Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 192026 AFDOKX Area Forecast Discussion National Weather Service New York NY 426 PM EDT Wed Jul 19 2017 .SYNOPSIS... Hot and humid weather will continue across the Tri-State Area through Thursday. A cold front will pass across the area Thursday night into Friday morning with showers and thunderstorms and possibly bring some brief relief from the heat. This cold front will stall south of the area late Friday and remain around through the weekend before finally moving south as a cold front early next week. High pressure follows through mid week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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A few showers popped along the Sound sea breeze across Long Island earlier this afternoon but have since dissipated. A surface pressure trough remains in place near the coast with westerly flow behind it. There is a considerable moisture gradient across the area with this trough with dewpoints in the 60s from LaGuardia on west and north, while dewpoints have held in the 70s across Long Island and eastern CT where the flow off the water has held all day. As a result, this has trimmed back the uncomfortable factor a touch, but it remains on the hot side across the area especially in and around The City. Expect a mainly clear sky tonight once any cumulus around clear out except across the East End of Long Island and in southeastern CT where enough of an onshore flow of nearly 70-75 degree water could allow for some low stratus to develop. Pesky haze has lingered at Groton all day so this should be a bellwether of things to come tonight. As temps cool toward the dewpoint with light winds, we could also see patchy fog develop on the East End of The Island, the southeast CT coast and in the interior valleys of southern CT as well as the Lower Hudson Valley and Upper Passaic County and the Ramapo River Valley in North Jersey. A sticky night especially in and near The City with lows in the mid to upper 70s with lows in the upper 60s in the coolest spots well north and west. A low risk for rip currents will continue at area beaches through this evening.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY NIGHT/... Any fog that develops overnight should dissipate after daybreak with any stratus gone by mid-morning. The surface trough along the coast will move out. A westerly flow sets up across the area ahead of an approaching cold front. This will result in another hot day with temps in the 90s even at the coast. I went with the warmer end of Guidance in areas from Newark and The City on east as the flow is offshore and usually MOS underperforms in this sort of wind regime. A Heat Advisory remains in effect for much of the area and this still looks good. Heat index values will be 95-98 across the most urbanized areas in the afternoon and early evening. The next issue comes tomorrow night as a cold front approaches from the northwest. This is a healthy front with a progged 100 kt+ jet at 250 mb moving across Upstate New York. All operational models agree on some sort of approaching MCS (mesoscale convective system) working across Upstate NY and then weakening or moving toward the Lower Hudson Valley late Thursday evening into early Friday morning. There are variations in the models in how intense and how far south this activity gets but the agreement in the models was enough to boost PoPs. There is some potential if activity is more robust for downpours and gusty winds, especially north of The City in this time frame. Once this moves through somewhat drier air heads in for Friday. It is worth noting the WRF/NAM is much lower with temps on Friday showing highs inly in the mid 80s. The NAM is cooler at 850 mb by 2-4 degrees C, but if activity is slower to exit or brings more clouds we may miss the ability to hit Heat Advisory criteria and thus we held off on extending it since it is not a slam dunk. For now, I lowered temps a hair mainly inland but kept readings in the lower 90s at the coast given the west/northwest offshore flow. The front will stall to the south Friday night but it looks dry and stable enough to remove any showers and thunderstorms from the forecast and keep things dry. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Considerable uncertainty exists for the extended as the polar jet remains at an unusually southward latitude for this time of year. A series of short waves are forecast to develop and move into the Northeast in the developing northwest flow, which is a low confidence pattern on the ultimate track of where any MCSs develop. Adding to the complexity is where the fronts will stall - at the moment forecast to be in the vicinity of the northern NJ, southeast NY and CT area. Depending on the exact location...temperatures, wind direction, instability, etc could vary significantly. Regardless, confidence is highest in a potentially wet and stormy few days as these potent waves progress southeastward, which may at times tap into steeper mid level lapse rates and bring stronger storms. There is potential for high pressure to begin to develop across the area by Tuesday night or into the mid week with cooler and drier conditions. && .