For the third year in a row, the United States is facing another La Niña winter.
Triple-dip La Niñas are rare – they’ve only been observed two other times in the past 72 years. But what was once rare could be the new normal (at least for a while), according to a recently published study.
“The Pacific Ocean naturally cycles between El Niño and La Niña conditions, but our work suggests that climate change could currently be weighing the dice toward La Niña,” study author Robert Jnglin Wills, a University of Washington research scientist, said in a university writeup of his study’s findings.
The new research is particularly interesting because it’s been long thought that rising global temperatures favor an El Niño climate pattern. (In the simplest terms possible, it’s because El Niño comes from warm sea surface temperatures, while La Niña happens when sea surface temperatures are cooling.) That’s still true in the longterm, but the opposite has been true in recent history, the study found.
Since 1979, as global temperatures have risen, sea surface temperatures have cooled in the southern Pacific Ocean. Those cooler waters interact with the jet stream to create La Niña conditions and affect our weather here on land. Broadly speaking, La Niña years are associated with cold, wet conditions in the north; warm, dry weather in the south; and strong hurricane seasons in the Gulf states.
Eventually, Wills explained, those waters will heat up and the trend will be reversed, giving us more back-to-back El Niño years.
In its most recent advisory, the National Weather Service’s Climate Prediction Center said there’s a 91% chance La Niña conditions last through November, impacting fall weather around the country.
What happens after November is less certain. Current models have the odds of La Niña continuing even longer at about 50%.
A third consecutive La Niña year would be harshest out West in states already suffering a bad drought. Places like California get most of their rain in the winter, and a La Niña winter could bring drier conditions to much of the state.
A La Niña winter likely means less rain or snow for the whole Southern half of the country, from the southwest through Texas, the Gulf and Florida. Meanwhile, it could bring colder, wetter conditions to the Pacific Northwest.