After witnessing the tragic flooding in Washington this month, I couldn't help but wonder about the relationship between this very wet winter in the Pacific Northwest and La Niña. I knew the flooding was caused by a series of atmospheric rivers, but I wasn't sure how they were developing. Over Slack, I asked senior meteorologist Jonathan Erdman, "Does La Niña cause atmospheric rivers?"

Jonathan Erdman: In a "typical" La Niña winter, the Pacific Northwest is wetter than usual, while Southern California and the Desert Southwest are drier than average.

La Niña is the periodic cooling of water in the eastern and central Pacific Ocean near the equator. We see an average of one La Niña episode every three years or so.

Weather in your inbox

Forecast Location

Sign Up

By signing up you agree to the Terms & Privacy Policy. Unsubscribe at any time.

You might think that the flooding we’re seeing in Washington this month would be a perfect example of that. It certainly may have had some impact.

But a study published earlier this year found atmospheric rivers are significant wild cards that can overwhelm this nice and neat picture of La Niña.

For example, two years ago, California was clobbered by nine separate atmospheric rivers, which triggered deadly flooding and hundreds of landslides. That happened during a La Niña.

The study explains that, “Scientists expect these rivers in the sky will become increasingly important sources of annual precipitation in the Western U.S. under climate change, potentially making El Niño and La Niña years stray even further from their typical patterns.”

That's one of many challenges with seasonal forecasting. Atmospheric rivers are predictable only a couple of weeks in advance. Just 1 or 2 strong atmospheric river events can make it a "wet season" in California. It's a bit of feast or famine.

In fact, the atmospheric rivers we're seeing this weekend are more directed at California.

Do you have a question to ask the meteorologists at Weather.com? Write to us at [email protected] and we’ll pick a new question each week from readers to answer.