Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 252043 AFDOKX Area Forecast Discussion National Weather Service New York NY 443 PM EDT Tue Apr 25 2017 .SYNOPSIS...
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Weakening low pressure will move slowly up the Mid Atlantic coast through Wednesday, pass southeast of Long Island Wednesday evening, and then dissipate east of New England later Wednesday night. A weakening cold front will approach from the northwest Thursday and Thursday night, then also dissipate over the area on Friday. Another cold front will approach from the north Friday night and Saturday, then presses to the south Saturday night. The front will then gradually lift north as a warm front, pushing to the north of the area Monday. A cold front will then move across Monday night, followed by weak high pressure building in on Tuesday.
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&& .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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Rain bands ahead of the surface low, currently over eastern NC, continue to pivot up into the area on nose of 40-50 kt SE H8 jet. Mid level instability is aiding efficient warm rain processes, with embedded locally heavier rain noted on Long Island earlier today and now moving up the Jersey shore toward NE NJ and skirting NYC into this evening. High-res guidance also shows additional similar rain bands developing to the south later this evening and spreading in overnight. Offshore lightning strikes to the south occurring in bands of deeper elevated instability marked by RAP Showalter indices -2C or lower, and these bands of instability should reach NYC metro and Long Island late this evening, then spread northward to much of the interior during the first half of the overnight, so mentioned chance of thunder. Precip starts to taper off late as LLJ shifts to the NE. Meanwhile E-NE winds will continue to increase, with peak wind gusts 35-40 mph by about 8-10 PM, then diminishing overnight and backing NE. Low temps tonight will be in the lower 50s.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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On Wednesday, the stacked low will be slowly moving south and east of Long Island. Expect scattered showers to continue, mainly in the morning and especially over Long Island and southern CT, then tapering off in the afternoon. The close proximity of the stacked low should keep low clouds around through the day and possibly some patchy fog, with highs mainly in the lower 60s. As the upper low passes just to the SE Wed night, could see some redevelopment of showers mainly across Long Island mainly after midnight. Lows will again be in the 50s.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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Northern stream ridging builds over the area on Thursday keeping things dry. However, underneath the associated subsidence inversion, the lowest 100-150 hPa will be fairly saturated, so have increased cloud cover and decreased temperatures on Thursday. For now generally going 60-70 across the region, though there is some potential these could be 5 to maybe even 10 degrees to warm. A northern stream shortwave passes to the north Thursday night warranting chance pops over NW 1/3 of the CWA and slight chance pops elsewhere. With showalters progged to fall to 0 to2, have added thunder to the forecast as well. Lows Thursday night should be around 10 degrees above normal. A northern northern stream shortwave passes by, a little closer this time, on Friday, warranting chance pops everywhere. Showalter indices warrant a chance of Thunder. Note, the GFS is faster than most other solutions with the associated cold front, so used a non-GFS blend for timing the cold front and precipitation. As a result, could see locations away from the coast have highs from the mid 70s to around 80. As a result, areas mainly west of the Hudson could see CAPES in the afternoon of around 1000 J/kg along with 40-50 kt of shear so some strong to severe storms are possible there Friday afternoon. The region is under quasi zonal flow Friday night-Saturday as ridging builds to our south and a northern stream trough passes to the north. Friday night should be dry, but could see some isolated- scattered showers and possibly a thunderstorm by Saturday afternoon/evening ahead of a backdoor cold front. Favored the faster ECMWF timing of the front (based on historical superior ECMWF handling of backdoor fronts vs. the GFS). Deep layered ridging builds over the area Saturday night-Sunday night, then the axis slides to the east on Monday. At the surface, the back door front pushes well to the South by Sunday morning, then slowly lifts to the north as a warm front, lifting to the north on Monday. The surface warm front motion warrants a slight chance of rain Sunday and a chance of rain Sunday night. There is then a chance of showers Monday morning and a chance of showers and thunderstorms Monday, once solidly in the warm sector. A vigorous northern stream trough approaches Monday night, then lifts to the north on Tuesday, with its associated surface cold front pushing through Monday night. As a result, have a chance of thunderstorms Monday night, then a slight chance of showers Tuesday. Temperatures Friday-Tuesday were based on the Superblend, with NAM 2- meter temperatures and a mix down from 975-925 hPa per BUFKIT soundings added in on Friday. Temperatures should remain well above normal during this time frame, with Saturday the warmest day - with highs around 80 in the NYC Metro.
