Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 280822 AFDOKX Area Forecast Discussion National Weather Service New York NY 422 AM EDT Wed Sep 28 2016 .SYNOPSIS...
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Strong high pressure builds in from the north today forcing an old frontal boundary further south and east. Meanwhile...low pressure will meander about the Ohio Valley and Mid Atlantic regions into the weekend resulting in an extended period of unsettled weather. The low will weaken and move slowly northeast early next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Low clouds and fog have developed across eastern Long Island and southern CT early this morning...as well as patchy fog further west where radiational cooling has been occurring. The fog should burn off this morning...although the low clouds are expected to expand wwd as the day progresses with an increasing easterly low level flow trapping moisture beneath an inversion. Strong high pressure over the Canadian Maritimes will start to build southward today with a CAD signature becoming established in New England. Meanwhile...a closed low pressure system moves into the Ohio Valley. All guidance except for the NAM is indicating light rain or DZ developing across the area this afternoon as a result of increasing WAA aloft...although this will depend on the degree of dry air that moves in from the high to the north. East winds increase later this morning with sustained speeds between 10 and 20 mph with gusts of 15 to 25 mph...highest at the coast. Temperatures will be near normal. There is a moderate risk of rip current development at Atlantic ocean beaches today.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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The main weather story will be the influence of the large cutoff low pressure system meandering around the Ohio Valley has on the local area. The strong high will remain to the north through Thursday which now looks to keep pcpn mainly confined to western portions of the forecast area. Thus...have maintained likely pops only for this area with lower PoPs elsewhere. Again the degree of dry air that works in from the north will determine when and where it will rain. Think that places west of the Hudson River have the highest chance for a few tenths of an inch through this time. Light rain or drizzle possible to the east with a moderate east flow continuing. Winds strengthen slightly on Thu with gusts up to 30 mph at the coast. Little diurnal range in temps Wed Night/Thu with abundant cloud cover and a maritime airmass.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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NWP guidance remains in good agreement on the big picture through the weekend with a large upper low completely cutting off from the westerlies and stalling over the Ohio Valley through Saturday, then lifting across the Great Lakes on Sunday and weakening into an upper trough that slides across the Northeast on Monday. Meanwhile, as a strong upper high builds over the Western Atlantic, upper level confluence to its north where it meets the westerlies will maintain strong surface high pressure over northern New England and the Canadian Maritimes,that should nose down into our area and keep a warm front to our south. This combination will keep us in an unsettled weather pattern through at least the weekend with periods of rain, possibly heavy at times. The heavier rain could occur late Thursday night into Friday morning via strengthening easterly low level Atlantic inflow, moistening mid levels via deep southerly flow aloft, a mid level vort max riding up the coast, and increasingly difluent flow aloft. Another period of heavy rain may come to Long Island and southern CT on Saturday as another mid level impulse rides up the coast and as a weak wave of low pressure forms along the front just to the south. In between these bouts of relatively heavier rain, skies should remain overcast, with periods of intermittent light rain. A triple point low could pass through Saturday night into Sunday morning. Associated lift and elevated instability could result in a rumble or two of thunder during this period. And with the triple point low, winds diminish somewhat for a period with plenty of moisture still around, resulting in a decent chance of some fog. As the upper low lifts into the Great Lakes on Sunday, the triple- point low and/or occluded front should slowly lift across, with precip becoming more showery in nature. The upper low will continue to weaken and move east, but still close enough to mention at least a slight chance of a shower on Monday. High pressure then likely keeps Tuesday dry.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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Fog has developed across KGON, reducing vsbys and cigs to IFR or less. This will need to be monitored to see if this spreads to any of the other terminals. Otherwise, other than some mid level clouds impacting the eastern terminals, expect mainly VFR conditions overnight. The forecast then transitions over to a prolonged period of sub-VFR conditions starting this morning and likely persists into the first half of the weekend. High pressure builds south from eastern Canada and noses into the area today. Meanwhile, low pressure will drop south across the Great Lakes and into the Ohio Valley states. This will result in a strengthening NE flow with overrunning clouds and possible light rain or drizzle. Widespread MVFR conditions are forecast to develop from east to west. Thinking that conditions could start to fall between 09Z and 13Z, from east to west. here is the possibility for these ceilings to move in earlier than forecast, as well as drop into the IFR category, especially for the coastal terminals. Light rain is a possibility, but not expecting restrictions to visibility at this time. Another potential wrinkle in the forecast is the magnitude of the high building in from the north. Should the high build a bit farther south, this could improve conditions for a time. Light and variable winds becoming NE around 10 kt around daybreak. By mid to late morning, NE winds increase to 10-15 kt and become gusty at times, as high as 20-25 kt at the coast. ...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: Medium/high confidence on winds, lower confidence on ceilings. Amendments may be needed for changing flight categories. KLGA TAF Comments: Medium/high confidence on winds, lower confidence on ceilings. Amendments may be needed for changing flight categories. KEWR TAF Comments: Medium/high confidence on winds, lower confidence on ceilings. Amendments may be needed for changing flight categories. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Medium/high confidence on winds, lower confidence on ceilings. Amendments may be needed for changing flight categories. KHPN TAF Comments: Medium/high confidence on winds, lower confidence on ceilings. Amendments may be needed for changing flight categories. KISP TAF Comments: Chance of fog development this morning which could reduce visibilities. Medium/high confidence on winds, lower confidence on ceilings. Amendments may be needed for changing flight categories. .Outlook for 06Z Thursday through Sunday... .WED NIGHT...Widespread MVFR ceilings, possibly IFR. NE winds G20-25KT at the coastal terminals. .THU-SAT...IFR/MVFR in showers. NE winds 15-20 kt with gusts 25-30 kt possible THU-FRI. .SUN...Mainly VFR but MVFR possible with a chance of showers. N winds 10-20 kt.
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&& .MARINE...
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Have maintained SCA east of Moriches inlet due to marginal seas early this morning. East winds will increase later this morning as well with SCA conds developing on all waters. Timing could be a few hours too early...especially on the non-ocean waters but wanted to give a few hours of padding. Then as the pressure gradient tightens further, easterly gales appear likely from Thu into Fri morning mainly on the ocean, but perhaps also on the nearby bays of eastern Long Island and eastern Long Island Sound, with SCA conds on the harbor and western Sound. Issued gale watch for the ocean for Thu into Thu night. SCA conds are likely to continue thereafter on all waters into Fri evening, on the eastern Sound/bays into late Fri night, and on the ocean into Sat.
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&& .HYDROLOGY...
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Any rain through tonight should light and mainly confined to areas north and west of NYC, with rainfall totals less than 1/3 inch. Total basin average rainfall from Thu through Sat should range from 1 to 2 inches, highest east, with potential for local amounts of 2-3 inches across parts of Long Island and southern CT. The rain could potentially be heavy at times late Thursday night into Friday morning as well as at some point during Saturday. With this being a long-duration event, major hydrologic impacts are not expected but at least minor flooding could be possible.
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&& .TIDES/COASTAL FLOODING... A persistent moderate easterly flow during mid to late week may combine with increasing astronomical high tides associated with the new moon on Friday to cause minor to locally moderate coastal flooding. The high tide cycles from Thu night into Fri morning appear to be of most concern. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory from 8 AM this morning to 6 PM EDT Thursday for ANZ330-335-338-340-345. Gale Watch from Thursday morning through late Thursday night for ANZ350-353-355. Small Craft Advisory from 8 AM this morning to 6 AM EDT Thursday for ANZ353-355. Small Craft Advisory until 6 AM EDT Thursday for ANZ350.
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&& $$

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