Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 221155 AFDGYX Area Forecast Discussion National Weather Service Gray ME 655 AM EST Mon Jan 22 2018 .SYNOPSIS... A cold front will drop south through northern New England today with colder temperatures returning. Some light snow is expected as well, with the front lifting back north as a warm front tonight and Tuesday. As it does so, expect a period of freezing rain for most areas before temperatures warm. As the low moves away Tuesday evening a cold front will move across the area from west to east with colder temperatures expected Wednesday through Friday. && .NEAR TERM /TODAY/...
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7AM UPDATE... Colder air is moving in from the northeast this morning with some light snow falling behind it. Some light drizzle or freezing drizzle has been observed in far southern New Hampshire and southwest Maine. As cold air continues to move in, expect precipitation type to favor snow as the day goes on, with some light accumulations possible. ORIGINAL DISCUSSION... A cold front is moving south through the area this morning with some light snow falling along and just behind this front across northern New Hampshire and central Maine. Further south, some light warm advection precipitation has moved into southern New England. Expect the cold front to continue moving south and into southern New England today with temperatures falling behind it. There exists a pretty strong temperature gradient across this boundary in northern Maine and Quebec, and some models even show temperatures falling into the teens this afternoon across much of western Maine. Have taken this into account with the temperature forecast today, but did not go quite that extreme. Meanwhile, light warm advection snowfall should continue on and off across the area today with intensity picking up just a bit this afternoon. An inch, maybe two inches, of snow is possible with this.
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&& .SHORT TERM /TONIGHT THROUGH TUESDAY NIGHT/... More organized area of warm advection snowfall expected to move north through the area tonight as the front tries to lift back north as a warm front. Cold air damming will hold in tough at the surface, so the surface front should get hung up near the New Hampshire/Massachusetts border while the front aloft lifts northward. The majority of the precipitation should fall north of this aloft front primarily in the form of snow, with temperatures aloft warming behind the front as the steadier precipitation briefly ends. Could see some light freezing drizzle or freezing rain within the cold air dammed area by morning once the snow has ended. Primary area of low pressure is moving through the Saint Lawrence Valley on Tuesday, but expect secondary low pressure to form along the stalled surface warm front and move east during the day spreading another round of steadier precipitation across the area. While some additional snow is possible in the northern parts of the forecast area, most of the area will see this fall as freezing rain or rain depending on ground level temperatures. Models continue to struggle a bit with this cold air damming, but some of the higher resolution models are more successful in showing this. Confidence is high that the cold air damming will occur as the low level easterly flow north of the warm front will keep the cold air shoved in place east of the mountains. There is some doubt as to what the temperature will be within the dammed area, but observed dewpoints within the cold air mass over northern Maine and southern Quebec this morning are near zero, so there should be enough cold/dry air to support temperatures below freezing as the heavier precipitation arrives Tuesday morning. However, as the rain freezes it releases heat and will allow low level temperatures to warm fairly quickly up to around the freezing mark within the dammed area. Meanwhile, the surface warm front will lift north into southern New Hampshire fairly early in the morning and push onshore of the Maine coastline as well with temperatures in the 40s and 50s behind it. To the west of the mountains, downsloping should allow the temperature to warm above freezing. It is the area from Conway to Skowhegan that will have the greatest threat of freezing rain, though we do expect the ice to have difficulty sticking to roads and trees after the overnight snowfall, instead forming a crust on top of the snow and icing any cleared areas. Winter Weather Advisories have been issued for the entire forecast area, with the timing extending until noon for western, central, and southern New Hampshire as well as the Maine coastline as temperatures are expected to warm above freezing by then. Further inland the advisories continue until 6 PM as the cold air damming will keep the threat for freezing rain in these areas longer. Further north there will be greater snowfall totals including the possibility of more than 6 inches total, however confidence is low on seeing widespread 6+ inches and thus a Warning has not been issued. As low pressure moves east across the area it will pull a cold front across along with it. While temperatures behind the front do fall, the areas that were dammed ahead of the front will actually see the temperature warm a bit behind the front before cooling later in the night. The majority of the precipitation will fall along and ahead of the front while some lingering showers (becoming snow showers) are possible behind the departing low Tuesday night. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Models all agree on Arctic high pressure building southeast across the region Wed through Fri and becoming centered over New England by Fri night. Northwest winds will be gusty Wed and Thu but diminish on Fri. A return to much colder temps will occur for this time period. In the mountains widely scattered snow showers are possible while elsewhere dry conditions are expected. On Saturday, in response to a digging long wave trof over the upper midwest, the Arctic ridge of high pressure moves well off the coast allowing a warmer southwest flow to develop at the surface as well as aloft. Mixed precipitation will move into the region Sat night and into Sun as the base of the upper trof progresses east. A cold front will arrive sometime Sunday. Generally accepted the superblend temps/POPs for the outlook period. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... Short Term... Expect ceilings to lower as the day goes on with some light snow possible at all airports. Conditions gradually become IFR by tonight as precipitation becomes heavier and ceilings lower. Expect a period of freezing rain especially east of the mountains early on Tuesday, with temperatures warming above freezing in southern New Hampshire and coastal Maine during the morning. A cold front crosses the area Tuesday evening and should help end the prolonged IFR conditions with the exceptions of the areas north of the mountains. Long Term...VFR conditions Wed through Fri except briefly MVFR conditions in the mountains in any snow showers. && .MARINE... Short Term...A cold front drops south across the waters tonight with a northeast wind developing behind it. This front lifts back north as a warm front tonight into Tuesday with low pressure moving east along it. Expect a southerly gale on Tuesday as the low pressure moves along the front and drags a cold front eastward along with it. Long Term...SCA conditions are expected Wed through Fri due to a strong northwest flow as Arctic high pressure builds Southeast across the waters. && .HYDROLOGY... A Flood Watch is in effect for the southern half of New Hampshire as well as the coastal plain of Maine. These areas are expected to get significant liquid precipitation during the day on Tuesday which may cause ice movement and possible ice jams on area rivers. This could lead to minor flooding especially near areas affected by ice jams. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...Flood Watch from Tuesday morning through late Tuesday night for MEZ012-018>028. Winter Weather Advisory from 4 PM this afternoon to 6 PM EST Tuesday for MEZ007>009-012>014-018>022. Winter Weather Advisory from 4 PM this afternoon to noon EST Tuesday for MEZ023>028. NH...Flood Watch from Tuesday morning through late Tuesday night for NHZ003>015. Winter Weather Advisory from 4 PM this afternoon to 6 PM EST Tuesday for NHZ001-002-004-006. Winter Weather Advisory from 4 PM this afternoon to noon EST Tuesday for NHZ003-005-007>015. MARINE...Small Craft Advisory from noon to 11 PM EST Tuesday for ANZ153. Gale Warning from noon to 11 PM EST Tuesday for ANZ150>152-154. && $$ NEAR TERM...Kimble SHORT TERM...Kimble LONG TERM...Marine is the U.S. government's official web portal to all federal, state and local government web resources and services.