Area Forecast Discussion
Issued by NWS Portland, ME
Issued by NWS Portland, ME
100 FXUS61 KGYX 180639 AFDGYX Area Forecast Discussion National Weather Service Gray ME 239 AM EDT Fri Sep 18 2026 .WHAT HAS CHANGED... Little change to the going forecast early this Friday morning. && .KEY MESSAGES... 1. Any showers end prior to sunrise this morning. Areas of fog will lift quickly as mixing commences. High pressure moves in for tonight and Saturday with fair weather. Areas of of frost possible in mountain valleys in the north tonight. 2. Cooler than normal temperatures are expected next week. The front to our south will provide the focus for rain chances during the early part of the week. && .DISCUSSION... KEY MESSAGE 1 DESCRIPTION... A cold front and associated weak low pressure will move east of the forecast area early this morning. The showers are likely to move offshore well before sunrise. Thereafter, clearing quickly take place along with the quick dissipation of any fog. The balance of the day will feature warm temperatures, mostly sunny skies, and wind gusts of 20 to 25 MPH from the NW. SFC high pressure will impinge on the forecast area from the NW tonight which will allow the winds to become light. Portions of the northern mountains (valleys) may decouple enough to allow for radiational cooling that delivers lows in the 30s allowing possible areas of frost. 40s elsewhere. The SFC high crests over the forecast area on Saturday allowing for a lot of sun, lighter winds, and cooler high temperatures. KEY MESSAGE 2 DESCRIPTION... The highest confidence portion of the extended is that the pattern will generally favor high pressure locally thru next week. More than that high pressure is looking seasonably strong. Absent any cloud cover that will mean relatively shallow mixing during the day, and overnight ideal conditions for radiational cooling. The latest run of the NBM has daytime temps cooler than normal, staying in the 60s, while overnight plenty of 40s and mid to upper 30s in the usual colder valleys. I suspect frost will be possible, but that will be dependent on any cloud cover on individual nights. I do not plan to put any in the forecast at this range, but I want to mention it here as a threat. The cloud cover will be tied to the surface baroclinic zone. The high pressure should tend to keep that south of the forecast area, but that does not mean that any wave tracking along it can`t spread clouds and even rain/showers thru parts of the area. Given the strong ridge centered across the southeastern CONUS, the pattern is fairly favorable for a later season ring of fire. So the convective cycle could drive these waves, and will lead to lower than normal model confidence. Right now ensemble guidance likes one of these waves to pass near the forecast area Sun. The latest ECMWF Ens has roughly a third of the members dry for the northeastern half of the forecast area, and the GEFS has near a 50/50 split. The latest NBM run has an area of likely PoP sweeping along and south of a LEB to PWM line, so that is a fairly good match and I see no reason to alter it. Ensembles are also lighter on QPF than the ongoing event. We will welcome the rain but it does not look like a drought buster. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... Any lower cigs and vsbys early this morning improve between 09z and 13z with the passage of a cold front. VFR expected for the rest of the day with NW wind gusts of 20 to 25 kt at times. VFR tonight with valley fog, mainly in the CT River Valley. VFR with lighter winds on Saturday with high pressure overhead. Outlook... Saturday night: Generally VFR early with ceilings lowering after 06Z Sunday. Sunday: Areas of MVFR expected, especially southwest, with rain/showers. VFR possible north. Monday-Tuesday: Generally VFR expected. MVFR and showers possible especially south. Local IFR or lower possible overnight in valley fog. Wednesday: VFR conditions expected. Local IFR or lower possible overnight in valley fog. && .MARINE... A cold front will pass across the waters this morning. Wind gusts around 20 kt likely, with a few around 25 kt possible. Tranquil tonight and Saturday with high pressure overhead. Winds and seas generally expected to remain below SCA thresholds next week. Will have to watch for areas of fog developing near frontal boundary during the first half of the week. Seas may build to near 5 ft south of Cape Elizabeth by midweek. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...None. && $$ DISCUSSION...Ekster/Legro