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Jet stream shift means start of stormy season in the Northwest – and an end to ‘Blob Jr.’

Tim Durkan
Tim Durkan Photography
Sunset at Cape Disappointment in September 2019.

It’s been a dark and stormy week in the Pacific Northwest. Starting Wednesday, the region was pummeled with wind and wet stuff as series of weather fronts started pushing through the skies above us. KNKX weather expert Cliff Mass says that’s going to continue all weekend and into next week, before it lightens up a bit.

The contrast can be jarring, especially when you have the stunning crisp fall days of early October that we did this year, often with sunshine. But Mass says this is absolutely normal.


“This is a classic,” Mass says. “Very frequently the first few weeks, first two weeks generally, of October are sunny (with) maybe a few showers – but pretty decent.

“Then, the third week of October, it’s like the switch has been pulled and the storms start coming in. And that’s what happened in this case.”

The reason for this switch is the position of the jet stream, which is a current of strong winds that separate the warm air to the south and the cold air to the North. Storms tend to follow it.

Mass says early in the fall, the jet stream tends to be up in Alaska and Northern British Colombia.  

“But there’s always a time when the jet stream slips south and gets over us and all of the sudden we get into the fire hose,” Mass says. “And that’s exactly what happened this week. We’ve had one system after the other and some of them have been pretty strong, in terms of precipitation. And that’s what caused all of this rapid shift into this wetter pattern.”


The stormy weather has at least one positive side effect: it is stirring up the ocean and causing the 2019 marine heat wave in the Northeast Pacific to dissipate. Mass likes to call this phenomenon “Blob Jr.” (as it is similar to its predecessor, officially dubbed The Blob) and expects its demise to happen pretty quickly. He says the sea surface temperatures off the West Coast are already close to normal.

“I’m afraid it doesn’t look good for the Blob in the long term, as the storminess really mixes things up,” Mass said.

Mass notes that Blob Jr. definitely has influenced our weather. And it’s a huge concern for fisheries, as it causes toxic algae blooms and other effects that can harm the ecosystem and kill marine life.

“This summer was weird,” he says as low temperatures in the region registered at about 5 degrees above normal – the same as the increase in warmth on the sea surface nearby. But that is all coming to an end now.

“That’s all going to change now as the warm water switches to normal – we should (also) see our minima drop to normal levels,” he says.

Cliff’s Forecast:

“This is the dark before the dawn,” Mass says of this week. It will get brighter, but not till the middle of next week.

Friday: Showers coming in with some rain shadowing in the Puget Sound region, highs in the mid- to upper-50s.

Saturday: Another weak system comes through in the morning. More rain, highs in the mid-50s, showery. Substantial snow in the mountains.

Sunday : A warm front comes through in the morning. More rain, but warmer in the morning. Highs in the mid-50s.

Monday: Another system comes in, more rain.

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