Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 201450 AFDGYX Area Forecast Discussion National Weather Service Gray ME 950 AM EST Fri Jan 20 2017 .SYNOPSIS... Maine and New Hampshire will remain generally under the influence of high pressure...with fair weather and warmer than normal temperatures. A weak front will try and push into the area during the weekend...but is unlikely to bring us much more than very light rain or drizzle. On Sunday a cold front drops through the area...bringing more cooler temperatures than precipitation. This front will set up the battle ground between rain and mixed precipitation or snow as the next weather maker moves up the coast on Monday into Tuesday. && .NEAR TERM /TODAY/... 945AM UPDATE... Have adjusted the forecast based on current conditions. Expansive cloud cover continues to exist over most of the forecast area, though the 12Z sounding indicates this is a quite shallow cloud deck stuck directly beneath the subsidence inversion. The cloud base is high enough that it will take a little while before heating from below can generate enough mixing to dissipate this cloud cover, but continued subsidence from above could help to disperse it as well. Will hang on to it for a few more hours in the forecast before clearing things out. Have also adjusted temperature trends based on the cloud cover and latest observations. 630 AM UPDATE... Have update the grids based on current conditions and latest set of mesoscale models. Moisture remains trapped in the lower levels of the atmosphere with cloud cover over New Hampshire and communities just over the border in Maine. A second set of low cover remains over eastern areas as well, with some sunshine in between along portions of southwest Maine. Will increase cloud cover forecast based on this trend. Persistent low cloud cover, for at least a portion of this morning will likely have an effect on the max temperature forecast. Have nudged the forecast down a degree or two, but we will still be above normal for this time of the year with most areas above freezing and melting continuing. ORIGINAL DISCUSSION... Patchy morning fog will dissipate early this morning. Thereafter, a northwest flow continues aloft while a surface area of high pressure remains over the forecast area. However, some low cloudiness will continue, especially over the favorable upslope areas in the mountains as well as western portions of the forecast area. This region will be in close proximity to a low level boundary, allowing clouds to cross the region. It will remain above normal with additional melting today. Readings will be above freezing in all portions of the forecast area with above normal readings. && .SHORT TERM /TONIGHT AND SATURDAY/... A weak upper level disturbance will bring more clouds to the region tonight as it rotates and shears out into upper level ridge. Weak dynamics and modest moisture supply aloft should prevent precipitation during the overnight hours. However increasing moisture in the lower levels could set the stage for patchy drizzle/freezing drizzle or a few flurries. Confidence level remains low in this low pop forecast. On Saturday, spotty very light precipitation is expected despite the weak dynamics involved with this system. There could be patchy drizzle and a pocket or two of very light mixed precipitation as well. The focus of any precip would mainly occur over New Hampshire and the adjacent areas of western Maine. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... An exiting short wave in the maritimes allows a large surface Canadian ridge of high pressure to build into northern New England Sunday supplying a shot of cold air into the lower and mid levels. In the mean time, the upper low tracking along the southern states over the weekend gets ejected to the northeast and redevelops off the mid Atlantic coast near DELMARVA and then tracks northeast hugging the New England coast and moving along the Maine coast by Tuesday. Strong UVV will accompany the upper system as it becomes negatively tilted. Considering its source region in the deep south, this system will have plenty of moisture that will override the initial cold dome in place so the ptype will start as snow across all areas. It gets complicated as to how much warm air will work inland on the strong low level southeast jet. Substantial snows could occur in the mountains and foothills before any changeover while along the coast and adjacent inland areas some light amounts of snow may occur before changing to a mixed bag and then even some rain along the coast. QPF totals will range from 1-2 inches over much of the area with highest amounts along the coast. Snow accumulations ratios were based on temperatures ranging from 8:1 along the coast to 13:1 in the mountains. The system exits into the maritimes by Wed with some clearing although a dirty ridge will remain. A broad upper trof with an associated cold front will bring a return to colder air and scattered snow showers late in the week mainly to the mountains. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... Short Term...MVFR conditions will continue over the western portion of the forecast area with some low ceilings today. There will also be patchy fog lowering visibilities through early this morning. Otherwise generally VFR into tonight. A weak upper level disturbance and low level boundary will remain over western areas Saturday before shifting east. This will bring more MVFR conditions with possible localized IFR conditions in patchy drizzle and/or freezing drizzle. Long Term...Conditions will lower to IFR/LIFR late Monday through Tuesday in a mixed precipitation due to the coastal low affecting the area late Monday into Tuesday. Conditions return to VFR by Wednesday. && .MARINE... Short Term...Long period swells continue to reach the coast. The SCAs for seas may need to be extended for a couple more hours this morning. Will continue to monitor, however have raised the seas forecast over guidance for this morning. More dramatic increase in the seas will be noted for the extended portion of the forecast. Long Term...A coastal low will develop off the mid Atlantic coast late Sunday into Monday and then move north into the Gulf of Maine with Gale force winds that may approach Storm force gusts for a time Monday night into Tuesday. Seas will build to 15-20 feet over the outer waters. The system exits northeast into the maritimes Tuesday night and Wednesday with backing diminishing winds allowing seas to be knocked down. && .TIDES/COASTAL FLOODING... Despite being at the low part of our tide cycle, large building waves may product some splash-over near the time of high tide Monday night and Tuesday. Preliminary storm surge values appear to be around 1.5-2.0 feet with a persistent easterly gale developing. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ NEAR TERM...Kimble SHORT TERM...Cannon LONG TERM...Marine is the U.S. government's official web portal to all federal, state and local government web resources and services.