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La Niña roars back; more drought is ahead

Spring weather will be dry across most of the United States except for northern areas.

The second time is a charm for La Niña. It’s coming back in force for the spring and possibly the summer, bringing with it continued drought and targeting the southwestern corner of the nation, especially.

“This La Niña probably means bad news for the American Southwest, which should see lower than normal rainfall this winter,” says Josh Willis, a climate scientist at NASA’s Jet Propulsion Laboratory. “This La Niña may not be a whopper, but it’s still an unwelcome sign for an area already deep into a drought.”

In North America, cooler and stormier conditions during La Niña often set in across the Pacific Northwest, while weather typically becomes warmer and drier in the U.S. South and in northern Mexico.

The La Niña event that started in late 2020 fits into a larger climate pattern that has been going on for nearly two decades — a cool (negative) phase of the Pacific decadal oscillation (PDO). During most of the 1980s and 1990s, the Pacific was locked in a PDO warm phase, which coincided with several strong El Niño events. But since 1999, a cool phase has dominated.

The long-term drought in the American Southwest coincides with this trend, Willis notes. In a report released late in 2021, forecasters predicted La Niña conditions would persist through Northern Hemisphere winter, with a 60% chance the ocean would transition back to neutral conditions during the April-June period.

La Niña is linked to increases in the likelihood of above- and below-average precipitation over many regions of the globe. Changes in precipitation occur during certain times of the year. Over sub-Saharan Africa, primary rainfall seasons with wet conditions are in the central and eastern Sahel (June-September) and in Southern Africa (October-May).

Over Central Asia, dry conditions are most likely during the winter and spring precipitation seasons. In northern Central America and the Caribbean countries, the likelihood of wet conditions increases during July-September.

Stage is set for La Niña

Part of the El Niño-Southern Oscillation cycle, La Niña appears when energized easterly trade winds intensify the upwelling of cooler water from the depths of the eastern tropical Pacific, causing a large-scale cooling of the eastern and central Pacific Ocean surface near the equator.

These stronger-than-usual trade winds also push the warm equatorial surface waters westward toward Asia and Australia. This dramatic cooling of the ocean’s surface layers then affects the atmosphere by modifying the moisture content across the entire Pacific.

This La Niña coupling of the atmosphere and ocean alters atmospheric circulation and can cause shifts in mid-latitude jet streams in ways that intensify rainfall in some regions and bring drought to others.

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