Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 290458 AFDOKX Area Forecast Discussion National Weather Service New York NY 1258 AM EDT Sat Apr 29 2017 .SYNOPSIS... A series of weak fronts cross the region tonight into Saturday night. High pressure will return briefly for Sunday. A warm front will then approach from the south Sunday night, and lift into or through the area on Monday, followed by a cold front from the west Monday night into early Tuesday morning. Weak high pressure will return for the rest of Tuesday into Wednesday. A low pressure system will then approach on Thursday, and pass nearby on Friday. Weak high pressure then builds in through Wednesday. A frontal system approaches from the southwest Thursday and moves along the coast through late week. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Minor adjustments were made again to the forecast database to reflect the observed trends mainly with temperatures and dewpoints. Lower and thicker clouds are expected late tonight as the chances for showers and thunderstorms increase ahead of the warm front. With coherent Showalter index forecast agreement between different models with slightly negative values, elevated instability is conveyed, and hence the potential will be there for thunderstorms. The coherent mesoscale reflectivity fields show higher reflectivity forecast in the 09-12Z timeframe in the region. The forecast precipitable waters increase to near 1.6 to 1.7 inches briefly early Saturday morning with the convection so brief locally heavy rain will be possible especially with any thunderstorms. Through this evening high pressure will remain across the region as Bermuda high pressure remains in the western Atlantic. This keep a south to southwest flow across the area with increasing dew points tonight. A warm front will be developing after 03Z from low pressure across the central plains. There will be increasing lift and instability mainly aloft late tonight and into Saturday morning. In addition a weak vort will travel along the developing warm front. This is expected to trigger showers and a chance, or scattered embedded thunderstorms late tonight, after 08Z. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/... The front will remain in the area into early Saturday morning and then dissipate as the Bermuda high builds back into the area, leaving a warm and humid, summer like airmass in place. Also, the vort moves quickly east of the region by 15Z, may be sooner as depicted in some short term guidance. Afterward expect area to remain dry, although both the NAM and GFS hint at some precipitation heading close to the area late Saturday afternoon. More likely is that maybe scattered showers develop on the periphery of the high late in the day. Despite rain and clouds early in the day, high temperatures expected to be close to Friday highs, a couple of degrees lower, as sunshine develops and with mixing to 900-850 MB. The boundary, cold front then gets push south late Saturday night as high pressure builds to the north. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Remarkably consistent trend to the long term, so changes to the previous forecast have been minor at most, except perhaps for Sunday into Monday. Temps have trended a little cooler for Sunday after the back door cold frontal passage, with highs from the upper 50s to mid 60s, warmest west of the Hudson. Precip with the approaching warm front looks to be on the light side, but do expect widespread low clouds to develop, also some patchy fog late Sunday night into Monday morning just ahead of the warm front. Depending on the strength of a lobe of high pressure off to the east and the potential for a weak wave of low pressure to develop along the front, it may take some time for the front to lift north of the area, especially across Long Island and southern CT, so there will be a wide range of potential high temps on Monday. High temp forecast is close to the 00Z ECMWF ensemble mean MOS, with 60s across southern CT and most of Long Island, and 70s west of there. That said, the high end ensemble numbers suggest lower 80s are possible west of the Hudson, and widespread 70s farther east, if the front lifts through by afternoon. At any rate, a cold front should move through Monday night into early Tuesday morning with showers and a few thunderstorms, followed by dry wx for the rest of Tue into Wed, with temps running above average especially on Tue, with upper 60s to mid 70s, then mid and upper 60s on Wed. As noted a couple of days back, chances for rain will increase late this week as flow aloft becomes zonal at first, then more amplified via a developing upper trough in the Central states. The resulting deep layer SW flow in its advance should result in surface cyclogenesis along a baroclinic zone over the southern Plains and lower Mississippi Valley, with this low then moving up the coast toward the area and tapping into Gulf and Atlantic moisture. This has some potential to be a heavy rain maker on Friday if the synoptic scale ingredients are in sync, but it is still too early to know for certain. && .AVIATION /06Z SATURDAY THROUGH WEDNESDAY/... A weak cold front settles over the area tonight...with a wave of pressure moving through early Saturday morning. The cold front slowly sags south of the region late Saturday. An area of showers with embedded tsra will approach from the west overnight, and should pass through from 8-14Z, west to east. Medium to high confidence in sparse coverage of tstms...conveyed through a VCTS. The other concern is potential for IFR/LIFR stratus/fog...currently lurking offshore...working back into KJFK/KISP/KGON after 06z. Elsewhere MVFR or IFR conditions are possible in fog and showers late tonight into Sat morning. Once these showers move through by late Sat morning, VFR conditions will return. Light s or variable winds overnight...eventually turn toward the W/SW by late morning Saturday. Westerly gusts to 25-30 kt likely for KLGA/KEWR/KTEB/KSWF Sat aft. South coastal terminals likely to see winds backed more to the SW...with gusts 20 to 25 kt in the afternoon. Winds should eventually veer to wnw late Saturday. .OUTLOOK FOR 00Z SUNDAY THROUGH WEDNESDAY... .Saturday Night-Sunday...VFR...then MVFR cigs possible late Sunday. Winds veering from NW to E/NE Sat night. E/SE gusts 15 to 20 kt Sun aft. .Sunday night-Monday...MVFR or lower possible in showers and fog. .Monday night...MVFR in showers/possible thunderstorms. LLWS possible. .Tuesday-Wednesday...VFR. && .MARINE...
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Long period south to southeast swell between 3 and 5 feet continues on the ocean waters. The combination of wind wave and swell was allowing for seas to still fluctuate around 5 feet mainly on the waters east of Fire Island Inlet. Seas and swell will be slow to subside tonight and could fluctuate between 4 and 5 feet. The small craft advisory for hazardous seas remains in effect until 09Z for the waters east of Fire Island Inlet. Winds and seas will then be below advisory levels until later Saturday afternoon as a south to southwest flow strengthens and seas build once again on the ocean waters. Then seas subside Saturday evening as winds diminish. With the current small craft advisory in effect will not issue one for Saturday at this time. Increasing easterly flow between a warm front approaching from the south and high pressure off to the northeast could push ocean seas up to 5 ft late day Sunday into Sunday evening. Still high confidence in increasing S-SW flow pushing ocean seas above 5 ft early next week, most likely by Mon night head of a cold front, and lasting into at least Tue night if not Wed as moderate post-frontal WSW flow continues. Could see gusts up to 25 kt there late Mon night into Tue afternoon, with seas peaking at 5-7 ft Tue morning.
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&& .HYDROLOGY... No hydrologic impacts are expected through Thursday. A low pressure system approaching from the southwest could offer potential for heavy rain and hydrologic impact on Friday, but it is too early to know for certain. && .OKX WATCHES/WARNINGS/ADVISORIES...
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CT...None. NY...None. NJ...None. MARINE...Small Craft Advisory for hazardous seas until 5 AM EDT early this morning for ANZ350-353.
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