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&& .AVIATION /20Z TUESDAY THROUGH SUNDAY/... Low pressure slowly moves up along the Mid-Atlantic coastline today and tonight. Generally expect IFR conditions, with LIFR possible at times through tonight. Intermittent rain will be locally moderate to heavy at times today into tonight. East/northeast winds prevail, with speeds in the 15 to 20 kt range. Gusts will range 25 to 30 kt this afternoon with some decrease tonight. Gusts should become less frequent overnight. LLWS is possible this evening with SE winds 45-50 kt at 2kft, mainly east of NYC terminals. 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: Uncertain of exactly when next round of heavy rain will be. Possible amendment to insert 2 hour TEMPO group for 1SM in heavy rain for sometime this afternoon. KLGA TAF Comments: Uncertain of exactly when next round of heavy rain will be. Possible amendment to insert 2 hour TEMPO group for 1SM in heavy rain for sometime this afternoon. KEWR TAF Comments: Uncertain of exactly when next round of heavy rain will be. Possible amendment to insert 2 hour TEMPO group for 1SM in heavy rain for sometime this afternoon. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Uncertain of exactly when next round of heavy rain will be. Possible amendment to insert 2 hour TEMPO group for 1SM in heavy rain for sometime this afternoon. KHPN TAF Comments: Uncertain of exactly when next round of heavy rain will be. Possible amendment to insert 2 hour TEMPO group for 1SM in heavy rain for sometime this afternoon. KISP TAF Comments: Visibility could vary between MVFR and IFR 18Z-22Z. .OUTLOOK FOR 12Z WEDNESDAY THROUGH SATURDAY... .Wednesday-Wednesday Night...IFR in possible rain and fog. Potential for IFR/LIFR in fog Wednesday night. .Thursday...MVFR/IFR to start...with gradual improvement to VFR. .Friday...Chance of MVFR in showers/thunderstorms. .Saturday...VFR. && .MARINE...
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SCA conditions occurring on all waters as expected. Winds on the western ocean waters, western Long Island Sound, and possibly NY Harbor could briefly peak at 35 kt this evening before diminishing. Winds should diminish overnight, with advy conditions abating on the Harbor/Sound/Bays by 06Z. Lingering ocean swells above 5 ft and also 1 ft above WaveWatch and NWPS are likely to continue into at least Wed night. A relatively relaxed pressure gradient Thursday-Sunday will keep winds over the waters around Long Island to 15 kt or less. However, gradually diminishing swells will keep seas over all or parts of the coastal ocean waters at or above 5 ft through Friday night. All waters should experience sub-advy conditions Saturday and Sunday.
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&& .HYDROLOGY...
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Total rainfall of 0.75 to 1.5 inches is expected through Wednesday. The highest amounts are most likely to occur across Northeast New Jersey, also across southern CT. Hourly rainfall rates close to 1/2 inch per hour with the heaviest rain could cause brief/localized poor drainage flooding. No significant (0.5 inches or more) widespread rainfall is forecast from Thursday through at least Monday. However, isolated strong convection could produce locally heavy rainfall Friday and again on Monday. In areas where this occurs, there is the potential for the ponding of water on roadways and a very low chance of minor flooding of known poor drainage areas.
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&& .TIDES/COASTAL FLOODING...
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In response to a low pressure system moving northward along the eastern seaboard, minor coastal flooding is expected across the lower NY/NJ Harbor, the South Shore Bays of western Long Island including Queens and Brooklyn, and locations along the western Long Island Sound for the high tide this evening. Additionally, localized moderate coastal flooding is possible along the south shore back bays of Nassau County this evening. Only 1/2 to 1 foot of surge is needed to reach minor flood thresholds this evening, and strong easterly winds should pile water across these areas. A Coastal Flood Advisory remains in effect. Thereafter, minor coastal flooding thresholds will be approached in the same areas once again with the lower Wed morning high tide, and possibly briefly exceeded along the southern bays of Western Long Island. Right now at most it would appear that a statement could be needed for southern Nassau southern Queens. Will wait after this evening`s high tide cycle to see trends/anomalies and issue any products as needed. More widespread minor coastal flooding is possible with Wednesday night`s high tide cycle. Best chances for minor inundation will be at the south shore back bays of Nassau and Queens, but at least a statement could be needed for other areas as minor thresholds have a chance to just be reached in a few spots. Only 1/3 to 3/4 of a foot of surge is needed to reach minor flood thresholds Wed night. In addition, the elevated water levels combined with a prolonged period of 5-9 ft breaking surf tonight into Thu will result in beach erosion issues and may cause some localized dune toe erosion during the high tides tonight into Wed night.
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&& .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...Coastal Flood Advisory from 10 PM this evening to 1 AM EDT Wednesday for CTZ009-010. NY...Coastal Flood Advisory until 10 PM EDT this evening for NYZ074- 075-178. Coastal Flood Advisory from 10 PM this evening to 1 AM EDT Wednesday for NYZ071-073-078-177. Coastal Flood Advisory until 11 PM EDT this evening for NYZ080- 179. NJ...Coastal Flood Advisory until 10 PM EDT this evening for NJZ006- 106-108. MARINE...Small Craft Advisory until 2 AM EDT Wednesday for ANZ330-335- 338-340-345. Small Craft Advisory until 6 AM EDT Thursday for ANZ350-353- 355.
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&& $$ SYNOPSIS...Goodman/Maloit NEAR TERM...Goodman SHORT TERM...Goodman LONG TERM...Maloit AVIATION...JM MARINE...Goodman/Maloit HYDROLOGY...Goodman/Maloit TIDES/COASTAL FLOODING...

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