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No rain for days in the Northwest. And a primer on how Earth’s atmosphere formed.

Erin Hennessey
A sunset seen from Bellingham Bay, Wash.

Light clouds and blue skies greeted most folks in the Puget Sound region Friday morning, and those conditions were expected to stick around all weekend long and into early next week.

Lots of lovely days are in the forecast, says KNKX weather expert Cliff Mass.

“We have a ridge of high pressure that has built in over the region and should stay at least until late on Tuesday,” said Mass, a professor of atmospheric sciences at the University of Washington in Seattle. “So that means no rain, no snow, no storms, no nothing.”


Mass says the only negative that comes with this kind of ridge is the possibility of persistent morning fog.

“When you have high pressure over us, we have sinking air that prevents the mixing of the atmosphere. And so, lower areas like the south (Puget) Sound can get fogged in. And it’s even possible we can get fog north to Seattle and Everett,” he said.

But the fog will tend to burn off in the late mornings, giving way to sunny afternoons. And the ridge, as well as the dry conditions it brings with it, are expected to persist until late Tuesday, at least.


“There’s no precipitation in the forecast. Temperatures should get into the upper 40s – maybe even lower 50s on a few of the days. Our snowpack’s pretty good. So, you get up on the mountains, that should be fine. That’s what we have to work with,” Mass said.


This week, Mass’ mind was fixed on atmospheric conditions of a very different kind. The professor gave a lecture Thursday on one of his favorite topics: how the earth’s atmosphere formed and how it evolved to become what it is today.

“The atmosphere has radically changed over the last four and a half billion years,” Mass notes. “And it’s very different than the atmosphere of the other planets.”

It started out as mostly hydrogen and helium — which would be uninhabitable for humans.

“And one of the big issues is that life on the planet has radically changed how the atmosphere evolved,” Mass says.


The saga includes an object the size of Mars crashing into Earth, pushing out the atmosphere. Later volcanic eruptions created a new atmosphere and allowed the oceans to form.

Mass says it was bacteria from the oceans that turned abundant carbon dioxide in the air into oxygen, through photosynthesis.

“And eventually, we had land plants. So, between the plants in the ocean and on land, the oxygen levels started to rise,” Mass says.

He says about a billion years ago, Earth’s atmosphere had become very similar to what we have today.

“So if I put you in a time machine, you could have breathed the air then. But you couldn’t have breathed the air two or three billion years before.”

To hear the full conversation, you can click on the "play" icon at the top of this post.

Weather with Cliff Mass airs at 9:02 a.m. Friday, right after BirdNote, and twice on Friday afternoons during All Things Considered. The feature is hosted by KNKX environment reporter Bellamy Pailthorp. Cliff Mass is a University of Washington professor of atmospheric sciences, a renowned Seattle weather prognosticator, anda popular weather blogger. You can also subscribe to podcasts of Weather with Cliff Mass shows, viaiTunes or Google Play.

Bellamy Pailthorp covers the environment for KNKX with an emphasis on climate justice, human health and food sovereignty. She enjoys reporting about how we will power our future while maintaining healthy cultures and livable cities. Story tips can be sent to