The autumn equinox was early Sunday morning. Welcome to the first full week of fall.

The weather this week will be a mix of late summer and early fall weather. Clouds covering Western Washington on Monday morning are expected to give way to sunshine in the afternoon as higher pressure builds over the region. Highs from the Puget Sound area south toward Portland are expected to rise above 21 degrees — near this week’s average highs, while northern interior and coastal regions will warm to above 18 degrees, also near average highs.

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Tuesday is expected to be the warmest day of the week, with temperatures in the west and plenty of sunshine reaching highs of 21 degrees. Tuesday will also see the last sunset of the year at 7pm.

Then comes the wetter fall weather. Two Pacific frontal systems are expected to move ashore and impact the rest of the work week. The first system is expected to bring light rain to the region on Wednesday, and the second, stronger system will arrive with more rain on Thursday.

Temperatures will be significantly cooler for the rest of the work week, reaching highs of only 15 degrees. Persistent rain showers are expected to ease by Friday. As a taste of fall, snow levels in the Cascades are expected to drop to nearly 6,000 feet on Friday, bringing a fresh dose of snow to the higher elevations.

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Higher pressure is expected to settle over the Pacific Northwest on the last weekend of September, bringing more sunshine and temperatures above 60 degrees. The Seattle Mariners return home for their final three-game series of the season against the Oakland A’s, with the stadium roof likely to be open. The Sounders and Reign also play next door at Lumen Field in dry weather over the weekend.

If the longer term forecast is accurate, the dry weather should continue into the first half of next week before wetter autumn weather returns later in the week. Overall, autumn has arrived and with it the mix of early autumn-like weather.

Ted Buehner is a meteorologist at KIRO Newsradio. Read more of Ted’s stories here and follow him on X.