Clear to mostly clear overnight. Lows in the upper 40s to low 50s. Wind from the north/northeast 10-15 mph.
High-pressure strengthens in the Pacific, producing sunny and warm weather Friday. A weak trough sliding over the top of the ridge will increase clouds Saturday with slight cooling close to the international border. High clouds will be noticeable for western Washington but highs will still reach into the upper 70s. The trough exits; a thermal trough surging into Oregon will bring a rapid warm-up Sunday, Monday and Tuesday to western Washington.
Father's Day, Sunday, will become quite warm with highs in the 80s. Sunday will be the warmest day on the coast and the Solstice arrives at 8:32 p.m. Summer officially starts, skies clear to sunny and the heat is on for Monday when the thermal trough slides inland for low to mid 90s south of Seattle and across the Cascade foothills. Monday is on track to be the hottest day with highs in the upper 80s, which will rival possible daily records (Sea-Tac Airport record for June 21st: 89°).
An onshore breeze develops Monday evening to cause approximately ten degrees of cooling for Tuesday. Mornings will begin with areas of low clouds before clearing to sun. Wednesday morning may bring areas of drizzle too. Highs will cool back to the 70s.