The large swath of cooler Pacific Ocean water south of the equator, indicated in blue in this June 2022 image, strongly suggests that another La Niña is on its way.

The National Weather Service on July 14 increased the odds that a La Niña will prevail for a third straight winter, a climate phenomenon linked to ample Northwest snowpacks.

A La Niña has a 66% chance of being in place by early winter, according to the service’s Climate Prediction Center. A month ago, the center pegged the chances at 59%.

“I wouldn’t say it’s a wholesale change,” Washington State Climatologist Nick Bond said. “If we’re talking about next winter, it’s still a long ways away.”

During a La Niña, cool sea-surface temperatures in the Pacific Ocean trigger changes in the tropical atmosphere. A La Niña formed in September 2020 and has persisted except for a brief period in 2021.

A La Nina influences weather worldwide. In the continental U.S., La Niñas are associated with cooler and wetter winters in the northern tier, but drier and warmer winters in the southern tier.

An El Niño, triggered by above-average ocean temperatures, has opposite effects. The Climate Prediction Center sees almost no chance that an El Niño will form next winter.

The center says there’s a one-third chance sea temperatures will be close to normal. The center evaluated about two dozen climate models and predicted sea temperatures next winter will be 0.5 to 1 degree Celsius below average, cool enough to cause a weak La Niña.

Since 1950, a La Niña has prevailed for three straight winters twice — from 1974-77 and then between 1998-2001.

The winter of 2000-01 was not good for Washington summer irrigation. The statewide snowpack on April 1 that year was only 61% of average.

Bond said climatologists have little precedent to make judgments about the potential strength of a a third straight La Niña.

“I still don’t think it’s going to necessarily be a really strong event,” he said.

Also July 14, the U.S. Drought Monitor released its weekly report. The northern tier of the West is in better shape than the southern tier.

Only 8% of Washington is in a drought, the lowest percentage in the West.

Some 67% of Oregon is in drought, while 45% of Idaho is in a drought. California, Arizona, Utah and New Mexico are entirely in a drought.

Droughts in East Africa and southern South America have the hallmarks of a La Niña, according to the World Meteorological Organization, an agency of the United Nations.