Area Forecast Discussion
Issued by NWS Upton, NY

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860 FXUS61 KOKX 211659 AFDOKX Area Forecast Discussion National Weather Service New York NY 1259 PM EDT Fri Jul 21 2017 .SYNOPSIS... Hot and dry conditions are expected through Saturday. A weak cold front will settle south of the area tonight. This front will remain nearly stationary across the area as waves of low pressure move along it from Saturday night through early Tuesday. High pressure will follow late Tuesday through Thursday. A cold front will approach Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Temperatures, dewpoints and cloud coverage were again slightly adjusted to better match observed trends. Locations across Southeast Connecticut and Eastern Long Island were adjusted to have slightly lower temperatures than previously forecast. Overall, the forecast remains on track. A near zonal upper flow today as a anomalously strong polar low tracks east through Northern Ontario/Quebec. At the surface, a weak surface cold front pushes south through the region today. Lack of trigger and focus, subsidence and weak capping should inhibit any convection development today. Deep W/NW flow and subsidence today will favor a sunny, hot and dry day. Temps across the coastal plain will rise into the lower 90s to 95, with upper 80s to lower 90s interior. Deep mixing and subsident NW flow should promote dewpoints at least falling into the lower to mid 60s for much of the area. Heat Advisory continues for the the NYC/NJ metro and LI, for 3rd day with heat indices in the mid 90s...with coastal Westchester and Fairfield counties included as well.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Active zonal upper flow continues during this period...with signal for PAC/convective energy approaching the region late Sat/Sat Night. At the surface, the weak cold front pushes se of the region tonight with high pressure building in from the west on Saturday. Tranquil conditions expected tonight with warm but less humid airmass than the last couple of nights. Subsidence, deep mixing, and light offshore winds will spell another mostly sunny (possibly filtered by high clouds), hot and dry day on Saturday. Highs will generally be in the upper 80s to lower 90s area wide. Dewpoints should mix down a bit more than Friday based on lower 850 TD`s; into the upper 50s/lower 60s Sunday afternoon across the interior. For coastal areas though, dewpoints may creep back towards 70 degrees with afternoon sea breeze development, while temps drop back into the 80s. It appears that heat indices will generally top out in the upper 80s/lower 90s for much of the region, but a few spots in the NYC/NJ metro could flirt with 95 degrees. Not enough confidence to extend heat advisory at this time. A this point it appears any MCS activity with the approaching shortwave will hold off until Sat Eve/Night...but the evolution of these complexes are always difficult to detail this far out. Will gradually increase slight/low chance pops from w to e late day/eve to cover timing uncertainty. Otherwise...dry conditions expected for much of the day with subsidence and capping. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... Prepare for unsettled weather from late Saturday through early Tuesday. This portion of the extended forecast will be dominated by an unseasonably south latitude polar jet orientation, with multiple short waves moving through the Northeast in northwest flow, which is typically a pattern that offers very little predictability. Despite considerable uncertainty regarding the amplitude and timing of the upper lvl short waves accompanied by their sfc reflections, this pattern remains favorable for periods of heavy rainfall and thunderstorms as multiple Mesoscale Convective Systems/MCS move across the area in northwest flow. The greatest complexity with the forecast remains on where frontal boundaries stall, which have impacts on temperature, wind, instability, cloud cover, etc, but most importantly on where exactly these systems will track. The forecast will need to be monitored over the next few days for potential heavy rain and flooding along with severe weather. An amplifying short wave is forecast to mv east of the area by early Tuesday, bringing a refreshing air mass change to a dry cool continental polar air mass during the mid week period before another front approaches toward the end of the work week. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... VFR for today on a WNW flow, with coastal/eastern terminals going more WSW later in the afternoon. Flow increases to around 10 kt late this morning and into the afternoon. For the mid to late afternoon some occasional gusts at 15-20 kt possible for city and southern coastal terminals. 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: Timing and duration of gusts may be off by an hour or two for this afternoon. The afternoon KJFK haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KLGA TAF Comments: Timing and duration of gusts may be off by an hour or two for this afternoon. The afternoon KLGA haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KEWR TAF Comments: Timing and duration of gusts may be off by an hour or two for this afternoon. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: Timing and duration of gusts may be off by an hour or two for this afternoon. KHPN TAF Comments: No unscheduled amendments expected. KISP TAF Comments: Timing and duration of gusts may be off by an hour or two for this afternoon. .OUTLOOK FOR 12Z SATURDAY THROUGH TUESDAY... .Saturday...VFR. .Saturday Night-Tuesday AM...Episodes of showers and thunderstorms with MVFR or lower conditions possible. .Tuesday PM...Conditions improving to VFR. && .MARINE...
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Although winds and seas are forecast to remain below SCA (Small Craft Advisory) levels of 25 kt and 5 ft through Saturday night, there is the potential for thunderstorms Saturday night that could result in higher waves and winds. Marine Weather Statements and/or Special Marine Warnings are possible during that time. Depending on the exact track of the stalled front, southerly swells may begin to increase through the weekend into early next week, with a low probability for SCA conditions on the ocean by early Monday. Conditions will gradually improve by mid to late week as winds decrease in building high pressure, allowing any lingering swells to slowly subside.
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&& .HYDROLOGY... Chance of heavy rain causing flooding from Saturday night through Monday as multiple waves of low pressure ride along a nearly stationary front draped across the local area. Widespread amounts of 1 to 2 inches likely; with isolated higher amounts. Estimated maximum hourly rainfall rates of at least 1 inch. && .TIDES/COASTAL FLOODING... An approaching new moon (Sun) will have tides running high this weekend into early next week. Positive tidal departures of 1/2 to 1 ft will be needed for minor flooding during the night time high tides during this time. Localized minor flooding is possible starting with the Saturday Night high tide cycle, mainly in the western south shore bays of LI. A bit more widespread minor flooding is possible Sunday Night if an e/ne flow develops ahead of an approaching frontal system. The threat for minor flooding could continue into Monday. Note: If any episodes of heavy rain coincide with the high tides, coastal urban/poor drainage flooding would be exacerbated. && .CLIMATE... Today will mark the 3rd consecutive day of 90+ degrees temps for much of the NYC/NJ urban corridor, with a 4th day likely on Saturday. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Heat Advisory until 6 PM EDT this evening for CTZ009. NY...Heat Advisory until 6 PM EDT this evening for NYZ071>075-078- 080-176>179. NJ...Heat Advisory until 6 PM EDT this evening for NJZ004-006- 104>108. MARINE...None. && $$ SYNOPSIS...GC/NV NEAR TERM...JM/NV SHORT TERM...NV LONG TERM...GC AVIATION...JE/DW MARINE...GC/NV HYDROLOGY...GC/NV TIDES/COASTAL FLOODING... CLIMATE...

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