Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 181750 AFDOKX Area Forecast Discussion National Weather Service New York NY 150 PM EDT Fri May 18 2018 .SYNOPSIS... A stationary front will remain south of the area today, then return northward through the region as a warm front on Saturday. A cold front will pass Sunday into Sunday Night. High pressure will briefly build into the region Monday, before unsettled weather returns for midweek. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Based on latest satellite imagery and guidance, have diminished cloud cover somewhat this afternoon across northern portions of the Lower Hudson Valley and interior southern CT. This may result in skies becoming partly sunny at times across these locations. Remainder of forecast remains on track with highs in the 60s. High pressure centered over Quebec will continue to strengthen today, feeding dry air into the area. The influence of the high will keep rain suppressed to the south this afternoon. Easterly winds will be brisk, especially LI, with the high to the north and front to the south.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Rain chances increase tngt with the warm front approaching the area. Timeheights show the mid lvls saturate by around 3z invof the city. Progress is slow newd thereafter. Periods of rain fcst for Sat with the warm front passing thru the cwa. Despite the increasing thetae, elevated CAPE is minuscule in both the NAM and ECMWF, and nil in the GFS. As a result, tstms will not be included in the fcst attm. For temps, the Superblend was used tngt, with the blend of all the models used on Sat to give more weight to the raw 2m data. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... Models coming into good agreement with a weak trough over the Ohio Valley shearing NE, ahead of a couple of northern stream shortwaves digging towards the Ontario/Quebec border Saturday Night. The axis of southern and northern stream energy slides through the NE Sunday, with mean trough lingering into Monday. At the surface, good agreement with broad southern low pressure lifting northeast through the Ohio Valley into the Great Lakes on Saturday, and up the St Lawrence River Valley Saturday night. Its associated warm front should be able to move north through much of the region Saturday night as a 35-40 kt LLJ moves across coastal areas, and cold front slowly approaches from the west. Overall mid- upper level forcing is modest at best, with main trigger being convectively induced vorticity axis/maxima rotating through the region around the periphery of Bermuda ridging. With marginal instability in sub-tropical airmass advecting up the coast, potential exists for a few thunderstorms with heavy downpours late Sat Eve along warm front as it moves north. Best chance may be across eastern portions of region, coincident with better LLJ forcing. Models in good agreement with weak shortwave axis (remnants of southern trough) crossing the region on Sunday, as stronger northern stream shortwave passes through Quebec. At the surface, confidence is increasing in a weak cold front passing through the region Sunday aft/eve. Sct shower/tstms are possible along the front Sun. Heavy downpours would be main threat with any thunderstorms in sub- tropical airmass, but with marginal but unidirectional deep layer shear, cant rule out a couple of stronger storms or line segments developing/moving across the interior/nyc/nj metro. Model agreement is increasing on potential for a period of drying Sunday night into Monday as Canadian high pressure builds down into the NE, and cold front sags well south towards the Mid Atlantic. NE troughing appears to briefly give way to zonal upper flow heading into Tuesday, before good agreement on northern stream amplifying into the NE US for mid to late week. In terms of sensible weather, high pressure could maintain control Monday NIght into Tuesday as it slides through, but will be dependent on any upstream disturbances riding through the flow. Thereafter, potential for unsettled weather increases in mid week due to northern stream amplification, with potential for high pressure to return late week. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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High pressure will begin to shift offshore tonight, followed by a warm front moving through tomorrow morning into the early afternoon. Sustained NE-E winds generally 10-15 kt with occasional gusts up to 25 kt will prevail into the evening. Speeds may briefly decrease overnight, then occasionally gust again by morning as the warm front moves to the north. Have delayed the onset of MVFR conditions and expected rainfall. Conditions will likely stay VFR through the evening, with cigs perhaps lowering near the VFR/MVFR cusp in the evening. MVFR will be more likely after midnight, particularly after rain begins followed by IFR towards morning with the warm front. Rain may be more occasional/light by tomorrow 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: Occasional gusts to 25 kt possible. KLGA TAF Comments: Occasional gusts to 25 kt possible. KEWR TAF Comments: Gusts may become occasional this evening. KTEB TAF Comments: Gusts may become occasional this evening. KHPN TAF Comments: Occasional gusts to 20 kt possible. KISP TAF Comments: Gusts may become occasional this evening. .OUTLOOK FOR 18Z SATURDAY THROUGH WEDNESDAY... .Saturday...IFR or lower in occasional showers or drizzle. .Saturday night...Showers, isolated thunderstorms. MVFR to IFR conditions possible. .Sunday-early Sunday evening...A chance of showers. A chance of thunderstorms in the afternoon. MVFR conditions possible. .Rest of Sunday night-Tuesday...Mainly VFR, MVFR or lower possible at times in showers Monday night and Tuesday. .Wednesday...MVFR or lower possible in showers with cold frontal passage.
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&& .MARINE... Sca winds and seas develop today and tngt. The sca cond continue on the ocean Sat, with mrgnl sca winds on the protected waters. Marginal SCA gusts are then possible on the ocean for a period Sat night into Sunday due to a strengthening LLJ. Ocean seas should remain elevated through Sunday night, possibly into Mon morning E of Moriches Inlet. A weak gradient is expected Monday into Tuesday as high pressure moves across the area, with tranquil winds and subsiding s swell. && .HYDROLOGY... No hydrologic impacts are anticipated thru Sat. Localized heavy downpours are possible Saturday night into Sunday which could cause localized urban and poor drainage flooding. Otherwise, no widespread hydrologic issues are anticipated Saturday Night through early next week. && .TIDES/COASTAL FLOODING... Easterly SCA winds will likely have surges building to 1 to 1 1/2 ft during the times of high tide tonight. Generally around 3/4 to 1 1/4 ft positive departures are need to reach minor flood thresholds. As a result, widespread minor coastal flooding is expected with tonight`s high tide for vulnerable coastal locales along the south shore bays of W LI and Jamaica Bay. Meanwhile localized and brief minor flooding of vulnerable locales is expected along Lower NY Harbor and Western LI sound. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Coastal Flood Advisory from 11 PM this evening to 3 AM EDT Saturday for NYZ178-179. NJ...None. MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ330-335- 338-340-345. Small Craft Advisory until 6 PM EDT Saturday for ANZ350-353- 355. && $$ SYNOPSIS...12/NV NEAR TERM...12/DW SHORT TERM...12 LONG TERM...NV AVIATION...MD MARINE...12/NV HYDROLOGY...12/NV TIDES/COASTAL FLOODING...//

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