3rd year of La Niña, what does it mean for weather forecasts?

Written by oregonlive.com on September 19, 2022. Posted in Current News

The Northwest US should brace for another year of La Niña as the stubborn climate pattern in the tropical Pacific is expected to persist for a third consecutive year, forecasters say.

The latest outlook, published earlier this month by the National Weather Service’s Climate Prediction Center, follows on the U.N. weather agency’s August prediction of a “triple dip” La Niña — the first this century — caused by three straight years of its effect on climate patterns like drought and flooding worldwide.

The weather service has increased the chances of La Niña sticking around through November to 91 percent, a near certainty. The certainty drops farther into winter, with an 80 percent chance of La Niña from November to January and a 54 percent chance from January to March.

La Niñas are known to result in wetter, snowier conditions in parts of the northern U.S. , more frequent tornadoes in the south-central U.S. and increased Atlantic hurricane season activity. La Niña conditions typically mean cooler and wetter weather on average in the Pacific Northwest as the jet stream moves in from over the Pacific.

La Niña is the cooler phase of the El Niño-Southern Oscillation climate pattern and is a significant driver of weather conditions across the globe, including temperature, rain and snowfall, jet streams and tropical cyclones.

The World Meteorological Organization in late August said the cooling La Niña conditions have strengthened in the eastern and central equatorial Pacific with an increase in trade winds in recent weeks.

The agency’s top official was quick to caution that the “triple dip” doesn’t mean global warming is easing.

“It is exceptional to have three consecutive years with a La Niña event. Its cooling influence is temporarily slowing the rise in global temperatures, but it will not halt or reverse the long-term warming trend,” WMO Secretary-General Petteri Taalas said.

La Niña is a natural and cyclical cooling of parts of the equatorial Pacific that changes weather patterns worldwide, as opposed to warming caused by the better-known El Nino — an opposite phenomenon. La Niña often leads to less rain and more wildfires in the western United States, and agricultural losses in the central U.S.

Studies have shown La Niña is more expensive to the United States than the El Nino.

In the southwestern United States, La Niña seasons tend to be drier, which could spell trouble for the drought-ravaged region.

“It doesn’t mean for sure, 100 percent it’s going to be dry, but it does tilt the odds toward dry,” said Mike Halpert, deputy director of the Climate Prediction Center. “If you had been wet for a while now, drier than average wouldn’t matter — but it becomes very significant this year because of the drought that’s already in place. Another dry winter is certainly not going to be good news for California.”

Should the forecast manifest, it would be only the third time La Niña has stuck around for three consecutive years since records began in the early 1950s, Halpert said. The only other such “triple dips” were from 1973 to 1976 and from 1998 to 2001.

On the U.S. West Coast, La Niña can also reduce the number of atmospheric rivers, which could be worrisome in California, which receives much of its precipitation in the winter. A dry season this year forced officials to slash allocations from the State Water Project to just five percent.

Halpert said the relationship between ‘human-caused climate change’ and La Niña remains a topic of interest.

“La Niña and El Niño have existed for hundreds, thousands, of years we think, so it’s not like ‘climate change’ has any manifestation on the actual phenomena,” he said. “A more relevant question is, is ‘climate change’ changing the frequency of the two events, and to be honest, that’s really still an open research question.”

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Header image: NOAA / PMEL

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