Area Forecast Discussion
Issued by NWS Portland, ME

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334 FXUS61 KGYX 201901 AFDGYX Area Forecast Discussion National Weather Service Gray ME 301 PM EDT Sun Aug 20 2017 .SYNOPSIS... High pressure will build to the south of the region through Monday before sliding to the east on Tuesday. A cold front will move in from the west Tuesday night and cross the region on Wednesday. High pressure and drier air follows the front Wednesday night through Friday. && .NEAR TERM /UNTIL 6 AM MONDAY/...
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At 18z...a 1022 millibar high was centered over Pennsylvania. The upper trough was exiting the coast along with a few widely scattered showers. Clouds on visible imagery will begin to dissipate next few hours with loss of daytime heating. Overnight...mostly clear skies with patchy fog as high pressure builds to our south overnight. A cool and comfortable late summer night with lows in the 50s and lower 60s.
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&& .SHORT TERM /6 AM MONDAY THROUGH MONDAY NIGHT/...
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On Monday...high pressure builds by to our south with westerly flow ushering warmer and gradually more humid air into the area. Outside of a few fair weather cumulus clouds developing in daytime heating...a sunny day with highs mainly in the 80s. A few locations in southeast New Hampshire could flirt with the 90 degree mark. Partly cloudy Monday night with a few warm air advection clouds. There could be a brief shower near the international border in the predawn hours of Tuesday. Otherwise...a dry night with patchy valley fog developing overnight.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/...
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After zonal flow aloft starts off the week a deep trough will dive southwards out of the northwest territories moving into the region by Wednesday. The trough will linger over the region through the end of the week weakening as it does. Tuesday will be very warm and humid. Deep southerly flow around a Bermuda high will push warm moist air into the region. High temperatures will reach the low 90s in southern New Hampshire with dewpoints in the upper 60s, which will result in heat index approaching 95 degrees. With the strength of the high pressure have gone a bit higher on the temperatures for Tuesday. A strong cold front will approach from the west Tuesday and move through the region overnight. The front will cross western New York in the afternoon, and move through New Hampshire and western Maine overnight Tuesday into Wednesday. Due to the overnight timing, expect thunderstorms to be mainly elevated and decaying as it moves through our area, however the CT river valley could see some stronger storms as the front approaches earlier in the day. On Wednesday the front will move off into eastern Maine, with a few showers possible in the eastern portion of the area in the morning. By afternoon westerly flow will decrease humidity. Moving into the end of the week the trough will remain overhead keeping temperatures more seasonable with highs in the upper 70s south to upper 60s north and lows in the 50s. Dry conditions will continue through the start of next weekend.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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Short term /through Monday Night/...VFR...with sct MVFR and LCL IFR btw 08 - 12z Monday in valley fog. LCL IFR psb btw 08 and 12z Tue in valley fog. Long Term... Scattered thunderstorms will briefly reduce conditions to IFR overnight Tuesday into Wednesday before VFR continues through the end of the week.
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&& .MARINE...
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Short Term /through Monday Night/...Winds and seas are expected to remain below small craft as surface high pressure builds by to our south. Long Term...Southerly flow ahead of a cold front Tuesday into Tuesday night will help the outer waters reach small craft criteria.
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&& .TIDES/COASTAL FLOODING...
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We`re in the period of high astronomical tides for the month of August. The high tides of potential concern (referencing Portland Harbor where flood stage is 12.0 ft MLLW) are: 1047 PM tonight... 11.1 ft MLLW 1140 PM Monday.... 11.2 ft MLLW 1231 AM Wednesday. 11.1 ft MLLW The Tuesday night high tide (1231 AM Wednesday) could see some splashover as onshore flow and seas increase ahead of an approaching cold front.
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&& .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ SYNOPSIS...Schwibs NEAR TERM...Schwibs SHORT TERM...Schwibs LONG TERM...Curtis AVIATION...Schwibs MARINE...Curtis/Schwibs .TIDES/COASTAL FLOODING...Schwibs

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