Area Forecast Discussion
Issued by NWS Portland, ME

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220 FXUS61 KGYX 250710 AFDGYX Area Forecast Discussion National Weather Service Gray ME 310 AM EDT Tue Apr 25 2017 .SYNOPSIS...
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An onshore flow will transport cool, moist air off the Gulf of Maine today into Thursday. Today drizzle and rain will begin to overspread the region with rain becoming heavier tonight into Wednesday as low pressure moves north along the East Coast. The cool, moist maritime air may linger into Thursday east of the mountains, but warm air will begin to move into western New England and eventually even make it to the Maine coast this weekend.
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&& .NEAR TERM /THROUGH TODAY/...
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Areas of maritime drizzle and fog will remain off the coast early this morning, before coming onshore today. Meanwhile, rain will continue to spread northward from southern New England today as a surface area of low pressure reaches the Mid Atlantic coastline. With easterly winds developing, temperatures will be much cooler along the coastline, with only 40s for highs in most areas.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM WEDNESDAY/...
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Rain will continue tonight with widespread drizzle and fog as a deep maritime influence will overspread much of the region. Low pressure will slowly fill as it moves up the New Jersey coastline. Nevertheless, trajectories over the open Atlantic and slow movement of the sysetm will increase the rainfall totals over the region despite not an overly impressive dynamic pattern. By Wednesday, the upper level low pressure system begins to open with time as a surface low dissipate as it approaches Nantucket Island. The heaviest rain will fall in the morning, before the precipitation begins to lighten with time. Temperatures will struggle to climb through the 50s in most sections with a southeast flow continuing over the region, albiet light. Some warmer temperatures may occur in the downslope regions of the Connecticut River Valley. QPF: Rainfall totals over 1 to 2 inches are still expected over southern areas, mainly in and around the coastline. There may be a few local spots that exceed 2 inches of rain in any persistent periods of heavy rain.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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Low pressure drifts northeast into the Gulf of Maine Wednesday night and Thursday. This will continue a persistent onshore flow keeping low levels saturated. The stratiform rain, drizzle and areas of fog will continue Wednesday night and by Thursday only the drizzle and areas of morning fog should remain. Models indicate by Thursday night the low moves far enough offshore to allow some clearing in the mid/high levels but lack of any ventilation of drier air in the lower levels should keep low levels moist with stratus remaining, especially southern and eastern areas. Temps warm aloft Friday but unfortunately the combo of the clouds and a developing south flow will keep temps from reaching their potential, although southern areas of NH may reach into the 70s. A weak short wave moves through late Friday so scattered showers and even the chance of afternoon thunderstorms may occur. Over the weekend a large broad Bermuda high sets up off the east coast with its northern periphery of a warm southwest flow aloft reaching into northern New England. Models are having a tough time trying to resolve any short waves traveling around the outer periphery of the large high into New England. This will make or break the weekend with either a mild nice weekend versus a wet damp weekend. Confidence at this time is low on the outcome.
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&& .AVIATION /07Z TUESDAY THROUGH SATURDAY/...
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Short Term...VFR conditions this evening will begin to transition to MVFR and then IFR conditions from south to north during the day Tuesday as low level moisture spills in off the Gulf of Maine. There could be an area of lower clouds arriving along the immediate coast as early as tonight which would bring a threat for LIFR conditions. But the broader forecast is for worsening conditions on Tuesday with just about all areas IFR or worse by Tuesday evening in drizzle and light rain which will likely last through Wednesday. To the northwest of the mountains up in Whitefield, conditions may stay VFR to MVFR until the better forcing for rain arrives Tuesday night. Long Term...Lingering IFR/LIFR conditions likely through Thursday. Improvement to VFR/MVFR likely for Thursday night into Friday...with occasional restrictions in SHRA and possible TSRA possible Friday afternoon. Frontal boundary remains across the region through the weekend with VFR likely dominating...but scattered MVFR/IFR restrictions in SHRA possible.
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&& .MARINE...
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Short Term...Expect an increasing easterly flow tonight into Tuesday, with winds as high as 25 KT beginning Tuesday afternoon. Winds shift to the southeast on Wednesday and decrease in intensity Wednesday night. The onshore fetch will allow wave heights to build up to 5 to 9 FT through Wednesday night. Long Term...While winds will subside...lingering deep water swells will likley necessitate SCAs over the outer waters into the weekend.
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&& .FIRE WEATHER...
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Moist onshore flow will bring high humidity and a wetting rain to all areas today through at least Wednesday.
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&& .HYDROLOGY...
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Continued snow melt in the mountains will keep river levels high. Rain expected this afternoon and Wednesday will add runoff to area rivers already at high levels. While widespread flooding is not expected, it is not out of the question that a few rivers could reach minor flood stage.
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&& .TIDES/COASTAL FLOODING...
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High astronomical tides begin tonight and last through the weekend. The combination of high tides and an onshore flow with the coastal low will bring the chance of beach erosion, splash over, and minor coastal flooding during the time of high tide tonight and again Wednesday night. There is relatively good agreement between the WRMGYX forecasts and in-house matrices for this event. Minor expects will be possible, from Portland Harbor and points south.
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&& .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory from 7 PM this evening to 6 PM EDT Wednesday for ANZ151-153. Small Craft Advisory from 2 PM this afternoon to 6 PM EDT Wednesday for ANZ150-152-154. && $$ NEAR TERM...Cannon SHORT TERM...Cannon LONG TERM...Marine

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