A broad and unseasonably strong ridge of high pressure aloft over the western U.S. will continue to allow for clear skies and dry conditions through Monday.

Within this broad high pressure area, a narrow surface trough of low pressure extending north through California and Oregon will help maintain light easterly air flow downsloping through the Cascade passes on Sunday.  This will allow afternoon high temperatures east of the Sound to exceed Saturday’s values (highs 76 at Sea-Tac and 79 at Olympia) by a few more degrees.

North of Seattle, we’ll see highs in the 70s except 60s over the islands and west from Port Townsend through Port Angeles.

The warmest areas Sunday will be through the foothills of the Cascades south of I-90… then south and west following along and south of I-5 and into southwest Washington where highs from 81-85 degrees will be common.

The level of warming might not be quite enough to push Sea-Tac to 80 on Sunday, but in all likelihood this will happen on Monday as the combination of the broad high pressure ridge and the narrow thermal trough of low pressure reach their maximum effect.   Monday will be the warmest day of this stretch, and of the year thus far.  However, records at the three primary reporting sites ( SEA, Olympia & Forks) look just too warm to be in jeopardy at this point for either Sunday or Monday.

Onshore flow commences Monday night and by Tuesday morning, more humid maritime air will be pushing in through the south Sound, infiltrating the rest of the area as the day wears on.  Tuesday will still be a partly cloudy and warm day with highs in the 70s for many, but by Wednesday and Thursday highs fall back into the 60s to around 70 under increasing clouds.

Rain chances look minimal until a slight chance of a few mainly mountain shows Thursday.