Area Forecast Discussion
Issued by NWS Portland, ME

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000 FXUS61 KGYX 211133 AFDGYX Area Forecast Discussion National Weather Service Gray ME 633 AM EST Wed Feb 21 2018 .SYNOPSIS... Strong southwesterly flow ahead of an approaching cold front will result in a very warm day across the region with record high temperatures possible. The cold front will cross the region this evening with cooler air filtering in for tonight and Thursday. A weak weather system passing south of the region on Thursday may spread some light rain and snow to southern areas before high pressure builds overhead Thursday night through early Friday. A series of weather systems will move through the region beginning late Friday and continuing through the weekend with mixed precipitation and slick travel possible. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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630 AM...Main focus of this update is on the dense fog, and to extend the advisory until 15Z along the coast and in ME zone just inland of the coast. Fog is diminishing in some of the zones further west, but with the strong shallow inversion in place, will likely have to wait until the core of strongest winds abv the boundary layer move through closer to midday. Also tweak temps a but based on current obs, which are a little colder than forecast in may of the foggy spots early this AM. Still uncertain of how warm it will get in areas that hang onto the inversion and the fog thru the morning, but any changes to high temps were minor at this point, and day shift will have to monitor. Previously...Trying to crack the sfc inversion is a struggle early this AM, as warming aloft continues, but lack of any real flow in the colder air near the sfc keeps that very shallow inversion in place. Temps at elevations and in downslope areas have been in the 50s, and even low 60s overnight. Fitchburg, MA /KFIT/ was 63 at 08Z, while mesonet data shows temps in the 50s above 2K feet in the White Mtns. So, the big question remains is how much and how quickly does mixing, even to 950mb, occur, as that would produce sfc temps in the 60s at least, given those temps are 17-18 C. Srn NH, and perhaps the CT valley is likely to be the first to mix down, given that the strongest flow aloft reaches there earliest, and they were in the warm sector yesterday. As you head N and E, things becomes less certain. Early morning clouds and fog will be a factor limiting breaking the inversion early. There should be enough mixing to the top of the inversion to allow warming into the 50s almost everywhere, but along the ME coast and into areas just interior of the mid- coast, the marine influence will temper some of the mixing. So, ultimately, highs range from around 50, which will be areas right on the mid-coast and Penobscot Bay, to the mid-upper 50s areas just inland of the mid-coast, and into the ME mtns. Interior SW ME, and even the coast S of Portland /except for the beaches/, will make a run at 60, if not 65 further inland, which will also be the temp range across much of NH. The exception will be srn NH, especially Merrimack and Seacoast where upper 60s, and even some low 70s are possible. By afternoon, should see breaks of sun across most of the CWA as well. The front crosses the CWA late in the afternoon, and should see temps start to fall behind the front, which could produce a few SHRA in the mtns. Actually, any place that is stuck in the inversion through the day will likely shoot up to its high very late in the day in the mixing right behind the front.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... As the winds shift to NW behind the front, will see T/Td fall through the night. Some upslope SHRASN will possible this evening, but these will be quite light. Some partial clearing expected, especially in the N, but as the front stalls to our south, look for mid clouds to linger over southern zones. Despite temps falling through the night, mins will stay above normal, generally in the 20s to low to mid 30s across the warmer srn zones. Weak wave track from west to east along the front will cross the CWA late Thu, and this will produce some light precip over the srn third of NH, and perhaps York county ME. Boundary lyr temps will be on the milder and with sfc temps running in the mid to upper 30s, will see a mix of snow and rain. If there are any accums, the would likely occur in the hills of Cheshire and western Hillsborough county, where some spots could see an inch. Otherwise look for any morning sun in the nr half of the CWA to fade to mostly cloudy, with highs in the mid 20s to low 30s. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... High Impact Weather Potential: * Some slick travel potential in the mountains and foothills late Friday/Friday night. * Snow/mixed precipitation possible Sunday-Sunday night. Pattern: The highly amplified trough/ridge pattern across North America early this morning will not persist long as energy ejecting out of the western trough will work to flatten the eastern ridge with an onslaught of energy rounding a ridge in the central/eastern Pacific acting to re-invigorate the western North American trough. At the same time...the vortex that has been centered in the vicinity of Hudson Bay will continue to weaken and shift away from the CONUS. Thus an active...and relatively mild period of weather is expected in the long term. The Details... Thursday Night: Shortwave passes east of New England to open the long term period with 1042+ mb high settling briefly into Maine with frontal boundary south of the region. Expect clearing to be partial...with mid and upper level clouds continuing to