Area Forecast Discussion
Issued by NWS Upton, NY

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000 FXUS61 KOKX 191141 AFDOKX Area Forecast Discussion National Weather Service New York NY 741 AM EDT Wed Jul 19 2017 .SYNOPSIS... A weak trough of low pressure remains nearly stationary in the vicinity of the area through this evening. A weak cold front moves southeast stalling across the area Thursday through Saturday. It returns north as a warm front Sunday, followed by a cold front Monday. High pressure will return by late Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Minor changes were made to reflect the latest observations and near term forecast trends. A low lvl SW wind component has prevented the stratus clouds and fog that developed across SE CT and the east end of Long Island from spreading west along the coast. The area will remain in a deep maritime tropical air mass that will be heating into the 90s as SW winds continue circulating around the offshore high pressure system. A Heat Advisory was issued for the NYC Metro area from 11 am today/coincident with the start of the Air Quality Alerts. Day time highs in the low 90s combined dew point temps around 70 will produce heat index values in the upper 90s across the advisory area, which is forecast to continue through Thursday. For potential showers and TSTMs, today`s triggers include sea breeze fronts along the coast and re-formation of the thermal lee side trough for this afternoon. Included 20 pct POPs for these weak triggers. Note that any showers or TSTMs that do form can produce hvy downpours with local urban flooding. Precipitable water contents are arnd 1.5 inches. There is a low risk of rip current development this morning, which may become moderate for the beaches of Queens and Nassau County late today with moderate coastal jet development. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Any convection that develops should quickly dissipate with the ending of day time heating, leaving another very warm and humid night with temps in the 70s. A weak cold front will stall and become nearly stationary just south of the area Thursday. West winds behind this front will aid downslope causing temps to rise into the mid 90s across urban areas on Thursday, before weak sea breezes develop once again Thursday afternoon. With slightly lower humidity, heat index values are once again forecast to rise into the upper 90s. The heat advisory will be continued until 6 pm Thursday and may need to be further extended into Friday. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... An active near zonal flow will exist late week through the weekend as a anomalously strong polar low tracks through Northern Ontario/Quebec. This will be followed by an approaching PAC shortwave and troughing for early next week. A weak cold front approaches Thursday Night as the first in a series of shortwaves tracks through the NE in the developing zonal flow. Models are signaling potential for an MCS to track into the region late Thu Night into Friday morning with shortwave energy rounding periphery of southern ridge...but low predictability on details at this point. Otherwise...the weak cold front appears to push through the region Friday, but subsidence in deep wnw flow Friday will likely result in hot and dry conditions. The region will lie in an active zonal flow this weekend between polar low to the north and broad southern ridging, while a frontal boundary resides near the region. Models in decent agreement with the front pushing south Fri Night and remaining to the south through Saturday. This would keep the region mainly dry on Saturday with the axis of convective activity farther south...but will have to watch for any MCS activity. As PAC shortwave energy begins to dig towards the Great lakes Sat Night into Sun Night...associated low pressure/s will begin to push the stationary front through the region as a warm front Sat Night into Sunday NIght. The presence of shortwave energy moving through aloft, and a surface boundary interacting with an increasingly moist and unstable airmass, will bring an increased threat for shower and thunderstorm activity during this time. Uncertainty on how quickly this front moves north as this time. Good agreement on the shortwave trough over the Great Lakes continuing to approach the region Monday and then across the region Tuesday. The associated frontal system slowly moves through the region Monday into Monday Night with shower and thunderstorm activity. Thereafter...a cooler and drier Canadian airmass appears poised to advect into the region behind the front. Temperatures through Sat should be above normal (well into the 80 to lower 90s). This could be the 4th consecutive day of 90 degree temps for the urban corridor, although slightly lower dewpoints may make for marginal heat advisory conditions of 95 degrees. Lower confidence on temp forecast for Sun and Mon based on frontal placement and convection, but near to above seasonable temps appear likely. Temps on Tuesday may fall to below seasonable levels in a cool Canadian airmass behind the cold front. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/...
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High pressure remains over the western Atlantic as a trough of low pressure sits over the area today. Mainly VFR through the TAF period. Some fog/stratus remains at KGON. Conditions at KGON should improve to VFR between 13-14Z. There is a chance that some shower or thunderstorms develop this afternoon. Any storms that develop may briefly lower conditions below VFR. Timing and placement of any storms are too low to include in the TAF at this time. Light South/Southwest winds increase today with 10-15 kt sustained, gusting to near 20 kt. Winds become light and variable once again tonight. 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: Medium to high confidence forecast. The afternoon KJFK haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KLGA TAF Comments: Medium to high confidence forecast. The afternoon KLGA haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KEWR TAF Comments: Medium to high confidence forecast. The afternoon KEWR haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KTEB TAF Comments: Medium to high confidence forecast. KHPN TAF Comments: Medium to high confidence forecast. KISP TAF Comments: Medium to high confidence forecast. .OUTLOOK FOR 12Z THURSDAY THROUGH SUNDAY... .Thursday-Friday...VFR. .Saturday...MVFR or lower possible with a chance of showers and thunderstorms. .Sunday...MVFR or lower possible with a chance of showers and thunderstorms.
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&& .MARINE... With a warm and humid airmass across the waters, visibilities will lower as areas of fog develop through early morning. At this time will not bring visibilities below 1 nautical mile. SW winds and seas will increase late this afternoon through this evening with the approach of a weak cold front late tonight. SW winds 15-20 kt and seas arnd 4 ft will approach but not meet Small Craft Advisory/SCA levels during this time. Otherwise, a weak pressure gradient over the region will keep winds 10-15 kt or less, and keep seas below SCA levels through Saturday. Southerly swells should begin to increase Sunday into Monday ahead of an approaching frontal system, with a low probability for SCA conditions on the ocean by Monday. && .HYDROLOGY... Isolated urban flooding is possible in brief heavy downpours today. 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. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...Heat Advisory from 11 AM this morning to 6 PM EDT Thursday for NYZ069>075-176>179. NJ...Heat Advisory from 11 AM this morning to 6 PM EDT Thursday for NJZ004-006-103>108. MARINE...None. && $$ SYNOPSIS...GC/NV NEAR TERM...GC SHORT TERM...GC LONG TERM...NV AVIATION...BC MARINE...GC/NV HYDROLOGY...GC/NV

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