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Thank the ‘omega’ pattern for locking in another week of clear blue skies and sunshine

Tim Durkan
Tim Durkan Photography
On Tuesday, April 7, the Super “Pink” Moon rising over Seattle.";s:

It’s been warm and sunny lately with clear blue skies and great visibility in the Pacific Northwest — ideal for seeing for events like the supermoon Tuesday night. 


Contrast that with Southern California, where a pattern of rain and snow in the mountains has locked in, providing much-needed water for reservoirs, but dampening spirits for some who live there.

This contrast is due to a configuration in the atmosphere called a blocking effect, says KNKX weather expert Cliff Mass. 

“What has happened is a ridge — an area of high pressure — has built over the coast. And on both sides of this there are troughs of lower pressure,” Mass says. “This pattern is very stable and it can hold in for days.”

It’s called “omega,” after the Greek letter, whose shape resembles, “sort of like a horseshoe.”

The pattern began earlier this week and Mass says it will continue through the end of next week, with just a short break for some clouds and showers Saturday morning. 

It’s also responsible for the resurgence of the so-called “blob” of warmer surface waters off the West Coast. A past event of this kind built from 2014-16, damaging salmon runs and other seafood and posing threats to the ecosystem.

Mass says this blob is too far offshore to worry much about right now, but it’s worth keeping an eye on. In the meantime, he says we can all look forward to increasingly balmy weather the week ahead progresses.

“Temperatures will slowly increase to the mid-60s, maybe even the upper 60s by the time we get to Wednesday,” he says. “So, an absolutely delightful week.”

Listen above to hear the full discussion. 

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