wind direction could be off by 30 degrees 16-00z, depending on cold frontal progression. Improving conditions may be off a few hours as well. The afternoon KLGA haze potential forecast is YELLOW, which implies slant range visibility 4-6SM outside of cloud. KEWR TAF Comments: Wind direction could be off by 30 degrees 16-00z, depending on cold frontal progression. Improving conditions may be off a few hours as well. The afternoon KEWR haze potential forecast is YELLOW, which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Wind direction could be off by 30 degrees 16-00z, depending on cold frontal progression. Improving conds may be off a few hours as well. KHPN TAF Comments: Wind direction could be off by 30 degrees 16-00z, depending on cold frontal progression. Improving conditions may be off a few hours as well. KISP TAF Comments: Wind direction could be off by 30 degrees 18-02z, depending on cold frontal progression. Improving conditions may be off a few hours as well. .OUTLOOK FOR 12Z WEDNESDAY THROUGH SATURDAY... .Wednesday ...VFR. N winds G15-20KT possible. .Thursday...VFR. .Friday...Chance of showers with MVFR conditions at times. .Saturday...Mainly VFR.
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&& .MARINE... Minor changes were made with this update to reflect the latest trends in observations and guidance. Main change was to accelerate the end time of any precipitation. 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 was extended 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...
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Up to 1-2 inches 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, highest chances across western sections of the region where flash flood watch is in effect and lower chances to the east. No significant hydrologic impacts are expected from later tonight through Monday.
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&& .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...
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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.
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&& $$ SYNOPSIS...JMC/Maloit NEAR TERM...JMC/Maloit/JM SHORT TERM...JMC LONG TERM...Maloit AVIATION...PW MARINE...JMC/Maloit/JM HYDROLOGY...JMC/Maloit/JM EQUIPMENT...

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