Area Forecast Discussion
Issued by NWS Upton, NY

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498 FXUS61 KOKX 272200 AFDOKX Area Forecast Discussion National Weather Service New York NY 600 PM EDT Thu Jul 27 2017 .SYNOPSIS... A weak cold front moves across the region from central New York overnight before stalling just south of Long Island on Friday. Waves of low pressure develop along the front Friday night into early next week. By mid next week, the low pressure area moves farther offshore with weak high pressure building in from the west. Weak high pressure remains over the area until Thursday next week when a cold front approaches from the northwest. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Light showers over the region with weak warm advection. Much of this is east of the region by 22Z. The next round of showers over upstate NY, which appear more associated with the weak front passes mainly over eastern section as the HRRR continues to insist upon. We do have a slight chance for Thunder overnight as HRRR soundings indicate LI`s of -2 C and up to a 1000 J/KG on MU CAPE. Not very confident in this as there been zero lightning so far today. There will be a moderate risk of rip currents at area beaches. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SATURDAY/... The front settles just south of Long Island on Friday and have gone with a dry, but cloudy, forecast. Over running sets up Friday evening as cyclogenesis begins as shortwave over the Great Lakes closes off. This cause rapid deepening of the surface low over the DelMarVa. The upper dynamics cause the surface low to sag south as wave "spin off" to the east. Main potential hazard is heavy rain. Having looked at a lot of guidance, we have sided with the idea that the heaviest rain stays south of our region and will not issue a flood watch - at least not yet. In fact just saw the 15Z SREF and amounts are down. HWO (Hazardous Weather Outlook) continue to highlight for the potential for flooding - but the potential is still in the low chance level. See Hydro section to see rainfall forecast amounts. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... The upper level trough remains over much of the Eastern U.S. for the remainder of the weekend. The trough axis will slowly move east during this time but will still be west of the local region. The local region will be near the inflection point of this trough. The upper level jet stream affiliated with the trough will be situated generally from the western Atlantic waters not that far offshore northeast through Nova Scotia. This will help sustain the low pressure along the stalled front at the surface. The region will remain in a northeast flow as a result. The pressure gradient will still be relatively tight Saturday night, making for gusty winds mostly between 30 and 40 mph. Winds decrease Sunday into Sunday night as low pressure becomes weaker south of Long Island, hence weakening the pressure gradient. The winds finally switch in direction mid to late next week. More typical southwest flow will come into place during this timeframe. In terms of weather, cooler than normal temperatures and rain will still be in the forecast Saturday night and Sunday, albeit mostly light rain. Higher chances for the light rain will be across Long Island and offshore while lower chances will be farther north. Rain could even linger especially across Long Island going into Monday and Tuesday of next week as some models convey a retrograding movement back to the west of the offshore low. There are even some slight increases in elevated instability, making for a slight chance of thunderstorms on the East End of Long Island Monday night into early Tuesday. Drier conditions and temperatures closer to normal return Tuesday and more so for mid to late next week. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/...
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A weakening cold front slowly crosses the area into Friday morning. Low pressure begins to develop over the central Appalachians by early Friday afternoon. City terminals will see conditions vary between MVFR and VFR into this evening, then ceilings lift to around 20,000 FT overnight. Elsewhere mainly MVFR conditions (with pockets of VFR) become MVFR throughout by midnight. IFR conditions are probable at CT/Long Island terminals and KHPN overnight. Conditions improve to VFR everywhere by around 12Z Friday. Winds become light and variable throughout this evening. 5 to 10 kt this afternoon become light and variable overnight. NE-E winds at under 10kt develop at eastern terminals and possibly KLGA/KJFK by mid Friday morning. 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 MVFR ceilings are possible into this evening. KLGA TAF Comments: Occasional MVFR ceilings are possible into this evening. KEWR TAF Comments: Occasional MVFR ceilings are possible into this evening. KTEB TAF Comments: Occasional MVFR ceilings are possible into this evening. KHPN TAF Comments: Occasional VFR ceilings are possible into this evening. KISP TAF Comments: Occasional VFR ceilings are possible into this evening. .OUTLOOK FOR 18Z FRIDAY THROUGH TUESDAY... .Friday Afternoon...VFR. .Friday night-Saturday...MVFR or lower with heavy rain and possibly a tstm. NE winds G25-35kt on Saturday, mainly at the coastal terminals. .Saturday night-Tuesday...VFR.
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&& .MARINE... Gale watch in effect for Saturday. Tranquil though Friday afternoon, then low pressure to the south increase NE winds with gales forces gusts likely on Saturday. As a result, seas build rapidly on all waters. Active time period to start Saturday night with gales probable across the waters due to a relatively tight pressure gradient. The gales could even extend on the ocean into Sunday with otherwise SCA winds Sunday morning. The SCA winds are forecast for most waters Sunday afternoon and evening. Then for non-ocean waters, there will be sub SCA conditions. For the ocean, both winds and seas are forecast to be in SCA range late Sunday night through Monday evening. Thereafter though, ocean seas are forecast to still be meeting low end SCA with 5-6 ft values. && .HYDROLOGY... There is the potential for a heavy rainfall event Friday night through Saturday, especially across portions of northeastern New Jersey, New York City and Long Island. From Friday night through Saturday night rainfall is expected to range from around 1/2 to 3/4 of an inch across the Lower Hudson Valley and interior southern Connecticut to 1 to 2 inches across northeastern New Jersey and across Long Island. There is though the potential for significantly higher amounts if the pattern moves heavier rainfall from central and southern && .TIDES/COASTAL FLOODING... Despite the expected strong Northeast winds on Saturday, only minor coastal flooding appears possible on the south shore bays of western Long Island at this time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...Gale Watch from Saturday morning through late Saturday night for ANZ330-335-338-340-345-350-353-355. && $$ SYNOPSIS...Tongue NEAR TERM...Tongue SHORT TERM...Tongue LONG TERM...JM AVIATION...Maloit/DW MARINE...JM/Tongue HYDROLOGY...Tongue TIDES/COASTAL FLOODING...

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