Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 171605 AFDOKX Area Forecast Discussion National Weather Service New York NY 1205 PM EDT Tue Jul 17 2018 .SYNOPSIS... A slow moving frontal system will move through the region late this afternoon into tonight. High pressure will build across the region Wednesday through Thursday, pushing offshore late Friday. A frontal system will impact the region for the second half of the weekend into the beginning of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Stratus continues to be stubborn across southern and eastern portions of Long Island. In addition, there has been some westward expansion along close to the NJ coast which could impacts western portions of Long Island. The airmass is very moist and mixing is very shallow until convection starts working into the area this afternoon. There is considerably more sun for areas outside of the stratus. A northern stream trough extending down through Hudsons Bay into the northern Great Lakes this morning, will gradually slide east into the eastern Great Lakes by this evening. At the surface, a slow moving cold front over Western NY this morning, will slide into western portions of the Tri-State by this evening and then east of the region by late tonight. This front will be the focus for numerous showers and thunderstorms late this morning into early afternoon across Central PA/NY, which should continue to slide into western portions of the Tri-State region later this afternoon with a moist and moderately unstable airmass in place, and then to the coast this evening. Before then, CAMS indicate discrete convection could develop this afternoon along the sea breeze boundary across or just to the NW of the NYC metro, off elevated terrain of the NW hills, and/or off any resultant outflow boundaries this afternoon. Main threat as advertised the last couple of days will be for torrential downpours and a flash flood threat from any training convection. A favorable moist and unstable environment exists for deep convection and heavy rainfall, marked by narrow but tall CAPE profiles, surface dewpoints in the lower/mid 70s, PWATS of 2-3 std above normal (2.25-2.5"), and a warm cloud layer depth of 13-15 KFT. Limiting factor for widespread flash flooding will be 25-30 kt of steering flow with any discrete convection, and then eventual cold pool formation along developing linear convection ahead of the cold front, providing sufficient forward propagation through the region. FFA remains in effect for NE NJ, NYC metro and surroundings, as well as SW CT, where modest potential exits for both SW to NE training discrete cells this afternoon, and then a linear convective line ahead of the cold front late this afternoon into evening. See hydrology section for more information on impacts. The other threat is potential for a few strong to severe storms across NYC metro and surroundings, NE NJ, Lower Hudson and SW CT in a moderately unstable environment with thin/tall CAPE, but generally weak to marginally sheared environment. As a result, wet microbursts would be the main threat, either with discrete or linear convective modes this afternoon into early evening. Increasing high clouds late morning and afternoon will be limiting factor to maximizing temps across the NYC metro and interior, while a strengthening southerly flow and more of a maritime tropical airmass along the coast should hold temps a bit cooler than yesterday. Dewpoints are expected to be slightly higher than yesterday through, with moisture pooling into the lower to mid 70s likely. Highest confidence in several hours of 95 heat indices continues for NE NJ and NYC metro with temps quickly climbing into upper 80s with lower to mid 70s dewpoints. Potential exists for 95 heat index to be briefly hit for a second day across Nassau and Western Suffolk counties away from the south coasts, as well as parts of the CT and Lower Hud River Valleys before any convection/sea breeze, but not high enough confidence in marginal occurrence due to above factors to expand heat advisory. A high risk of rip currents exists for the ocean beaches today into this evening due a 15 to 20 kt southerly flow producing 5 ft southerly wind waves, combined with a SE 2ft@8 sec swell.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Mean troughing over the region, as trough axis slides into the region tonight and then through on Wednesday, with a second shortwave axis approaching Wed evening. At the surface, cold front pushes east through the region this evening, with linear convective line likely pushing east through the region. Additional shower and embedded thunderstorms activity could be occurring as the cold front slowly moves through through by 2 am or so, but waning instability and possible surface wave development south of the region should have this activity becoming more stratiform as the evening progresses. Drying conditions expected in wake of the front on N/NW flow late tonight into Wednesday. Highs in the mid to upper 80s with mostly sunny skies (outside of cirrus and few-sct aft cu) expected on Wed, but much more comfortable humidity levels as dewpoints drop into the 50s. A moderate to locally high risk of rip currents exists on Wednesday due to residual 3-4 ft @ 7 sec southerly swells, combined with 2 ft @ 9 sec SE swells. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... High pressure will continue to build in at the surface while in the upper levels, a trough will cross the area Wednesday night with the trough axis pushing off shore Thursday. A backing wind profile is noted in the forecast soundings for Thursday, so Thursday will likely be slightly cooler than Wednesday, with at highs at or just below normal for this time of year: in the lower to middle 80s. A continued northerly flow will keep humidity levels in a comfortable range for most people as dew points will be in the 50s for the entire area. Some upper 40s dew point readings possible in northeast New Jersey. High pressure pushes off the New England coast late on Friday, while in the upper levels a ridge moves over the area Thursday night into Friday. With some height rises and a veering profile in the forecast soundings for Friday, temperatures will be generally be a couple of degrees warmer than on Thursday. Humidity levels will increase somewhat as dew points rise into the upper 50s to lower 60s. Saturday will continue to be dry with high pressure off the New England coast. Humidity levels continue to increase with dew points rising well into the 60s. An old frontal boundary to our southwest will head northeast during the day as low pressure over the Western Great Lakes region slowly moves east. The second half of the weekend will be unsettled, which will likely last into the beginning of the new work week as a blocked pattern sets up. There is a good deal of uncertainty with the operational models at this point, especially with any disturbances/low pressure systems that may develop along the approaching warm front and the track of the parent low over the Great Lakes region. && .AVIATION /16Z TUESDAY THROUGH SATURDAY/...