stream overhead ahead of next shortwave ejecting out of western trough and riding into the Great Lakes by Friday morning. The setup poses a potentially challenging low temperature forecast with the clearest skies in the north likely allowing these locations to fall into the single digits. Further south...where there is the potential for thicker cloud cover...can see many areas remaining in the 20s. Friday - Friday Night: Next shortwave arrives during the day Friday...with precipitation gradually becoming less organized as llevel convergence along northward advancing warm front weakens given veering llevel flow. Given that cool high pressure will be centered over Maine to start the day...the warming trend during the day will be slow in the low levels with some indication of a damming signature. The surface/H8 freezing line appears rather well aligned such that a snow to rain transition with some freezing rain possible Friday evening over northern areas where temperatures will likely never reach above freezing. QPF is not particularly high given weakening forcing for ascent thus outside of some slick travel potential in the foothills and mountains...see no very significant impacts. Saturday - Sunday: The pattern repeats itself during this period with high pressure cresting north of the region on Saturday before a much stronger low pressure system moves into the Great Lakes late Saturday night into Sunday...with triple point low forming in the vicinity of the New England coast Sunday with warm advection-induced precipitation shield moving overhead on Sunday and continuing into Sunday night. This setup lends itself much more favorably to cold air damming /as indicated by previous forecaster/ and forcing for ascent is more robust although still weakening somewhat as primary low occludes well north and west of New England. Much will depend on the details of the potential triple point development as a stronger feature will help anchor cold air and favor a snowier scenario...while a weaker low would likely lead to more icing. A moderate QPF event appears most likely with ensemble probabilities favoring in excess of one half inch liquid...but little support for one inch. Monday - Tuesday: High pressure returns to the northeast to end the long term forecast period with cooler...albeit still seasonable temperatures aloft. Maintaining low PoPs /for snow showers/ in the upslope flow areas of the mountains is prudent at this range given residual moisture in the northwest flow. Even with the cool down aloft...temperatures will remain above seasonal norms with locations south of the mountains likely reaching the 40s. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... Short Term...Fog will linger through about 12-14Z, during which time there should be gradual improvement to VFR by mid-morning at all but KAUG/KRKD. KAUG will see fog linger through midday, while KRKD will be stuck in fog through most of the afternoon, although conds should improve to IFR to MVFR around midday. LLWS will also continue into early afternoon. VFR is expected at all terminals tonight, and all but KMHT/KPSM on Monday, where MVFR in light SNRA will produce at least MVFR Thu afternoon. Long Term...VFR through early Friday then deteriorating conditions with rain and snow showers likely allowing for restrictions late Friday and Friday night before VFR conditions work back into the region Saturday. IFR restrictions likely return in snow/mixed precipitation on Sunday as a strong low pressure system approaches from the west. && .MARINE... Short Term...Borderline WSW SCA winds with seas of 5-6 ft in the open waters can be expected today. The winds will shift NW this evening and will diminish late tonight. Long Term...High pressure builds north of the waters Thursday night and into the Canadian Maritimes on Friday with quiet winds/waves before weak low pressure moves north of the waters Friday night with high pressure quickly building back in to the north of the waters on Saturday. A stronger low pressure system will move northwest of the region on Sunday with a secondary low potentially forming along the New England coast. This will likely result in renewed small craft advisories...with gales not out of the question depending on the strength/location of secondary development. && .HYDROLOGY... Flood watch continues for the threat of ice jams over western New Hampshire. Rainfall amounts have been light...but dewpoints continue to climb and do expect a significant melt in the headwaters tonight and through Wednesday. Lesser threat exists to the east where less rain has fallen...there are less existing jams...and temperatures through tonight are cooler. && .CLIMATE... Record high temperatures are expected in the region today. *** February 21 Records Temperatures*** Portland Concord Augusta 59F - 1953 64F - 1872 52F - 1981 ***Warmest February Temperatures*** Portland Concord Augusta 64F - Feb 26, 1957 69F - Feb 24, 2017 60F - Feb 18, 1981 && .GYX WATCHES/WARNINGS/ADVISORIES...
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ME...Dense Fog Advisory until 7 AM EST this morning for MEZ007>009- 012>014-018. Dense Fog Advisory until 10 AM EST this morning for MEZ019>028. NH...Flood Watch through this evening for NHZ001>003-005-007. Dense Fog Advisory until 7 AM EST this morning for NHZ001-002- 004-006-010. Dense Fog Advisory until 10 AM EST this morning for NHZ014. MARINE...Small Craft Advisory until 5 AM EST Thursday for ANZ150>152- 154.
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&& $$ SYNOPSIS...Arnott NEAR TERM...Cempa SHORT TERM...Cempa LONG TERM...Arnott AVIATION...Arnott/Cempa MARINE...Arnott/Cempa HYDROLOGY... CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.