Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 280225 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1025 PM EDT Tue Oct 27 2020 .SYNOPSIS... Cool high pressure builds into the area this evening before moving offshore overnight. A weak disturbance may bring a few showers to the area tomorrow. Towards the end of the work week, low pressure tracks eastward to the south of New England just as an Arctic cold front brings much colder air into the area from the north. Rain is likely to begin in southern areas on Thursday with rain changing to snow on Friday as the temperature cools. This will be the first accumulating snow of the season for many areas. Cold weather lasts through at least Saturday before high pressure shifts east and allows temperatures to slowly rebound. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Update... Have issued an update as scattered rain and snow showers continue to head southeast across southernmost portions of our forecast area this evening. Latest mesoscale models show a second batch of very light precipitation crossing southern portions of the forecast area tonight into Wednesday morning. Have modified pops across southern areas, however they still remain relatively low, in the chance or slight chance category. Some of the precipitation continues to fall into dry lower levels and is evaporating before it reaches the ground. This dry layer is depicted well by the 00Z GYX sounding which depicts an unsaturated layer below 6500 feet. Made minor adjustments to temperatures, dew points and winds in the near and short term portion of the forecast. Otherwise, this weak impulse will mostly bring clouds to the region, mainly to southern areas. Prev Disc... Satellite imagery shows clearing across much of the area associated with a cooler, drier air mass filtering in from the north behind a departing boundary. Downsloping, gusty NW winds have allowed stratus to clear out except for over the mountains. Where we still have stratus there may be a few flurries. Sunny skies over the coastal plain have helped temperatures reach near of above 50 degrees. Across the higher terrain we remain in the upper 30s to 40s. Tonight skies become cloudy once again with a disturbance moving towards southern New England. This may result in a few showers across southern NH towards morning. Temperatures will be cold with most areas seeing a hard freeze towards morning. We will see chillier readings where skies are clear the longest, with lower 20s across the north. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Low pressure deepens as it moves over Long Island and well south of the Gulf of Maine during the afternoon hours Wednesday. This may continue to brush southern sections with rain showers through early afternoon before pushing east. Temperatures will be just below normal with lower to mid 40s across much of the area. Low to mid 50s will be possible along the coast and southern NH. WNW winds return Wednesday night and overnight lows will not be quite as cool as tonight. We will see a familiar pattern with skies clearing out later in the day before increasing after dark ahead of the next surge of theta-e from the south. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Impacts: Low pressure passing south of the area will bring rain, changing to snow across the region Thursday night into Friday. Forecast Evolution: There are two features we are tracking for Thursdays storm. First of all, Hurricane Zeta, which is currently moving north through the Gulf of Mexico will move into the Mississippi river delta region on Wednesday night and undergo extra tropical transition as it moves inland. Aiding in that transition will be an upper level low over the southwest and surface cold front which has produced freezing rain over Oklahoma. As both of these features move up the Ohio river valley on Thursday they will interact. The result is a system that upon exiting the east coast over NJ Thursday night will contain tropical moisture, upper level support, and cold air. These are all the ingredients necessary for a widespread early season snowfall, how they combine still leaves plenty of variability. The operational deterministic models have been bouncing around quite a bit, however the ensemble mean shows a more consistent measured view. In this view the trend is for the low pressure to be more elongated as the remains of Zeta outrun the upper level trough. The result for New England is a decrease in both QPF and snowfall as the best forcing for ascent passes to our south. Expect a sharp gradient on the northern edge of the system, with this gradient likely falling in the southern 1/2 of our CWA. With this in mind have tried to tighten up the PoPs, keeping the far north dry, while going to likely PoP on the Mass border. For temperatures, it`s a complex system. With the NEly flow we typically see some cold air damming and have kept the temps slightly lower through the morning hours on Friday in deference to this however for the cold air to dam it has to be there in the first place and with the source of the cold to the NW behind the secondary system, our NEly surface flow wont do as much to drop temps. Further the ocean water remains relatively warm, thus expect coastward of Rt 1 to remain in rain. The overlap between the QPF and cold air is in the NW quadrant of the storm, which falls in SW NH. This is where, especially at the higher elevations of the monadnocks, we could see snowfall amount over the current forecast as strong upward motion will be present if the temperatures remain cold enough. Snowfall amounts are still uncertain but what is becoming higher confidence is for an accumulating snowfall event across southern NH. With this being the first snow of the season for many expect impacts to be higher than midwinter as trees with leaves, and a low level jet allowing for winds of 20-30mph across the region overnight. The storm will clear out Friday night, with cold high pressure building in for the weekend. With all the focus on the snowfall, have stuck with a consensus of the models for the weekend temps as this was a higher confidence and lower impact time period. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... Short Term...Mostly VFR through tonight, with some lingering MVFR ceilings for KHIE. Lowering conditions to MVFR or perhaps lower towards early morning for southern NH TAF sites, spreading east towards coastal terminals by morning. We may see -DZ, -RA, and fog at times before conditions improve after 18Z Wed, with occasional -SHSN possible at KHIE. Long Term...Low pressure passing south of the region will push rain into the region late Thursday resulting in IFR conditions across the southern half of the CWA. Rain will change to snow overnight as cold air moves into the region with IFR continuing through Friday morning. Skies will clear Friday afternoon for the coast with MVFR lingering the mountains overnight. VFR on the weekend as high pressure builds into the region. && .MARINE... Short Term...Northwest winds will continue to gust to 20 knots this afternoon over the outer waters in a relatively well mixed environment before diminishing tonight. Winds and waves may touch SCA conditions late tonight/early tomorrow morning with low pressure in the area, mainly for the eastern outer waters. However, this will be very limited so a SCA was not issued. Long Term... NEly flow ahead of a system passing near the benchmark Friday night will bring winds and seas to near SCA on the outer waters. Behind the system on Friday night increasing Cold air advection and NWly flow will result in SCA hold through through the start of the weekend. High pressure will build in for the weekend. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ JC/WW/MC

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