Area Forecast Discussion
Issued by NWS Upton, NY

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686 FXUS61 KOKX 271753 AFDOKX Area Forecast Discussion National Weather Service New York NY 153 PM EDT Tue Jun 27 2017 .SYNOPSIS... A cold frontal passage occurs this evening. A Bermuda high sets up Wednesday night. Then a frontal system passes north of the region Thursday through Friday night. A cold front approaches Saturday and moves across Sunday into Sunday night. The front may linger south of the region early next week with otherwise weak high pressure returning. && .NEAR TERM /THROUGH TONIGHT/... Potential for isolated strong to severe convection this afternoon. Best large scale lift is passing to the east of the area early this afternoon with an upper jet and mid level short wave. The forecast dilemma for this afternoon is with continued destabilization of the airmass due to approach of the upper trough, and whether it will be sufficient enough to offset subsidence and drying low levels. Have maintained scattered showers and thunderstorms this afternoon into early this evening with a pre-frontal trough/weak cold front. Deep-layer shear values of 50-60 kt and moderate instability will support low-topped supercells. Isolated thunderstorm wind damage and large hail are also a possibility this afternoon, especially across the interior where steeper low-level lapse rates will be present. The limiting factor for large hail is that thunderstorms will be low-topped. Cold front moves east of the area this evening with perhaps a few showers or thunderstorms across eastern Long Island and southeast Connecticut, otherwise it will be another dry, seasonably cool night. There is a moderate risk for rip current development today. && .SHORT TERM /WEDNESDAY/... Despite very steep low lvl lapse rates, subsidence should keep the area dry. There could be some flat cumulus, however with condensation pres deficits around 40, even this may be difficult, especially away from any terrain enhancement. Despite the cool airmass aloft, deep mixing will allow for highs to be only a few degrees blw average. A blend of guidance was used for this. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... The jet lifts north of the region and stays north of the region midweek going through much of the weekend. It starts to move farther south into the region Sunday afternoon into Sunday night, before lifting back north of the region early next week. The mid and upper level flow transitions to more of a zonal flow mid into late week and then transitions to more of a ridging pattern going into the weekend. Shortwave approaches for second half of weekend, presenting more of a trough pattern and SW flow aloft, before returning to a quasi-zonal flow early next week. High pressure moves off into the Western Atlantic, building Wednesday night, and then slowly drifting farther out to sea through Thursday night. Meanwhile, a warm front moves north of the Great Lakes and into Northern New England Thursday into Thursday night. There is a trailing cold front to the west that looks to weaken Thursday night before moving northward as a warm front Friday into Friday night. A cold front from the west approaches Saturday and moves across Sunday into Sunday night. Possibly this could get delayed as shown by the ECMWF, hence the longer time window stated for its passage. The frontal boundary of the weakening cold front Thursday night into Friday is forecast to be close enough to warrant a chance of a shower or thunderstorm. The chance continues into Friday night. The next chance of showers and thunderstorms will be this weekend. There will be a slight chance of showers and thunderstorms forecast for early next week with frontal boundary possibly lingering not too far away to the south of the region. Not expecting a total washout as coverage is expected to be mainly isolated to scattered. The showers and thunderstorms will be driven by the diurnal heat and the instability that generates. Temperatures start off near normal Wednesday night and Thursday but then trend warmer for the rest of the forecast period. It will be getting warmer and more humid. The temperatures will average about 3- 5 degrees above normal. Temperatures are forecast to be well into the 80s Thursday through Monday with some locations in the NY Metro and Northeast NJ reaching near 90 for Friday and Saturday. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... Mainly VFR as a trough of low pressure passes across the terminals late this afternoon and evening. High pressure builds south of the region on Wednesday. A southerly flow has developed across the region with speeds 10-15 kt. The wind direction will gradually veering to the SW by late afternoon and evening. Winds become W-WNW overnight 10 kt or less. A westerly flow will develop on Wednesday. showers along with isolated thunder will be possible this afternoon. Any storms could result in gusty winds and a reduction in visibility from heavy rain. ...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: Amendments may be possible for afternoon showers. An occasional gust 18-20 kt possible in the afternoon. KLGA TAF Comments: Amendments may be possible for afternoon showers. An occasional gust 18-20 kt possible in the afternoon. KEWR TAF Comments: Amendments may be possible for afternoon showers. An occasional gust 18-20 kt possible in the afternoon. KTEB TAF Comments: Amendments may be possible for afternoon showers. An occasional gust 18-20 kt possible in the afternoon. KHPN TAF Comments: Amendments may be possible for afternoon showers. An occasional gust 18-20 kt possible in the afternoon. KISP TAF Comments: An occasional gusts up to 20 kt possible this afternoon. .OUTLOOK FOR 18Z WEDNESDAY THROUGH SUNDAY... .Wednesday afternoon...VFR. .Thursday...VFR. Chance of a late day shower/thunderstorm. .Friday through Sunday...MVFR or lower possible in showers and thunderstorms. && .MARINE... Winds and seas are progged to remain blw sca lvls thru Wed. Sub SCA conditions are expected Wednesday night. Then SCA becomes more probable Thursday through Friday night for the ocean with seas reaching between 5-7 ft for much of the time. Wind gusts reach 25-30 kt much of the timeframe as well. Also during Thursday and Thursday night, higher wind gusts near 25kt will be more widespread for just about all waters, with hence probable SCA conditions for all waters. Ocean seas are forecast to linger in SCA range Saturday with waves near 5 ft particularly east of Fire Island Inlet. Much of the remainder of the weekend will have sub SCA conditions forecast. && .HYDROLOGY... No hydrologic impacts expected through the beginning of next week. && .EQUIPMENT... Observations from KFRG (Farmingdale, NY) are not available. Observations from KHPN (White Plains NY) and KHVN (New Haven CT) are being disseminated through backup methods. All is due to an FAA communication line outage. Return to service time is unknown. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...JMC/JM NEAR TERM...DW SHORT TERM...JMC LONG TERM...JM AVIATION...BC MARINE...JMC/JM HYDROLOGY...JMC/JM EQUIPMENT...

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