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Why Is Northwest Weather So Hard To Predict? (Hint: It's Not, Anymore)

Tim Durkan Photography

You may have heard that predicting the weather in the Pacific Northwest is especially difficult. 

KPLU weather expert Cliff Mass says that may have been the case in past decades. But the truth now is, it’s not.

"In fact, that’s one of the great fantasies of the weather world: that somehow it’s really hard to predict here, the skill is much less than other places, because of the big Pacific," Mass said. "That’s, in fact, not true."

An Ocean's Influence

He says the ocean is a big factor and has always has been. Its influence on the weather is huge.

"And if you go back 30 to 50 years ago, we didn’t have much information out there," he said. "We had a few boats that were reporting weather information and a few islands that were launching weather balloons, but there wasn’t much. So we didn’t have a good idea what the storms were, what the fronts were, what the winds were like, out over the ocean,"

But, that has all changed, he says. And now we have a whole constellation of weather satellites that are looking down and giving us more than just the pretty pictures you see on TV every day.

"They can sense how temperature and humidity change with height. They can figure out what the winds are near the surface, by looking at the surface waves. They can measure the wind speed of clouds at various levels. So right now we have massive amounts of information out over the ocean. And that has resulted in dramatically improved weather prediction," Mass said. 

Mountains Make For Complex Meteorology, But They're A Constant

Mass says the two mountain ranges to the east and west of the Puget Sound do make the weather complicated in the Northwest.  We have all kinds of local weather effects, like the Puget Sound convergence zone caused by the Olympics.

"That’s when the air goes around the Olympic Mountains and converges over the Sound, giving us localized clouds and precipitation. We also have strong winds in gaps like the Columbia Gorge or the Fraser River Valley," he said. 

"So we have all these local weather features, but it turns out that they’re relatively predictable," Mass said. "The mountains? They stay put, they don’t go anywhere. And our computer models are really good at taking the large scale weather conditions, which we can forecast because we have all these observations over the Pacific Ocean and then to translate that to what the local weather features will be."

So while we may have very complex meteorology, it’s actually very predictable.

Fewer Thunderstorms Mean More Predictability

A final reason why forecasting in the Pacific Northwest is relatively easy is the lack of thunderstorms. 

"It turns out that thunderstorms are very infrequent here because of the cool Pacific Ocean," Mass said. "And thunderstorms are amazingly difficult to forecast. So, back east, (in the) central and eastern part of the United States, they have these massive squall lines, big thunderstorms, tornadic storms. They have all the severe weather that’s due to the instability of the atmosphere. We have almost none of that.  And that kind of weather is extremely hard to forecast – even a few hours ahead of time."

The bottom line? 

"Our weather forecasting here is actually fairly skillful," Mass said, "much more skillful than a lot of people think."

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 bpailthorp@knkx.org.