Area Forecast Discussion
Issued by NWS Upton, NY

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047 FXUS61 KOKX 270800 AFDOKX Area Forecast Discussion National Weather Service New York NY 400 AM EDT Tue Jun 27 2017 .SYNOPSIS...
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A cold frontal passage occurs tonight. 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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Upr lvl low shows up on stlt e of Detroit this mrng. The system will continue to track ewd today, then drift newd tngt. The associated cool front tracking across OH will reach the cwa tngt and pass offshore by sunrise Wed. All of the models are in good agreement with this soln. Radar indicates shwrs and tstms still firing from sern PA to NJ. Water vapor suggests the dynamics are sufficient for this to continue thru the mrng and expand into the swrn portion of the fcst area thru 12z. The NAM, GFS and ECMWF all support this scenario. After the first round of shwrs and embedded tstms this mrng, lapse rates steepen as the h5 trof axis approaches, and with a 120kt jet streak passing thru, isold-sct shwrs and tstms are fcst today before ending this eve as subsidence develops. The nearly dry adiabatic lapse rates up to h85 indicate a potential downburst scenario with the deepest convection. In addition, around 1500 J/kg of sbcape progged by the NAM in balanced by a brn around 35 and an el blw 30k ft could allow for mini supercells. This would produce a hail threat, particularly with any dry air intrusion abv h7 which the NAM predicts. The limiting factor for tstm development this aftn, especially the srn half of the cwa, is the amount of subsidence in the wake of convection this mrng which could suppress later development. Mainly clr in the wake of the upr trof tngt similar to the current stlt over the midwest. Temps were a blend of guidance which was in good agreement. There is a mdt risk for rip current development today.
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&& .SHORT TERM /WEDNESDAY/...
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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.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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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. Another chance but only slight chance of showers and thunderstorms is forecast for early next week with frontal boundary possibly lingering not too far away to the south of the region. 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.
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&& .AVIATION /07Z TUESDAY THROUGH SATURDAY/... VFR through the TAF period. A trough of low pressure passes across the terminals early this morning, followed by another one on Tuesday. Winds are a bit uncertain through the middle morning hours. However, speeds are expected to be less than 10 kt. Winds should veer to the W or NW in the next few hours over the city terminals with light and variable elsewhere. Winds will then gradually become southerly into the morning 10 kt or less. Winds veer to the SW into the afternoon and evening 10-15 kt, then to the W-WNW overnight around 10 kt. A few showers are possible early this morning, 08-11z over NYC terminals, and 10-13z Long Island and southern Connecticut terminals. An isolated shower/thunderstorm is also possible this afternoon. .OUTLOOK FOR 06Z WEDNESDAY THROUGH SATURDAY... .Tuesday Night-Wednesday...VFR. .Thursday...VFR. Chance of a late day shower/thunderstorm. .Friday and Saturday...MVFR or lower possible in showers and thunderstorms. && .MARINE...
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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, widespread for just about all waters, higher wind gusts near 25kt are forecast, 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.
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&& .HYDROLOGY... No hydrologic impacts expected through the beginning of next week. && .TIDES/COASTAL FLOODING...
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Astronomical tides are still running high with a low chance of any minor coastal flooding across the south shore back bays of Nassau county with the high tide cycle tngt. The water levels would only be expected to touch the minor benchmarks at just a couple of gages at most so no statement has been issued.
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&& .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...JMC SHORT TERM...JMC LONG TERM...JM AVIATION...DS MARINE...JMC/JM HYDROLOGY...JMC/JM TIDES/COASTAL FLOODING...JMC EQUIPMENT...

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