Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 262002 AFDOKX Area Forecast Discussion National Weather Service New York NY 402 PM EDT Sat May 26 2018 .SYNOPSIS...
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A back door cold front approaches from the north and east, and moves across the region tonight into early Sunday. The front becomes nearly stationary south of Long Island through Memorial Day as high pressure builds to the north. High pressure will build into the region through midweek, then low pressure may impact the region for the end of the week.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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Two rounds of precipitation are possible, one this evening with marginal to moderate surface instability this evening and convergence along sea breeze boundaries, as a weak upper short wave also moves into a flat ridge. Scattered thunderstorms will be possible, with the potential for heavy rainfall with any of the storms and as the storms possibly train across the same area. Cumulus clouds street have been seen on satellite with some buildup and showers along these lines. This is where some of the meso models, especially the HRRR are indicating potential for convection. Will have a break for several hours until the next round of precipitation moves in with the interaction of the back door cold front moving in from the north to northeast. And this front also will be enhanced with the weak shortwave moving through the northeast. Precipitation will be more likely with the front. And timing will be 03Z into NE CT, around 06Z into the lower Hudson Valley, and 09Z to 12Z through the remainder of the region. With the front instability is minimal to none with precipitation mainly statiform, especially behind the front. There is a moderate risk for rip currents today at area Atlantic Beaches.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
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The back door cold front will become stationary south of Long Island early Sunday morning, 12Z to 15Z, and additional shortwave energy will move through the northeast through Sunday night into early Monday. Again with little CAPE, and instability, precipitation will be mainly stratiform. There may still be some heavier more convective elements just behind the cold front Sunday morning with the potentially for heavier rainfall as these convective elements will be slow moving.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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A broad area of high pres will build over the region thru Wed. There will be a backdoor cfp on Tue. The timing is slightly faster than yesterday`s model suite, thereby suppressing the instability and chcs for shwrs to the s. The GFS is slower than the ECMWF and NAM, which is why pcpn is initiated closer to the cwa. The fcst remains dry. The dry wx then holds thru Wed, then increasing thetae could allow for some isold-sct shwrs and tstms on Thu. The modeling is not too aggressive attm wrt qpf, as the organized dpva is progged to remain w of the region closer to the main sys. Pops remain limited to slgt chc as a result. The main low, which is the remnants of Alberto, is progged to traverse the area Fri and Sat. This would present a better chc for organized rainfall, which could be locally hvy. The 12z data focuses the low on nrn New England, but this is likely to change over time, as is did from the prev 12z runs. Pw around 2 inches is suggested invof the low which seems reasonable based on the subtropical origins. The nbm was used for all but Tue high temps where the warmer Superblend was used.
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&& .AVIATION /20Z SATURDAY THROUGH THURSDAY/... A cold front will approach from the north into this evening and move across late tonight, but will remain not far to the south thereafter through Sunday. VFR through much of tonight with only MVFR/IFR coming in very brief periods associated with any showers or thunderstorms. These are forecast for city terminals and KHPN in the timeframe of 19-22Z with this activity being more in the vicinity for other terminals. Window for showers and thunderstorms may occur an hour later than forecast. Mainly dry conditions expected tonight until the overnight period, after 07Z, when rain returns with and behind the frontal passage. Rain lasts through the rest of the TAF period with lowering conditions for Sunday into MVFR/IFR. Regarding winds, SW flow near 10 kt this afternoon with some gusts up to 20 kt will decrease and become more variable in direction tonight. The flow becomes more E-NE Sunday around 10 kt with gusts developing in the 15-20 kt range. .OUTLOOK FOR 18Z SUNDAY THROUGH THURSDAY... .Sunday afternoon...Rain likely. Mainly IFR. ENE winds G20kt. .Sunday night...IFR cigs continue with lingering rain. .Monday...MVFR cigs in the morning along with slight chance of light rain, then VFR. .Tuesday-Wednesday...VFR. .Thursday...Mainly VFR. && .MARINE...
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With a weak pressure gradient across the waters today and tonight, winds and seas have remained below SCA levels, and are expected to remain below through tonight. An increasing NE to E flow behind a back door cold front, with high pressure building to the north will result in both winds and seas increasing to SCA levels Sunday morning and continuing into Sunday night, mainly on the ocean waters, Gusts across eastern Long Island Sound, and the bays of Long Island may be near SCA levels Sunday. However expect gusts to be more occasional, and will not issue a SCA for those forecast waters at this time. Across the ocean waters have cancelled the SCA that were in effect today and tonight, and posted a new SCA for the ocean waters Sunday and Sunday night. Winds are expected to remain blw sca lvls Mon-Thu. 5 ft seas are possible Mon on the ocean, otherwise they will stay blw sca lvls thru Thu.
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&& .HYDROLOGY...
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Rainfall amounts this weekend could vary quite a bit across the area, with mainly two rounds of rainfall, one into this evening, then later tonight through Sunday night. Total rainfall will be also vary with around a third of and inch inland to 3/4 inches along the coast. Locally heavy rainfall will be possible, especially through early this evening in any thunderstorms that develop, and then again late tonight into Sunday. Cannot rule out minor urban and poor drainage flooding, mainly tonight into Sunday morning. No significant hydrologic impacts are anticipated Sun night through Thu. There is a low potential for locally heavy rain Fri- Sat.
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&& .TIDES/COASTAL FLOODING... Water levels may be near minor flood thresholds along the south shore back bays of Nassau County and in western Long Island Sound with the Sunday late afternoon and evening 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...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 6 AM Sunday to 6 AM EDT Monday for ANZ350-353-355.
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&& $$ SYNOPSIS...12/19 NEAR TERM...19 SHORT TERM...19 LONG TERM...12 AVIATION...JM MARINE...12/19 HYDROLOGY...12/19 TIDES/COASTAL FLOODING... EQUIPMENT...

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