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... A weak trough of low pressure remains nearly stationary in the vicinity through this evening before a weak cold front slowly approaches Thursday. Mainly VFR conditions are forecast with only exception being in any isolated showers or thunderstorms into early this evening as well as patchy fog overnight into early Thursday. Only areas where there is more confidence of lower conditions is KSWF and KGON for MVFR vsby fog. Winds will be W-NW to the northwest of KJFK and at KJFK and terminals east more SW winds are expected. A general SW flow tonight becomes light and variable overnight into early Thursday with W-SW flow developing Thursday by the late morning/afternoon. Wind speeds 10-15 kt through early evening with some gusts to 20 kt with otherwise 5-10 kt flow. 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: End time of gusts may last 1-2 hours past forecast. KLGA TAF Comments: NW flow may last an hour later than in TAF. End time of gusts may last an hour past forecast. KEWR TAF Comments: NW flow may last an hour later than in TAF. End time of gusts may last an hour past forecast. KTEB TAF Comments: NW flow may last an hour later than in TAF. End time of gusts may last an hour past forecast. KHPN TAF Comments: NW flow may last an hour later than in TAF. End time of gusts may last an hour past forecast. KISP TAF Comments: End time of gusts may last 1-2 hours past forecast. .OUTLOOK FOR 18Z THURSDAY THROUGH MONDAY... .Thursday-Friday...VFR initially for rest of Thursday afternoon. MVFR or lower with a chance of showers and thunderstorms Thursday night into Friday morning. VFR thereafter through Friday night. .Saturday...MVFR or lower possible with a chance of showers and thunderstorms. .Sunday-Monday...MVFR or lower possible with a chance of showers and thunderstorms. && .MARINE... Winds offshore at buoys have picked up to around 15 kts in gusts this afternoon as the low-level coastal jet has strengthened in response to the approaching surface trough. Waves were running near 3 feet and may get close to 4 feet briefly this evening. Patchy fog and low stratus clouds are possible tonight near the waters around the East End of Long Island and in the waters of New London County that could drop visibility to near 3 statute miles. A cold front will cross the area tomorrow night into early Friday morning bringing showers and thunderstorms. The front is expected to stall to our south late Friday. Generally dry conditions are expected through Friday night behind the front with northerly to northwesterly winds under SCA levels. 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 Monday. && .HYDROLOGY... There is a the potential for heavy rainfall producing thunderstorms across the area late Thursday evening into early Friday morning as a complex of showers and thunderstorms approaches from the northwest. This could result in pockets of heavier showers and thunderstorms that could produce rainfall totals in excess of one inch per hour. The main threat would be poor drainage flooding in highly urbanized and other poor drainage areas. There is a low chance for flooding during the Saturday Night into Monday Night period as a slow moving frontal system interacting with a moist and unstable airmass brings a threat for periods of heavy showers and thunderstorms. && .CLIMATE... Today marked the 8th day of 2017 the temperature has reached at least 90 degrees at Central Park. So far we have had two heat waves (at least 3 consecutive days of 90 degrees or greater) in 2017 at Central Park - from May 17th through May 19th and from June 11th through the 13th. The highest temp of 2017 at The Park has been 94 on June 13th. Highest temps of 2017 for the other main climate stations in the area: LaGuardia Airport: 101 on 6/13 JFK Airport: 94 on 6/13 Islip: 93 on 6/13 Newark: 99 on 6/13 Bridgeport: 94 on 6/13 && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Heat Advisory until 6 PM EDT Thursday for NYZ069>075-176>179. NJ...Heat Advisory until 6 PM EDT Thursday for NJZ004-006-103>108. MARINE...None. && $$ SYNOPSIS...MD/CS NEAR TERM...CS SHORT TERM...CS LONG TERM...MD AVIATION...JM MARINE...MD/CS HYDROLOGY...MD/CS CLIMATE...CS

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