Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
512 FXUS61 KGYX 181821 AFDGYX Area Forecast Discussion National Weather Service Gray ME 221 PM EDT Tue Aug 18 2026 .WHAT HAS CHANGED... No changes were necessary to the ongoing forecast. && .KEY MESSAGES... 1. Some instability may lead to an isolated shower across the interior this afternoon. The next few nights will be foggy and Wednesday should stay mostly dry. 2. A weak boundary may bring a few showers Thursday, but otherwise mostly dry conditions are forecast through at least the first part of Saturday with seasonable temperatures. 3. The next chance for rain on a widespread basis arrives for the second half of the weekend. && .DISCUSSION... KEY MESSAGE 1 DESCRIPTION... Low pressure just offshore of Cape Cod will allow for gloomy conditions to continue across northern New England. A few isolated showers are currently seen across western Maine on the radar. Very stable mid-levels should limit convective activity this afternoon, but residual instability could allow for a few more isolated showers or thunderstorms to pop up across the interior this afternoon. Tonight, calm conditions persist across NH and western Maine, with marine fog and low stratus advecting into coastal areas. Fog will develop well into the interior, and continue through Wednesday morning. A front will move in from the Great Lakes on Wednesday, and will approach NH by Wednesday evening. Most places should stay dry, but an stray shower or storm could form ahead of the front. The storms attached to the cold front itself will probably be dead on arrival as CAMs show a decaying trend in the storms when they are over New York state. In addition, the front most likely won`t cross into the region until after sunset so there won`t be much energy to work with either. Patchy fog returns Wednesday night and will continue through Thursday morning. KEY MESSAGE 2 DESCRIPTION... There are a couple of features that may bring a few showers to the region on Thursday. The first is a weak frontal boundary crossing through the day while the second is a shortwave crossing southern New England that could bring an additional couple of showers along the coast and southern NH. Most will probably not see any rain but those that do will only see light amounts as QPF signals in the model guidance is limited to only a few hundredths. Otherwise, seasonal temperatures are expected with highs in the mid 70s to low 80s. High pressure then builds in Friday and the first part of Saturday, keeping the weather dry for much of the area. The high does move off to the northeast later Saturday as low pressure emerges off the Mid-Atlantic coast, and moisture will start to increase from south to north over northern New England, potentially enough for a few showers along the coast and southern NH during the day Saturday. But again, most will be dry as the better chances hold off until the second half of the weekend. Highs will in the 70s to low 80s and lows mostly in the 50s, except some embedded upper 40s. KEY MESSAGE 3 DESCRIPTION... This initial low will keep a chance for showers along the coast and southern NH Saturday night, but rain chances further increase areawide Sunday into Sunday night as a 500mb approaches from the west and encompasses much of the US East Coast. There`s a strong signal in the ensemble for most of the area to see measurable rain, although there are timing differences. If the 500 mb trough remains an open wave the rain looks more in the Sunday-Sunday night timeframe, but if it closes off, then a slower onset and end will likely be the result, making the higher rain chances more in the Sunday night and Monday window. By Tuesday, we should see a return to drier conditions, except there may be some upslope showers in the mountains. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... VFR is expected this afternoon outside of isolated showers that develop across the interior. Conditions will significantly degrade this evening as widespread patchy fog builds across NH and Maine. IFR and perhaps some LIFR is possible tonight in areas of denser fog. Visibility should improve quickly Wednesday morning, but low CIGs will hang on through much of the first half of Wednesday. Conditions look to improve to VFR by the end of the day, but this period of VFR will be short lived as fog redevelops over the area Wednesday night. IFR is expected with fog on Wednesday night and will not improve until after sunrise on Thursday. Outlook: Thursday: A few showers in the afternoon could produce brief instances of MVFR, but otherwise VFR. Thursday night-Saturday: Mainly VFR, except nighttime/early morning valley fog could produce IFR to LIFR at HIE and LEB. Saturday night-Sunday: Increasing chances for rain. IFR to MVFR possible. && .MARINE... Winds and seas generally stay below SCA levels. Winds will be light and variable through the end of the week. A brief window of elevated seas are possible late tonight, but the higher seas will likely be confined to the open waters offshore from Penobscot Bay. Seas recede on Wednesday. Outside of this window, seas of 2-4ft are expected through the rest of the week. Thursday-Tuesday...SCA conditions are currently not expected through early next week. A weak front crosses the waters Thursday and will be followed by high pressure building in Friday and the start of the weekend. The high shifts to the north and east as a couple of low pressures approach and cross the waters from the west and southwest during the late Saturday through Monday timeframe. High pressure returns by Tuesday of next week. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ DISCUSSION...Palmer/Combs