What is La Nina, and what does that mean for South Dakota’s winter?

RAPID CITY, S.D. — The National Oceanic and Atmospheric Administration, or NOAA, issued their season outlook for the winter months of December through February on Thursday. It’ll be another La Nina winter, so this will be our second in a row.

Last year’s winter was warm and dry, and characterized by a weak La Nina. But as we know, each winter is unique and special, as Dr. Matthew Bunkers, Science and Operations Officer with the Rapid City National Weather Service explains.

“This La Nina this winter is looking to be stronger than last year’s, which would lead to more likelihood that we would have these systems or clippers coming out of the northwest bringing more cold air outbreaks than average and favoring a little bit more snow,” he says. The prediction for South Dakota based on these patterns is lower than average temperatures and precipitation that is normal or slightly above average.

Winter Outlook Seasonal Temperature 2021Winter Outlook Seasonal Precipitation 2021

So, we’re looking at a colder and slightly wetter winter, but what even is La Nina? Hang with me, we’re gonna get through this tropical meteorology ordeal together.

A La Nina event just means that the sea surface temperatures of the Pacific Ocean are colder than normal near the equator. Ocean temperatures drive global atmospheric patterns, because the atmosphere actually gets much of its energy from the ocean. Atmospheric motion is completely coupled with oceanic motion.

La Nina

So, a colder, less energetic ocean near the equator creates an imbalance in the energy of the ocean and atmosphere. More energy often comes out of the higher latitudes and moves towards the tropics to try to restore the equilibrium.

This energy movement from the north pole to the equator manifests as changes in the jest stream, which dominates South Dakota weather patterns. The jet stream is expected to sink down into South Dakota and Wyoming more frequently this winter, and it will bring wintry systems with it.

Jet Stream during La Nina

“La Nina favors more systems coming out of the northwest as opposed to the southwest, and because they would be coming from the northwest, that tends to bring winder, gusty northwest winds and colder weather, so it tends to be more frequent and of course we can have some intense cold air outbreaks,” Bunkers explains.

Whew! We made it out of the tropics. Now, we move on to one last important topic: drought outlook.

La Nina is strongly connected to drought conditions.

“One thing that La Nina does do is tend to favor drought conditions during the summer which we did see this last year,” he adds. “So, two La Nina years in a row could mean two dry periods in a row.”

If we maintain even slight drought conditions over the winter, the drying that takes place after La Nina could exacerbate existing drought issues next summer.

However, it’s also important to remember that this outlook covers meteorological winter, which is December, January, and February. Winter conditions can persist well past these months in South Dakota. We’ll continue to monitor current and expected conditions closely as the season develops.

Make the most of this winter by staying safe and warm, and enjoy the beauty where you can find it.

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