Area Forecast Discussion
Issued by NWS Upton, NY

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622 FXUS61 KOKX 271628 AFDOKX Area Forecast Discussion National Weather Service New York NY 1228 PM EDT Thu Jul 27 2017 .SYNOPSIS... High pressure will remain off the coast today, while a cold front slowly approaches from the northwest. The front will enter the area tonight and become stationary on Friday. Low pressure developing late Friday into Friday night over the Ohio Valley to the Mid Atlantic coast will move slowly south of the region Saturday into Saturday night. Canadian high pressure will build in from Sunday into the middle of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1230 PM Update: Well - as said previously... a challenging forecast for late afternoon/early evening. Have updated based on Radar trends and advection. Convective showers are moving into Central CT/the lower Hudson Valley and eastern PA as of 1615Z. Pure advection brings this to NYC/Long Island by 18Z. With HRRR struggling with the NOW- TERM, have updated POPs to likely for this afternoon. Instability is marginal at best with MLCAPE only about 500 J/kg and deep layer shear of 30 KT. Going with slight chance of TSTMs as a result. High temps should be in the upper 70s/lower 80s, slightly warmer than a MOS blend and still a few deg below avg. There will be a moderate risk of rip currents at area beaches.
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1230 PM Update: No changes at this time. Have updated the HWO product, but planning to hold off on a Flood Watch (would be overnight Friday into Saturday Morning) for now. Expect the front to enter the area tonight and then stall. An associated bkn trailing line of showers/tstms also expected this eve, moving across from NW-SE and impacting southern CT and the lower Hudson Valley more than other areas. These storms will have better instability to work with, with MLCAPE closer to 1000 J/kg, so a marginal svr risk could last into the first half of tonight, with stronger cells possibly producing gusty winds and small hail. Lows tonight will be in the lower 70s near the coast, and mid/upper 60s inland. Precip with approaching low pressure should hold off until Friday night. However, there could be enough low level convergence along the old frontal boundary to spark isold-sct showers/tstms in the afternoon, particularly invof NYC metro where there the sea breeze could focus convergence further. High temps on Friday will be a seasonable lower/mid 80s.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... A shortwave across western Canada will be moving over the western ridge and into the northern plains and Great Lakes region Thursday and Friday. This shortwave will dig a trough into the eastern United States later Friday into Friday night with a surface low developing across the Ohio Valley to the mid Atlantic. The trough will dig to the Gulf of Mexico coast and into Florida by Saturday with the upper low closing off over the mid Atlantic states. This will keep a rather prolonged period of precipitation across the region. The uncertainty is how far north the upper low will be when the low closes off and also where the surface low will be. This will determine where a deformation zone sets up and where the cutoff of the precipitation will be. A cold pool will also be moving into the mid Atlantic states Friday night into Saturday increasing lapse rate with the potential for a series of thunderstorms. In addition moisture will be transported into the region from the Gulf of Mexico with precipitable water values increasing to over 2 inches late Friday night into Saturday. A low level jet will enhance lift and there will be the potential for periods of heavy rainfall from late Friday night into Saturday. The upper low lingers along the mid Atlantic coast through the weekend, however much of the energy with the low will be offshore, so precipitation is expected to wind down Sunday. Ridging builds into the area later Sunday through the middle of next week, the the Atlantic high returning by mid week. After a cool start to the week temperatures and humidity are expected to increase for the mid week period. && .AVIATION /16Z THURSDAY THROUGH MONDAY/... A weakening cold front will approach from the northwest before moving offshore late tonight. Mainly VFR through the TAF period. The exception will be at KSWF where MVFR ceilings are forecast through the day. Elsewhere, occasional MVFR ceilings are possible in and around the NYC city terminals. Showers and a few thunderstorms are likely north of the coastal terminals late this afternoon into early this evening, which could result in a brief period of MVFR conditions. Chances are lower elsewhere, so have not included any mention in the TAFs for the city terminals at this time. Light S-SW winds will return out of the south at generally 10 kt or less by mid to late morning. NY Metro Enhanced Aviation Weather Support... Detailed information, including hourly TAF wind component forecasts, can be found at: http:/ KJFK TAF Comments: MVFR ceilings possible this morning/early this afternoon. The afternoon KJFK haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KLGA TAF Comments: MVFR ceilings possible this morning/early this afternoon. The afternoon KLGA haze potential forecast is YELLOW...which implies slant range visibility 4-6SM outside of cloud. KEWR TAF Comments: MVFR ceilings possible this morning/early this afternoon. The afternoon KEWR haze potential forecast is GREEN...which implies slant range visibility 7SM or greater outside of cloud. KTEB TAF Comments: MVFR ceilings possible this morning/early this afternoon. KHPN TAF Comments: MVFR ceilings possible this morning/early this afternoon. KISP TAF Comments: No unscheduled amendments expected. .OUTLOOK FOR 12Z FRIDAY THROUGH MONDAY... .Friday...Chance of MVFR ceilings early, otherwise VFR. .Friday night-Saturday...MVFR or lower possible, with showers and possibly a tstm. NE winds G20-30kt on Saturday, mainly at the coastal terminals. .Saturday night-Monday...VFR. && .MARINE... Quiet through Friday afternoon outside of any tstms. A strengthening northeast to east flow will occur Friday night into Saturday, with wind gusts increasing to small craft levels Saturday and ocean seas building to 5 feet or greater by late Saturday. Small craft winds will continue into late Saturday night, and there is a chance that gusts could occasionally reach gale force on the ocean waters Saturday night. Small craft ocean seas are expected to remain into Monday. With high pressure across the region winds and seas will then remain below small craft advisory levels Monday night through Tuesday. && .HYDROLOGY... There is the potential for a heavy rainfall event Friday night through Saturday, especially across portions of northeastern New Jersey, New York City and Long Island. From Friday night through Saturday night rainfall is expected to range from around 1/2 to 3/4 of an inch across the Lower Hudson Valley and interior southern Connecticut to 1 1/4 to 1 1/2 inches across northeastern New Jersey and across Long Island. Local amounts of 2 to 2 1/2 inches are possible. Urban and poor drainage flooding is possible. && .OKX WATCHES/WARNINGS/ADVISORIES... CT...None. NY...None. NJ...None. MARINE...None. && $$ SYNOPSIS...Goodman/MET NEAR TERM...Tongue SHORT TERM...Goodman LONG TERM...MET AVIATION...DW MARINE...Goodman/MET HYDROLOGY...Goodman/MET is the U.S. government's official web portal to all federal, state and local government web resources and services.