Ask a Scientist

By Sarah Parsons

How will La Nina affect the weather this winter?

Because the tropical Pacific is getting colder, we’re anticipating that the La Niña will be in force this winter, so we expect conditions opposite to what El Niño would produce in the US. El Niño, an abnormal warming of the tropical Pacific, generally causes a strengthening of the jet stream across the North Pacific and a pattern of storminess that affects much of the southern United States. When you have a La Niña, the jet stream tends to be weaker—it’s shifted northward, and the southern part of the US is generally drier. There’s a tendency for more cold air to come into the northern Great Plains and the Pacific Northwest. There’s a lot more variability with La Niña, too; there are more ups and downs during the course of a winter season.

I would expect the southern states would be warmer than they were last year, and the northern Great Plains and the Pacific Northwest would be somewhat cooler. There is a tendency for the Pacific Northwest to have above normal precipitation—that would bode well for the ski areas of the Pacific Northwest as well as the northern Rockies. For the Southwest, though, it looks like it will be on the dry side this winter. We can’t say too much about what will happen in the eastern half of the country as far as precipitation goes. From the Mid-Atlantic on up to New England, you get almost anything.                           

—as told to Sarah Parsons

Vernon Kousky research meteorologist at NOAA’s Climate Prediction Center

Issue 25

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