Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 160843 AFDGYX Area Forecast Discussion National Weather Service Gray ME 343 AM EST Fri Feb 16 2018 .SYNOPSIS... A weak wave of low pressure will move east of the region this morning...taking early morning shower activity with it. A secondary front will arrive later today bringing with it a few rain and snow showers...with much colder and drier air filtering into the region for tonight and Saturday. Low pressure will move south and east of New England Saturday night and Sunday bringing the potential for an accumulating snowfall...particularly to southern New Hampshire and the coast of Maine. As we move into next week...a warming trend is expected with temperatures moving well above seasonal norms...especially by Tuesday and Wednesday. There will be multiple chances for rain showers through next week. && .NEAR TERM /Today/... High Impact Weather Potential: * Locally dense fog coming to an end through daybreak. Pattern: Surface map early this morning reveals weak wave of low pressure along WSW-ENE draped boundary arriving over southern New England...with a region of rain showers making a glancing blow over the southern half of the forecast area in a region of modest WAA and moisture advection at the leading edge of a 50-60kt LLJ at H8. The moist llevel airmass has resulted in fog over the cold ground/snowpack as dewpoints have moved above the freezing mark. The surface map also reveals another cold frontal boundary further to the north...draped south and west of a larger region of low pressure over the boundary between New Brunswick and Quebec. Arctic air is poised behind this boundary to advance towards the region today. Thus...primary forecast concerns center around morning precipitation chances and the impact of the arriving secondary front. Through Daybreak: Showers are finally arriving from the west...but are not terribly heavy and expect QPF to remain rather light. Do expect this activity to help thin the fog some...but some patches of locally dense fog are possible through the pre-dawn hours. Temperatures continue to be highly variable...but in general expect them to remain in the lower-mid 30s north and upper 30s through the lower 40s south through daybreak. Today: Weak wave of low pressure will be over the Gulf of Maine at 12Z...with southern frontal boundary sinking south away from the forecast area. This will allow rain showers to gradually sink south and out of the area...clearing the coast by mid to late morning. Robust dry advection doesn/t really arrive until late in the day...so we will likely be stuck with a decent bit of low level moisture into the afternoon. This will interact with arriving secondary front and modest low and mid level lapse rates to bring the potential for rain/snow /transitioning to snow/ showers in the mountains with sprinkles to the south and east. Thus expect skies to remain mostly cloudy with temperatures not having much success in moving...likely remaining steady from the mountains north...with modest warming to the south...with some low 50s possible over southeastern NH. && .SHORT TERM /Tonight and Saturday/... High Impact Weather Potential: Gale force wind gusts over the waters outside of Casco Bay...otherwise none. Pattern: A quiet period looks to be in store as short- lived...but robust shortwave ridging moves across the region with a brief return to a continental polar airmass. Primary concerns through this period therefore center around temperatures as well as gusty northwest winds on the leading edge of high pressure Friday night. Tonight: Shortwave ridging builds in from the west with surface high pressure arriving on our western doorstep by daybreak Saturday. PWATs rapidly drop below 0.1" overnight. Expect a few mountain snow showers to linger into the evening...but otherwise expect a precipitation-free night. Robust northwesterly winds will be ongoing this evening as isallobaric component aligns nicely with H9 winds of 35 kts to produce winds of 15-25mph with primary limiting factor being time of day. Guidance has trended slower in the arrival of high pressure from the west...with coupled boundary layer flow likely to continue through much of the night...with some valleys potentially decoupling just as we reach daybreak. Thus...there has been a similar uptick in the guidance temperature forecast and will trend the forecast just a tad warmer...but still a much colder night is expected...with single digits in the mountains and temperatures in the teens over southern NH and along the coast of Maine. As for skies...expect full clearing given the arriving subsident regime and aforementioned dry airmass. Saturday: We see a very brief respite in the active weather on Saturday as high pressure moves overhead during the morning hours to a location south of Nova Scotia by Saturday evening. While skies should be clear to start the day...expect increasing upper level cloudiness...particularly during the afternoon as top-down saturation commences ahead of next fast-moving northern stream shortwave. T9s begin warming during the afternoon as WAA regime sets up reaching the -5 to -9C range by afternoon. While we might not realize all of this as these values will be reached late /with increasing clouds/ in the day...20s north to lower/middle 30s south look reasonable. Expect light northwesterly winds in the morning to shift southerly but remain light through the afternoon given the proximity of departing surface high. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Low pressure moving northeast well south of the region will bring a light to moderate snowfall to much of the region Saturday night into Sunday morning. Although models have varied on the exact track and snowfall amounts, it now appears that an advisory level snow is becoming more likely across southern and coastal sections. The snow should move in quickly during the late evening with the heaviest snow falling between about midnight and 6 am. The storm departs quickly Sunday with clearing skies expected across southern areas by midday. Clouds will likely linger longer across the mountains with a developing northwest flow. High pressure will build across the region Sunday afternoon and move offshore Sunday night. This will allow a warming southerly flow to develop across the region starting Monday and continuing through at least mid-week. Initially, the warmer air will override some cooler at the surface leading to a period of overrunning showers Monday night into Tuesday. At the same time, a very slow-moving cold front will be moving east. At this time, it looks Maine and New Hampshire will remain on the warm side of the front through Wednesday night leading to some rather mild February temperatures and a continuation of showery weather. The front is expected to cross the region Thursday with cooler air slowly filtering into the region behind the front. Still, for February standards, Thursday`s temps will be well above normal. High pressure will follow the front for Friday. && .AVIATION /06Z FRIDAY THROUGH TUESDAY/... Short Term... Summary: A frontal system will move through the region through daybreak with showers and areas of fog. High pressure will build in behind this system for today...cresting over the region early Saturday before pushing offshore during the day Saturday. Restrictions: Area of showers moving into the terminals from the west over the next 2-4 hours with occasional LIFR/IFR fog ahead of it...with MVFR/IFR restrictions likely in SHRAs through early morning. Showers end with improvement to VFR during the day today...but a few afternoon sprinkles...additional showers possible. However...expect these to remain largely VFR. VFR tonight through Saturday. Winds: Winds will remain light through the night and the first half of Friday before strengthening to 12g20kts from the northwest late today and continuing through tonight...while slowly weakening. Winds Saturday will shift from light northwesterly early LLWS: Southwesterly winds at 2kft are weakening as of this writing...with the LLWS threat coming to an end and no further LLWS expected through this forecast period Saturday. Long Term... IFR to LIFR conditions developing Saturday night in snow, especially across southern and coastal areas. Conditions improving to VFR Sunday through much of Monday. MVFR to IFR conditions are likely again Monday night through Wednesday in showers with IFR conditions possible during the each night in showers and fog. && .MARINE... Short Term...Frontal system passes through the waters this morning with northwesterly winds developing behind this front this afternoon and strengthening through this evening with gale force wind gusts likely outside of Casco Bay. Winds/waves subside late tonight and through Saturday as high pressure moves overhead. Long Term...SCAs are likely Saturday night as low pressure moves south of the region. Winds will diminish and seas will subside a bit Sunday night but SCAs will likely develop again Monday as a southerly flow strengthens across the waters. The southerly flow will likely continue through Wednesday night. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory from 4 PM this afternoon to 7 AM EST Saturday for ANZ153. Gale Warning from 6 PM this evening to 7 AM EST Saturday for ANZ150>152-154. && $$ SYNOPSIS...Arnott NEAR TERM...Arnott SHORT TERM...Arnott LONG TERM...Jensenius AVIATION...Arnott/Jensenius MARINE...Arnott/Jensenius

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