Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 081701 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1201 PM EST Fri Dec 8 2017 .SYNOPSIS... High pressure will continue to slowly build into the region today with fair weather expected for most of the area. A pattern change begins to take hold this a coastal low will develop offshore Saturday. This looks like it will deliver snow to much of the forecast area Saturday into Saturday night. Beyond the weekend we will have to watch for another coastal low developing offshore...especially midweek...that could deliver some snow to the region but confidence is currently low. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1155 AM...Minor ESTF update to ingest the current mesonet and satellite trends into near term grids. Prev disc... 900 AM...We continue to see a few mountain flurries with the lake effect moisture to the lee of Lake Ontario. Otherwise...a dry and seasonable day under weak ridging. For this ESTF update...minor adjustments were made to near term grids that reflect light snow showers across the higher terrain...satellite low cloud trends...and the current mesonet. Winds and seas continue to diminish and I anticipate allowing the current small craft to expire on time at 16z. Prev disc... We still have some snow showers across the mountain zones early this morning aided by moisture emanating from the Great Lakes. These will wane this morning as weak high pressure builds into New England. Otherwise, partly to mostly sunny skies are expected today with highs mainly in the 30s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... Our first significant snow event of the season appears to be on the doorstep as low pressure forms offshore Saturday. The snowflakes will hold off tonight as forcing for ascent remains to our south. On Saturday, increasing forcing for ascent and moisture will allow light snow to overspread the region from south to north during the day. At this time, the 00z deterministic models and latest ensemble members are in good agreement with a general 3-6" snow event. The best forcing for ascent and snow growth looks to remain offshore this go around which should preclude a warning event (6"+) for the vast majority of the area. Will allow the dayshift to review 12z guidance before hoisting any headlines at this time as there is some wiggle room here for east or west trends. The heaviest snow is expected to occur Saturday afternoon and evening before tapering off and ending later Saturday night and early Sunday morning. && .LONG TERM /SUNDAY THROUGH THURSDAY/... A well advertised pattern shift arrives starting this weekend as a long wave trough sets up over the eastern portion of the United states. This will allow a series of storms to move through our area. Sunday will see our departing storm moving east leaving the area under northwesterly flow and cold advection. Scattered snow showers will continue throughout the area with froude numbers indicating the showers may propagate away from the mountain crests through the middle of the day. Showers should come to an end overnight but expect some moisture to remain and keep temperatures up slightly. Monday a weak short wave moves through to our north and may touch off another round of snow showers in the mountains. This shortwave will also serve to drive the trough further east pushing the core of the cold air over our region for Monday night. With at least weak high pressure in place for Monday night have forecasted on the colder end of the guidance with the mountain valley dropping into the low single digits. All of the snow showers early in the week are really just a preamble for a mid week storm. As the 500mb trough axis moves into western New York, the storm track begins to move around the base of the trough and up the east coast setting up northern New England for precipitation through midweek. The vast majority of deterministic and ensemble runs have a low passing near us from Tuesday night into Wednesday and thus have fairly high confidence that precipitation will occur. As is often the case with these systems the devil is in the details and the low track options, which currently range from the St. Lawrence to east of the 70/40 benchmark provide an equally diverse range of solutions. The more inland low track, favored by the recent GFS would put us on the warm side of things... at least aloft. With the departing cold high pressure that could set us up for a mixed precipitation or freezing rain event. However the operational euro and a majority of ensemble members would put the storm up the coastline which leaves us in a more standard nor`easter mainly snow track. At this point the driving force behind the development of this system is still not even onshore in British Columbia so will remain conservative for this forecast package. Overall, I would tend to favor the more classic coastal low option as the ocean temperature gradients can really help to strengthen storms this time of year and so have left the forecast ptype as all snow/rain in deference to the coastward track solution. Wind speeds over the ocean have also been increased somewhat as any intensifying coastal low would result in gale force over the waters. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... Short Term...VFR conditions are expected today except for some occasional MVFR in the mountains. Otherwise, VFR tonight through Saturday morning before snow arrives Saturday afternoon and drops conditions to IFR Saturday night. Long Term... A mixture of VFR and MVFR SHSN will continue through the day on Sunday and even into early Monday morning. High pressure makes a brief return to VFR before the next low approaches on Tuesday. Expect IFR with snow across most of the area for Tuesday night into Wednesday. && .MARINE... Short Term...SCA conditions for the ocean waters continues into this morning before relaxing. SCA conditions are once again likely Saturday night as low pressure moves just east of the Gulf of Maine. Long Term... Northwesterly cold advection will keep SCA conditions in the waters through the day on Sunday before seas and winds subside Sunday night. Calm conditions hold through the start of the week before the next low approaches for Tuesday. This storm may bring Gales to the waters. && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...None. NH...None. MARINE...None.
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