Climate Matters: La Nina may cool temperatures but could dry out the summer

After much of the world experienced the hottest year on record in 2024, the U.S. has seen a lot of cold and snow for January.

This warmth was partly fueled by a strong El Nino that peaked last year and was slow to come down. Now, changes are sweeping the nation as tropical Pacific Ocean temperatures have cooled to a weak La Nina for early 2025.

El Nino and La Nina are phases of a system between the atmosphere and ocean where ocean temperatures and weather patterns fluctuate and interact. This is formally known as the El Nino-Southern Oscillation and encompasses both the changes in the oceans and atmosphere.

El Nino (or La Nina) is observed over the Pacific Ocean near the equator where ocean temperatures warm and cool in highly irregular 2 to 7-year cycles. This leads to variations in air pressure (the Southern Oscillation) across the Pacific Ocean with local and global impacts depending on the strength of the event.

El Nino years typically see warmer temperatures, like in 2023 and 2024, as Pacific temperatures warm and the trade winds weaken. The opposite occurs during a La Nina event when the trade winds blow stronger and push cold water into the tropical Pacific.

The connections to this climate pattern abroad are loose, but impacts from this system can be identified in parts of the United States. El Nino influences hurricane activity in the warmer seasons while more specific precipitation and temperature trends can be identified in the winter.

El Nino encourages the jet stream to dip south in the winter with storms tracking further south across the Four Corners and the Gulf. This leads to cooler and wetter conditions in those areas while the north, especially the Pacific Northwest displaced from its usual storm track, is drier.

La Nina pushes the jet stream back toward the poles, drying out conditions to the south in winter while increasing precipitation in the Pacific Northwest and over to the Ohio Valley. This can sometimes include Central Missouri, but it is much harder to draw conclusions in our area.

Especially with a weak La Nina as we are currently seeing for early 2025, outcomes may not perfectly fit historical trends. Our previous weak La Nina from 2022 to 2023 led to near-average precipitation but warmer temperatures, dramatically reducing winter snow totals.

So far this January has been cold and snowy for much of the United States and seasonal outlooks are eerily similar to a La Nina setup. Above-average precipitation is favored near the Ohio Valley with cold favored further north and east while the South is drier and warm.