Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 271420 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1020 AM EDT Sat May 27 2017 .SYNOPSIS... Weak high pressure will build over the area today and will shift offshore on Sunday...allowing us a window of dry weather. The next system over the eastern Great Lakes will lift north into Quebec Sunday night and will drag a front toward the region on Monday with rain showers. That front will slowly cross the area late Monday night and Tuesday with unsettled weather. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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10 am Update: A significant amount of clearing has occurred across the southern half of NH and extending northwest thru northern VT and will spread east the next few hours as enough subsidence under weak high pres is eroding away the low level marine layer of moisture. Made some signficant adjustments to cloud cover based on more clearing of skies than earlier expected. Due to more solar heating temps may be a bit low and may do another update to increase some max temps. No other changes attm. Update...Minor changes based on latest observational trends. Previous discussion...Trapped low level moisture and weak flow will lead to very slow clearing today. In reality it will be more like gradual lifting of the clouds with some breaks of sun. Mid level temps are still forecast to be on the chilly side...especially across the Ern half of the forecast readings in the low 60s are most likely there. Warming temps in the W at least give us an outside shot as a 70 degree reading in the CT valley.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... The stale air mass lingers over the area tonight into Sun...with little change expected. High pressure will try and nose into the forecast area from the N...but never really quite makes it to clear things out. What it will do as we head into early Sun is make an E-W pressure gradient and develop some onshore flow. Lingering low level moisture plus that light upslope flow...possibly aided by a passing s/wv trof...could lead to some patchy drizzle across Srn NH. This should dry up and lift as daytime heating commences Sun. The exception would be the NE forecast area...where stalled boundary and passing s/wv may spark some showers. More well defined s/wv ridging moving in from the W and subsidence Sun will allow for less cloud cover and warmer temps...with a good chance at some 70s inland. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... The deterministic models remain in decent agreement on the longwave pattern through late next week. We begin the period with a weak shortwave ridge cresting over the forecast area. This ridge is quickly kicked offshore by Monday morning in response to a deepening upper trough over the Great Lakes. The upper trough axis will gradually shift eastward into the northeast CONUS...where it will remain for the balance of the new work week. Temperatures this period should average below normal as troughing dominates across New England. In the dailies...a weak ridge of high pressure will retreat well offshore on Monday. Low pressure centered north of the Great Lakes will push a slow-moving occluded front across the region Monday and Tuesday with onshore flow and the advancing baroclinic zone providing a damp start to the new work week. Behind this frontal system...the unsettled weather will continue as an upper trough remains across the northeast and a series of weak cold fronts or surface troughs cross the area. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... Short Term...Areas of MVFR continue as low level moisture is very slowly eroding in the wake of low pressure. There have been some local IFR conditions at times...but I feel that today will trend towards MVFR or VFR. Especially with some afternoon heating...I think VFR CIGs will be most widespread. Tonight across Srn NH we will have to watch for a period of IFR CIGs in onshore flow and DZ. Model forecast soundings suggest a 1 to 2 kft moist layer and weak s/wv trof providing some lift. Confidence is too low to include in the TAFs for PSM and MHT at this time. Conditions will improve to VFR at all terminals Sun. Long Term... Mon - Tue...MVFR in shra with lcl IFR in fog and drizzle. Wed...areas of MVFR in -shra. && .MARINE... Short Term...Some leftover swell continues N of Port Clyde this morning. SCA for hazardous seas will continue at least into the morning before seas diminish. Otherwise weak high pressure will be in control of the waters thru the weekend...and SCA conditions are not expected. Long Term... Mon - Tue...Conditions could approach Small Craft outside the bays. && .TIDES/COASTAL FLOODING... The astronomical high tide in Portland is 11.9 feet MLLW at 119 AM Sunday. Winds are expected to be light and seas low...but high water conditions may require a coastal flood statement. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.