Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 130240 AFDGYX Area Forecast Discussion National Weather Service Gray ME 940 PM EST Sun Nov 12 2017 .SYNOPSIS... High pressure will shift east tonight as weak low pressure moves east out of the Ohio Valley. Weak low pressure will pass south of New England on Monday. High pressure will gradually build in from the northwest Monday night through Tuesday and will hold over the region Wednesday. A cold front will approach from the west Wednesday night and will cross the region on Thursday. High pressure will build in from the west Thursday night and Friday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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935 pm Update: Skies have become clear across all areas and winds are calm. Temps falling due to radiational cooling as forecast. Made some adjustments to sky grids based on current trend of short wave ridging over the area allowing subsidence to allow clear skies well into the night. Late tonight still expecting mid/high clouds to spread into the region from the approaching system to the west. 640 pm Update: Temps falling a little slower than forecast so minor tweaks to temps for the evening. Also, cloud cover widespread across the mountains and foothills of ME/NH so put in cloud cover for those areas through the evening. Previous Discussion: High pressure will drift east into the maritimes tonight as weak low pressure moves east out of the Ohio valley. Mid level clouds over northern and eastern zones will gradually diminish through early evening before more mid level clouds move into southern zones after midnight. Lows overnight will range through the teens in the north and lower to mid 20s south.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Low pressure will pass out to sea south of New England on Monday resulting in variable clouds through the day. Associated precipitation will generally remain south of the region but have gone with lower chance pops seen in the new GFS for southern zones. Expect any precip to be in the form of a mix of rain...snow or sleet in the morning...going over to rain showers in the afternoon. With very dry air mass in place... expect this activity to be light and spotty with little impact. High temperatures will range from the mid 30s to near 40. Low pressure heads out to sea Monday night leaving a fair amount of low level moisture lingering over the forecast area. Lows overnight will generally range through the 20s. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Surface ridging will dominate wx to start the extended. A weak upper trof passing overhead however may keep enough high and mid level moisture to prevent us from completely clearing out. If we clear out...temps will probably go below guidance...so I hedged in this direction but not below MOS guidance. Wed a stronger upper trof will approach from the Great Lakes driving a cold front towards the area. Some differences between guidance is already developing at this range though...with the 12.12z GFS shearing the s/wv out and weakening the surface front. The 12.12z CMC and ECMWF however amplify the trof as it approaches...and so bring stronger forcing for ascent and more precip to the area. This has implications for the area...as temps will initially be cold enough for precip to fall as snow across much of the area. The more strongly forced scenarios would have the potential for accumulations across the foothills and mtns...but will also warm the near coast faster and more likely lead to rain there. Some lingering upslope precip will continue in the mtns into Thu night. The strongest trof of the series will arrive over the weekend. Low pressure will develop and move NEwd thru the Great Lakes towards Canada. The downstream pattern is one that could be favorable for blocking and thus some trends towards cooler solutions with time. As it is both the 12.12z GEFS and ECMWF EPS have a very baggy look to the mean SLP...suggesting low redevelopment or triple point formation near the coast. A fair number of individual ensemble members develop low pressure centers near the coast and weaken the primary lows across Ontario. Given this trend I have blended in some cooler raw model 2 m temps Sat where cold air damming is a possibility. This could also bring more wintry precip into play...but considering this is day 7 and beyond I have not added any more ptypes beyond rain and snow. && .AVIATION /03Z MONDAY THROUGH FRIDAY/... Short Term...VFR tonight. Areas of MVFR/IFR ceilings developing Monday afternoon and persisting through Monday night. Long Term...Surface ridging will bring widespread VFR conditions thru Wed. Wed night into Thu a cold front approaching form the W will spread SHRA/SHSN across the region. Temps will initially be cold enough for SHSN across the interior...which could bring local IFR conditions to interior terminals. Behind the front MVFR to occasional IFR conditions will linger at HIE in upslope flow. && .MARINE... Short Term...No flags. Long Term...Developing NE flow over the coastal waters may bring seas up to near 5 ft by midweek outside of the bays. More likely offshore winds behind a cold front Thu...winds and seas will increase to SCA thresholds thru end the week. A stronger low pressure system over the weekend will bring increasing Sly flow ahead of it...with higher winds and building seas. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Marine

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