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High Impact Day today with Numerous Showers and Thunderstorms in the Afternoon A cold front approaches today, moving through the terminals late in the afternoon, into early evening. Stratus has developed across much of the area. Daytime heating will allow the deck to gradually lift/dissipate into the early afternoon, so TEMPOs are in place with the expectation that stratus may be more occasional through the early afternoon. Stratus will be more persistent at KGON/KISP through the early afternoon. Then, scattered showers develop into the early afternoon, followed by a line of thunderstorms that will move across the area during the mid to late portion of the afternoon. The line will move west to east. MVFR/IFR conditions and gusty winds of 30-35 kt are possible in the stronger thunderstorms. Heavy downpours could lower visibility to LIFR briefly if any individual storm passes over a terminal. A few showers and thunderstorms may linger into the evening hours as well, then clearing should take place after midnight. S to SW winds 5 to 10 kt increase to 10 to 15 kt, with occasional gusts up to 20 kt possible. Winds lighten and become variable as the front slowly passes late this afternoon/early evening. Winds eventually turn to the NW late this evening and overnight, under 10 kt. 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 stratus possible through around 18Z. Amendments for the timing of showers and thunderstorms are likely this afternoon and evening. The afternoon KJFK haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KLGA TAF Comments: Occasional MVFR stratus possible through around 18Z. Amendments for the timing of showers and thunderstorms are likely this afternoon and evening. The afternoon KLGA haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KEWR TAF Comments: Occasional MVFR stratus possible through around 18Z. Amendments for the timing of showers and thunderstorms are likely this afternoon and evening. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Occasional MVFR stratus possible through around 18Z. Amendments for the timing of showers and thunderstorms are likely this afternoon and evening. KHPN TAF Comments: Occasional MVFR stratus possible through around 18Z. Amendments for the timing of showers and thunderstorms are likely this afternoon and evening. KISP TAF Comments: Stratus may be slow to lift. Amendments for the timing of improvement to VFR and showers and thunderstorms are likely late this afternoon and evening. .OUTLOOK FOR 12Z WEDNESDAY THROUGH SATURDAY... .Wednesday-Saturday...VFR.
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&& .MARINE... Ocean seas tonight so far remain near 3 ft with gusts between 15-20 kt over the ocean and less over the non-ocean waters. The forecast remains mainly on track. Sub-SCA conditions continue to prevail tonight with light winds and seas below 5 ft. Winds and seas then increase Tuesday ahead of a cold front. SCA conds expected on the ocean waters by mid- morning and lasting into Tuesday night. Winds and seas will remain below SCA criteria Wed Night through Saturday morning. Seas will build on a southerly flow on the ocean waters Saturday, with 5 ft waves forecast by Saturday night. Right now, only a brief period of 5 ft waves is forecast, with waves diminishing to below 5 ft by Sunday. Wind gusts should remain below 25 kt through the weekend. However, with a complex frontal system forecast to affect the waters by Sunday, there is a good deal of uncertainty with the wave and wind forecast. && .HYDROLOGY... A slow moving frontal system will bring numerous showers and thunderstorms to the region this afternoon into this evening. Any thunderstorms will have the potential to bring torrential downpours with rainfall rates of 1 to 2 inches per hour. These types of rainfall rates will cause urban and poor drainage flooding, with potential for flash flooding in areas affected by multiple successive thunderstorms. Additionally, rapid water level rises can occur on flashy small rivers and streams in basins affected by this activity. Basin average rainfall will likely vary from 1/2 inch to 1 1/2 inches, with isolated amounts of 2 to 4 inches possible. FFA remains in effect for NE NJ, NYC metro and surroundings, as well as SW CT, where potential exits for both SW to NE training discrete cells this afternoon, and then a linear convective line ahead of the cold front late this afternoon into evening. A potential blocking pattern late next weekend could set up an extended period of unsettled weather through the beginning of next week. Right now, due to uncertainty this far out, there is a low chance of seeing any flooding. && .EQUIPMENT... NYC NOAA Weather Radio Station KWO-35 (162.55 MHz) remains off the air for an extended period of time. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...Flash Flood Watch until 10 PM EDT this evening for CTZ005>007- 009-010. NY...Flash Flood Watch until 10 PM EDT this evening for NYZ069>075- 176>179. Heat Advisory until 6 PM EDT this evening for NYZ072>075-176- 178. High Rip Current Risk until 9 PM EDT this evening for NYZ075- 080-081-178-179. NJ...Flash Flood Watch until 10 PM EDT this evening for NJZ002-004- 006-103>108. Heat Advisory until 6 PM EDT this evening for NJZ004-006- 103>108. MARINE...Small Craft Advisory until midnight EDT tonight for ANZ353-355. Small Craft Advisory until 6 AM EDT Wednesday for ANZ350. && $$ SYNOPSIS...JP/NV NEAR TERM...NV/DW SHORT TERM...NV LONG TERM...JP AVIATION...MD/PW MARINE...JP/NV HYDROLOGY...JP/NV EQUIPMENT...

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