Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 192002 AFDGYX Area Forecast Discussion National Weather Service Gray ME 302 PM EST Mon Feb 19 2018 .SYNOPSIS...
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A warm front will enter northern New England tonight, before becoming nearly stationary along the New Hampshire and Massachusetts borders on Tuesday. The front will move north of the region Wednesday morning before a cold front sweeps through during the afternoon and early evening hours. Canadian high pressure will then follow through Thursday. A series of waves moves across the area this weekend with light rain and snow possible.
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&& .NEAR TERM /TONIGHT/...
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Initial shot of light precipitation arrives tonight in a warm air advection pattern. Atmosphere will be relatively dry at the start. This may lead to some evaporational cooling for a period over northern areas. This will likely be sufficient enough to produce some pockets of light mixed precipitation. There will be some light freezing rain and sleet into early Tuesday morning in the cooler locations. Have therefore issued a Winter Weather Advisory for the mountains of Maine for tonight into early Tuesday morning. There will be pockets of mixed precipitation in northern New Hampshire as well. However, this precipitation will mainly be confined almost exclusively to the higher terrain. Will handle this in the recreation forecast. With increasing dew points across the region as a warm front enters southern areas, expect areas of fog to develop over the colder snowpack.
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&& .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
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Any effort for the warm front to march north will be relatively futile on Tuesday as a cool drainage flow develops. Therefore, we have backed off on the high forecasts with plenty of cloud cover in the region. However, it will still be well above normal for this time of the year. Areas of fog will be slow to mix out in the morning. The exception will be the coastline where the fog may linger the entire day. Pockets of freezing rain in the north will change to rain as temperatures climb above freezing. This is similar to a typical spring onshore pattern. As is the case with these patterns, southwest New Hampshire has the chance for the warm front to be situated in the region. Therefore, there could be large temperature ranges for highs in the vicinity of areas such as Keene. Dew points increase further Tuesday night. This will allow for large areas of fog to develop with the cold snowpack still in place.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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...Wicked warm weather Wednesday... As mentioned previously, a typically spring-like weather situation is unfolding for the middle of the week. Very warm air is being vented out of the south central part of the country and through New England around a broad flat-topped ridge of high pressure in the western Atlantic. While a preceding stationary front will keep most of the area from feeling the extreme warmth on Tuesday, this will not be the case on Wednesday. As low pressure moves east into Quebec and a cold front heads east through the eastern Great Lakes and Saint Lawrence Valley, it will turn winds to the southwesterly helping to shove that front all the way north into northern Maine by Wednesday morning, putting our entire forecast area in the warm sector. While it is typical in spring for coastal Maine to stay cooler due to the cooling influences of the Gulf of Maine, this is not the case when low level wind flow is out of the west as it is projected to be on Wednesday. This will keep the sea breeze from being able to have much of an effect in southwest Maine, allowing this area to get in on the extreme warmth that southern New Hampshire will be experiencing. Being that it is February, we cannot expect the low levels to mix much further than about the 925 MB level with the westerly downsloping winds doing the heavy lifting on the mixing. Even temperatures at this level will support high temperatures in the warm areas reaching to about 70 degrees. With the westerly low level flow expected, have brought coastal New Hampshire and southwest Maine into the extreme warmth. This will meet or exceed all time February record high temperatures at our primary climate stations, likely on par with what was experienced last February 24 and 25. Note that although we do have a snow cover, this will not have much cooling effect given top down mixing of this warm air. In fact the snow cover will be a victim of this warmth. Remember the record warmth last February occurred with 12 inches of snow on the ground after all! The all time record high temperatures for the month of February are listed below, all of which are under threat of being broken Wednesday. ***Warmest February Temperatures*** Portland Concord Augusta 64 - Feb 26, 1957 69 - Feb 24, 2017 60 - Feb 18, 1981 The cold front will drop in from the northwest Wednesday afternoon and evening. Could see some showers along the front, but support for this is weakening as the front moves through the area, so the best chance for rain is in the north. Given the lack of significant rainfall in the forecast, have decided not to go with a Flood Watch, though the extreme warmth will melt a good deal of the snow pack and could lead to ice movement and jamming on area rivers. But without the rainfall, any ice jam flooding will likely be isolated. Cool high pressure moves in from the west Thursday and Thursday night. High temperatures Thursday will likely be in the morning as we are still cooling behind the front. With high pressure over the area Thursday night we could see good radiational cooling conditions, but low level dewpoints in the teens suggest that low temperatures will only fall into the teens and 20s. High pressure moves offshore on Friday with a warm southerly flow returning on the back side of it. The warm upper ridge will be backing up westward into Florida with the storm track bringing systems from west to east across New England. The first in a series of waves will be Friday night, bringing some light rain or snow on the leading edge of warm advection. The next wave moves through southern New England on Saturday, leaving southern parts of New Hampshire and Maine on the northern periphery of any precipitation associated with it. Although this positioning would favor some light snowfall, temperatures will still be quite warm even on the northern side and should result in most of this falling as rain. The last and strongest of the waves moves through on Sunday into Sunday night, tracking south of New England. This one will be strong enough to pull in enough cold air for snowfall for just about all of New Hampshire and Maine.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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Short Term...VFR conditions across the region will come to an end late this evening as increasing clouds and showers move in and a warm front enters the region. Increasing dewpoints over the snowpack will result in fog overnight dropping conditions to IFR and locally LIFR across the region. Tuesday will have a gradual improvement for all but the immediate coastline where IFR in low ceilings may remain throughout the day. Fog becomes widespread once again Tuesday night. Long Term...Should see VFR conditions on Wednesday with a cold front moving through in the evening. A series of waves moves through the region this weekend, each possibly bringing some light rain or snow and IFR conditions possible.
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&& .MARINE...
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Short Term...A south to southwest flow will continue over the region through Wednesday. SCAs have been extended for the outer waters through Tuesday with SCAs for the bays tonight. Long Term...Southwest flow ahead of the front Wednesday could reach up to about 25 KT with the flow behind the front Wednesday night also reaching up to about that range. High pressure moves through Thursday into Friday with light winds.
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&& .HYDROLOGY...
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With the warm weather expected, some melting of the snow pack is expected. This will lead to increased flows in the rivers and may lead to a few ice jams. However, with the sustained warmth and lack of significant rainfall, any ice jam flooding will likely be isolated.
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&& .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Winter Weather Advisory MEZ007>009 from 7 PM tonight to 9 AM Tuesday NH...None. MARINE...Small Craft Advisory until 6 AM EST Tuesday for ANZ151-153. Small Craft Advisory until 5 PM EST Tuesday for ANZ150-152-154.
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&& $$ Near Term...Cannon Short Term...Cannon Long Term...Kimble

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