Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 220001 AFDOKX Area Forecast Discussion National Weather Service New York NY 801 PM EDT Fri Sep 21 2018 .SYNOPSIS... A cold front approaches and moves across overnight into early Saturday morning. The front eventually stalls south of Long Island Saturday into Saturday night. Meanwhile, high pressure will gradually build in from Southeast Canada and the Great Lakes. Strong high pressure builds to the north of the area on Sunday and then offshore early next week. A frontal system will then impact the area Tuesday into Wednesday, ending with a cold frontal passage Wednesday night. High pressure follows briefly for Thursday, before another frontal system impacts the area on Friday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Mainly cloudy conditions are expected, and dry weather initially will give way to increasing chances for showers and thunderstorms. Breezy S-SW flow will diminish as a cold front nears. Showers and thunderstorms with the cold front from a model consensus conveys they move in during the overnight and then decrease with southeast movement, making for very little rain towards the coast. The parent low with the cold front will be deepening but staying well within Southeast Canada without many sources of moisture available for the frontal system. There is some positive vorticity advection across the local area apparent in the mid levels within the forecast models. Forecast Showalter Indices indicate some elevated instability, but left thunderstorm mention as a slight chance in the forecast with most dynamics staying well northwest of the area. The front will be moving across during the overnight into early Saturday. Temps fall into the lower to mid 60s per models, statistical MOS blend. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... In the mid levels, heights will gradually lower Saturday into Saturday night across the area with a quasi-zonal flow. At the surface, high pressure will begin to build in from the Great Lakes Saturday. The local region will be on the eastern side relative to the center of the high pressure, with thereby northerly flow during the day to keep dry conditions. The models have a good consensus on conveying conditions staying dry through the day and the subsidence from the high pressure will allow for more sun. The flow will provide some downslope across coastal locations, making for adiabatic warming along the coastal areas. The GMOS was used for max temperatures Saturday, ranging mainly from the low to mid 70s, relatively warmer at the coast. The center of the high will remain north and west of NYC and build more north of the region Saturday night. For Saturday night, the winds will gain a more easterly component. Meanwhile though, the cold front that moved across the region will be slowing down and lingering in the Atlantic Waters to the east of the Delmarva. The GFS is indicating some return northward of this front along with some rain late Saturday night into very early Sunday morning with more easterly flow for the local area but other models are farther southward, maintaining dry conditions across the local area. Kept a dry forecast for the local area Saturday night. For min temperatures Saturday night, used a blend of MAV/ECS guidance which was relatively warmer than other guidance with more clouds mitigating radiational cooling. There is a moderate risk for the development of rip currents at the ocean beaches Saturday morning, with a low risk in the afternoon as winds diminish and seas subside. && .LONG TERM /SUNDAY THROUGH FRIDAY/... A confluent flow across eastern Canada and the northeast will allow for strong high pressure to pass to the north through Monday. There is some concern with a frontal wave associated with a shearing mid-level shortwave trough, but will maintain a dry forecast on Sunday with some morning clouds mainly near the coast. Any light rain should stay south of Long Island. The GFS which does produce some measurable rain across the NYC metro and Long Island appears to be overdone based on the depth of dry air and the northern placement of the upper jet in comparison to the model consensus. The weather then takes a downhill swing for the midweek as an upper trough out west races eastward with a frontal system impacting the area Tuesday into Wednesday. First of which will be with overrunning rain Monday night into Tuesday night and then with scattered convection on Wednesday. The cold front follows Wednesday night. Additional timing issues have now risen with the GFS trending against the model suite by stalling the front Wednesday night into Friday, with multiple waves of low pressure riding along the front. In this scenario, the kicker will be with a late week cold frontal passage. All the global models support the late week kicker, the differences though arise with the lead shortwave trough lifting out to the NE Wednesday night into Thursday. The magnitude of this feature and its wavelength separation with the next upper trough/surface frontal system, will determine whether the first boundary makes it through. Even the GGEM which sends the first front east of the area Wednesday night, is close enough for a coastal low to impact the area Thursday night into Friday. Thus, there remains quite a bit of uncertainly for the Thursday into Friday timeframe and have maintained a low chance for rain at this time. Seasonable temperatures will start the week, but it then gets warm and humid Wednesday in the warm sector. The end of the week is a bit tricky depending on the placement of the aforementioned frontal boundary. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... A cold front passes through late tonight, then high pressure returns on Saturday. Mostly VFR to MVFR. Chance of showers late. VFR follows behind the cold front early Saturday morning. S winds gusting up to 20 kt, becoming SW by midnight, then shifting NW behind the cold front late at night. N winds on Saturday gusting up to around 20 kt in the morning, with gusts subsiding in the afternoon. 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: Tempo MVFR cigs possible before 03z. Gusts might be only occasional. KLGA TAF Comments: Tempo MVFR cigs possible before 03z. Gusts might be only occasional. KEWR TAF Comments: Tempo MVFR cigs possible before 03z. KTEB TAF Comments: Tempo or VFR possible this evening., KHPN TAF Comments: Tempo VFR possible this evening. KISP TAF Comments: Brief periods of MVFR cigs possible into this. Gusts might be only occasional. .OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY... .Saturday night-Sunday...VFR. .Monday...VFR. .Tuesday and Wednesday...MVFR or lower in showers. SE Gusts 25 kt on Tuesday. && .MARINE... Increasing winds and seas will lead to SCA conditions tonight for all waters. Non-ocean waters will remain below SCA for seas but winds will gust to SCA levels. The ocean will observe increasing seas to 4 to 6 ft. The SCA conditions linger into Saturday just for the ocean as the seas will have some long period swell that keep seas elevated a little longer. SCA seas remain on the ocean until 18Z Saturday. Thereafter through the remainder of the weekend, local waters will drop to below SCA level conditions. Easterly winds strengthen Monday into Monday night and continue into Tuesday ahead of an approaching warm front. SCA conditions are likely to develop during this time with a small chance of gale force gusts on the ocean waters. High seas likely linger into Wednesday with a southerly flow as the warm front passes to the north and a cold front approaches late in the day. && .HYDROLOGY... No significant widespread rain expected through early Saturday. Total average rainfall expected to remain less than a quarter of an inch. Dry weather is then forecast for the rest of the weekend. A frontal system could bring locally heavy showers/tstms Tue into Wed, first via warm fropa on Tue, then again via trailing cold fropa on Wed. Anticipate only localized nuisance impacts at this early point. && .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...None. NY...None. NJ...None. MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ330-335- 338-340-345. Small Craft Advisory until 2 PM EDT Saturday for ANZ350-353- 355. && $$ SYNOPSIS...JM/DW NEAR TERM...JM/PW SHORT TERM...JM LONG TERM...DW AVIATION...JC MARINE...JM/DW/PW HYDROLOGY...JM/DW EQUIPMENT...

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