269 FXUS61 KGYX 200319 AFDGYX Area Forecast Discussion National Weather Service Gray ME 1119 PM EDT Mon Apr 19 2021 .SYNOPSIS... A large upper level trough and surface cyclone will track through New England on Wednesday and Wednesday night bringing widespread rain and snow to the region. The highest chance for accumulating snow will be across the higher elevations and far north, where several inches are possible. Gusty northwest winds will also be possible as the system pulls away to the north and east on Wednesday night. High pressure and mostly tranquil weather will then return for the end of the week and early this weekend before another storm system approaches by Sunday. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 1115 PM...I tweaked POP/sky/temps a bit based on current obs. Mostly just to cover current conds, but latest temps show decoupling occuring in a lot of the usual spots so have adjusted those valleys and other sheltered areas down a bit for mins, but low lvl moisture and resulting fog likely to limit a complete freefall. 745pm Update...Just some minor tweaks to temperatures and sky cover over the next few hours as scattered showers continue to wind down this evening. The rest of the going forecast looks to be on track. Previously... A weak upper level wave crosses the region this evening and tonight with diurnally driven convective showers this afternoon gradually waning after sunset. While showers have had a tough time standing up this evening an isolated thunderstorm can't be ruled out entirely which could bring gusty winds to near 30 mph and small hail. Tonight, the wave moves on with nice clearing behind it, which combined with weak high pressure at the surface will lead to nice radiational cooling and patchy valley fog tonight with lows in the 30s for most locations. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Another upper level wave crosses tomorrow as attendant low pressure over Quebec pushes a cold front across New England. Thus another round of rain showers is expected tomorrow, mostly over the mountains closer to parent forcing. Steepening lapse rates aloft with the wave may produce isolated thundershowers during the afternoon as well. Otherwise, winds will increase out of the southwest in the morning and back to the west through the day as the cold front crosses... with wind gusts up to around 30 mph. Temperatures will climb to near 70 over the lower elevations, but be more subdued in the 50s and low-60s over the mountains where rain and clouds are expected. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Overview: An upper level trough and surface cyclone will bring widespread precipitation in the form of rain and snow to the region Wednesday and Wednesday night. Gusty winds will also be possible Wednesday afternoon and evening, especially along the coast. Weak high pressure will keep the weather mostly quiet for the end of the week and the beginning of the weekend before another frontal system arrives late this weekend with increased precipitation chances returning. High temperatures will generally be at or below normal early in the period before returning to above normal by the weekend. Impacts: Slippery travel conditions will be possible across the north and higher elevations, mainly Wednesday night through Thursday morning due to wet snow accumulations. Along the coast, gusty winds may be capable of blowing around light weight unsecured objects on Wednesday and Wednesday night. Forecast Details: An upper level trough will move through the Upper Great Lakes on Wednesday morning before passing through northern New England on Thursday. A warm front will form and move through southern New Hampshire before stalling on Wednesday morning, which will allow temperatures to quickly rise across southern locations and provide some convective instability. While severe weather is unlikely, did add a slight chance of thunder for these locations within this forecast package. During this same time period, a surface cyclone will form and move across the Ohio River Valley before quickly moving to the northeast. The placement and strength of the upper level trough will ultimately have the largest impact on the track of the surface cyclone, which will play a large role in precipitation types. Deterministic and ensemble guidance has been trending to keep the trough less amplified, which has allowed for a eastward shift in the surface cyclone. Looking more closely, there is decent clustering within individual low location members of the ECMWF, CMC, and GEFS just offshore into the western Gulf of Maine. The GEFS continues to be the furthest east, which would favor a colder solution. This eastward trend in ensemble clusterings continues to increase confidence for accumulating snow across the mountains and far north. While this will likely be another elevation dependent system, there is the potential for at least some wet snow flakes to mix in across valley locations, especially Wednesday night as the departing low pulls down colder air from the north. Ensemble means show generally a 20-30 percent chance for at least one inch of snow as far south as Lewiston, with categorical probabilities across the north. These probabilities then drop off rather quickly when examining the chances for at least 3 and 6 inches and they become significantly more elevation dependent. It is important to note that these are based on the assumption of a 10:1 snow to liquid ratio, where in reality they will likely be lower given marginal boundary layer temperatures. As a result, kept both the highest chances for snow as well as the highest snow accumulations across the mountains and along the international border. As the cyclone makes its closest approach to the region, gusty winds will also be possible as the PGF increases, especially along the coast where they may gust up to 35-40 mph or so. Total QPF looks to range from around one third of an inch to one inch, with locally higher amounts possible across the White Mountains. The system will likely slow down and maybe even stall over southern Quebec and Nova Scotia on Thursday with cyclonic flow overhead allowing for continued chances for upslope snow and rain showers likely. Thursday will be a significantly cooler day with high temperatures only ranging from the 30s across the north to the 40s elsewhere. A few locations across the far north may struggle to break the freezing mark. In addition, gusty northwesterly winds will keep windchill values into the 20s and 30s for much of the day. Upper level riding will move across New England on Friday and Saturday, allowing temperatures to moderate and keep the weather mostly benign. Some upslope showers will still be possible across the far north and mountains though, especially on Friday. Another trough and area of low pressure may track through the region late this weekend and early next week bringing another chance for widespread precipitation. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Short Term...VFR prevails through tomorrow with a small chance of brief MVFR in -SHRA this evening and again tomorrow, most likely for northern terminals during the afternoon. Patchy valley fog may impact valley sites like HIE/LEB/CON tonight. Southwest winds gust to near 25 kts tomorrow before backing to the west late in the day. Long Term...MVFR/IFR conditions likely on Wednesday and Wednesday night due to low ceilings, gusty winds, and widespread precipitation. There will be the potential for an isolated thunderstorm, especially across southern New Hampshire terminals such as KMHT. Across northern terminals, rain will likely mix with or change to heavy wet snow on Wednesday night. MVFR/VFR conditions possible on Thursday across southern terminals as precipitation gradually ends but across northern and mountain terminals upslope showers of rain and snow will likely continue. Northwesterly winds may gust up to 35 kts, especially along the coast and higher elevations. && .MARINE... Short Term...Quiet over the waters through tonight, then south winds increase during the day tomorrow gusting to near 25 kts. Seas will likewise increase to 3-5 ft by tomorrow night. Long Term...SCA conditions likely late Wednesday and Wednesday night as southerly winds become more westerly and gust up to 25 kts as seas build to 4-6 feet. Gale conditions are then possible on Thursday behind a surface cyclone as westerly winds gust up to 40 kts with seas of 4-7 feet. Widespread rain is expected Wednesday and Wednesday night with an isolated thunderstorm also possible. && .FIRE WEATHER... A brief period of elevated fire weather danger is expected tomorrow as a dry southwest wind develops ahead of a crossing wave. During mid- to late-morning, we'll mix out through the low levels and lead to humidity dropping to 25-30 percent for much of the lower elevations coinciding with wind gusts around 25-30 mph. Further north and into western Maine, rain and clouds will keep humidity higher with lower fire weather danger. Humidity will recover nicely tomorrow night, then wetting rains are possible for much of the region Wednesday into Wednesday night. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ SYNOPSIS...Casey/Tubbs NEAR TERM...Casey/Cempa/Watson SHORT TERM...Casey LONG TERM...Tubbs AVIATION...Casey/Tubbs MARINE...Casey/Tubbs FIRE WEATHER...