Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 182241 AAA AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 541 PM EST Sun Feb 18 2018 .SYNOPSIS... High pressure will build across the region through tonight before moving east of northern New England Monday. A warm front will move north of the region Tuesday and usher in very warm air for this time of year. A cold front will move through Thursday ushering in some cooler air for the end of the week. Another two areas of low pressure will move northeast from the Ohio River Valley next weekend. These systems will bring more unsettled weather and possibly mixed precipitation to portions of Maine and New Hampshire. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Update...Minor changes to reflect latest observational trends. Some snow showers are visible on radar and confirmed by automated observing stations in Nrn NH and Wrn ME mtns. I do not expect significant accumulation...but did add some isolated to scattered snow shower wording in upslope zones for the next couple of hours until flow becomes more SWly. Previous discussion...At 19z...a 1033 millibar high was centered across the DELMARVA while a 985 millibar low was centered southeast of Nova Scotia. GOES visible imagery showed some lingering upslope clouds across mainly the high terrain with a few cloud streets extending onto the coastal plain. There were also a few flurries lingering across areas near the international border. Temperatures were mainly in the 30s with a few 40 degree readings over southeast New Hampshire and along the southwest Maine coast. For tonight...winds diminish this evening as the gradient relaxes across the forecast area. Some warm air advection clouds will spread into northern sections overnight. Otherwise...a mainly clear night across the area. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... On Monday...return flow behind the departing surface high will warm temperatures into the 40s with a few upper 30s along the international border. The initial band of warm air advection clouds will lift to the north of the area with sunshine giving way to a second band of warm air advection clouds during the afternoon. We`ll see some rain showers break out by late in the day...although near the international border we may see enough cold air in the column for some patchy snow, sleet, and freezing rain. The warm air advection precipitation will become more widespread Monday night with activity tapering to drizzle over southern sections overnight. There may be some pockets of residual cold air along the international border in Maine for some patchy snow, sleet, or freezing rain otherwise precipitation will be rain. The warmer air over the snowpack should result in widespread fog and some drizzle especially in areas south and east of the mountains. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Wild swings in temperatures possible this week. Uncertainty continues with forecast temperatures during the midweek period. All models within the 12Z model suite remain in good overall agreement as to the large scale synoptic patterns. A large upper level ridge will develop along the eastern United States beginning Monday. Cold, dry air will initially be in place as a broad area of overunning associated with warm air advection begins. This will allow for the atmosphere to gradually saturday, bringing light precipitation to the region by Monday afternoon or evening. Northern portions of New Hampshire and the western mountains of Maine may see mixed precipitation with this initial shot of moisture. The forecast becomes somewhat more complicated for Tuesday. Initially, there will likely be plenty of low level moisture in terms of increasing surface dew points and melting of the snowpack. Thereafter, there are mixed signals as to the strengthen of the westerly flow aloft allowing warm air to dynamically work its way to the surface. However, there are other models that indicate a northerly drainage flow may develop, creating an inversion over the region. An inversion and low level drainage flow from the north would mean a cooler forecast on Tuesday for central, northern and perhaps coastal portions of the forecast area. So with conflicting signals, may need to play a blend in the forecast high temperatures for this time period. There still remains the potential for very mild temperatures to develop south of the warm front over southernmost New Hampshire. All in all, much uncertainty exists on Tuesday. There will be showers Tuesday and Tuesday night along and ahead of a frontal system to our north. However, most of the precipitation will be over northernmost portions of the forecast area. Area of dense fog with dew points well into the 40s will likely start the day on Wednesday. Morning temperatures may be warm enough to set minimax readings by the end of the day. Snow pack will continue to erode during the day to some extent. A strong low level westerly flow will continue, but this time with cold air advection developing during the afternoon hours. This weak cold air advection well ahead of the main surface cold front may be sufficient to increase mixing in the lower layers of the atmosphere and allow for partial clearing downwind of the mountains. With H8 temperatures still at or above +10C, very mild readings can be expected. The record highs on Wednesday may be in jeopardy of falling in many areas. In terms of records, here they are below for Portland and Concord with the Tuesday record highs potentially much tougher to reach. ***Records for PWM & CON*** TUE WED PWM 61/1994 59/1953 CON 66/1930 64/1872 Note: Record warm overnight lows range from the upper 30s to lower 40s during this period for portions of the region. Despite cold air advection continuing on Thursday, there is not an overly abundant area of cold air behind this system. Still expected temperatures above normal for this time of the year. Quiet conditions will follow with Canadian high pressure for the rest of the end of the work week. However, thereafter, two complex systems will head north from the Ohio River Valley next weekend. These systems may bring a mix to the region. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... Short Term /through Monday Night/...VFR. Gusty NW wind up to 25 kt diminishing aft 22z today. Aft 20z Monday...MVFR developing in -shra with widespread IFR aft 02z Tue in -ra and fog with pockets of -sn,-pl, -fzra psb in the mountains. Long Term...Expect variable conditions on Tuesday to deteriorate to IFR with locally LIFR conditions Tuesday night in fog and periods of light rain. The precipitation will mainly be confined to northern areas. MVFR ceilings possible Wednesday, however ceilings and visibilities will be dropping with the approach of a cold front late in the day and during the evening hours. VFR conditions thereafter with high pressure through the end of the work week. && .MARINE... Short Term /through Monday Night/...SCA remains in effect for all waters except Casco Bay through early evening in the wake of departing low pressure. Winds and seas continue to diminish overnight as high pressure builds in from the SW. Return flow over the waters is forecast to increase quickly tomorrow...with marginal small craft conditions possible outside the bays late tomorrow into tomorrow night. Long Term...Expect SCA will be needed late Monday. Gusty winds may continue Tuesday and Wednesday because of an increasing southwest gradient with building seas. && .HYDROLOGY... We will have to monitor the rivers closely next week as the warm weather and some rain may lead to enough runoff to cause ice jam flooding. There are several locations with ice jams in Maine and New Hampshire. Looks like a 72 hour period or longer with temperatures remaining above freezing. It is possible that the warmer weather will weaken the ice so that any rise in river levels will just move the ice harmlessly downriver. QPF should be fairly light with less than a quarter inch expected Monday night through Wednesday in the south and up to an inch in the far north. .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory from 10 AM Monday to 5 AM EST Tuesday for ANZ150-152-154. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory from 10 AM Monday to 5 AM EST Tuesday for ANZ150-152-154. && $$ NEAR TERM...Legro

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