La Nia's back. Here's how it will affect the weather

The Associated Press | Posted: October 15, 2021 3:50 PM | Last Updated: October 15, 2021

Colder winter weather expected in western Canada, more drought in southwestern U.S.

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Caption: County of Santa Barbara Fire Department firefighters extinguish a roadside fire next to train tracks off highway 101 in Goleta, Calif., on Oct. 13, 2021. On Thursday, the National Oceanic and Atmospheric Administration announced that a La Nia has formed, which can be bad news for parts of the parched West in the U.S. (Ringo H.W. Chiu/The Associated Press)

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For the second straight year, the world heads into a new La Nia weather event.

This would tend to cool western Canada, dry out parts of an already parched and fiery American West and boost a busy Atlantic hurricane season.

Just five months after the end of a La Nia that started in September 2020, the U.S. National Oceanic and Atmospheric Administration announced a new cooling of the Pacific is underway.

La Nia's natural cooling of parts of the Pacific is the flip side of a warmer El Nio pattern and sets in motion changes to the world's weather for months and sometimes years. But the changes vary from place to place and aren't certainties, just tendencies.

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La Nias tend to cause more agricultural and drought damage to the United States than El Nios and neutral conditions, according to a 1999 study. That study found that La Nias in general cause $2.2 billion to $6.5 billion in damage to U.S. agriculture.

How strong will it be and how long will it last?

There's a 57 per cent chance this will be a moderate La Nia and only 15 per cent that it will be strong, said Mike Halpert, deputy director of NOAA's Climate Prediction Center.

He said it is unlikely to be as strong as last year's because the second year of back-to-back La Nias usually doesn't quite measure up to the first.

This La Nia is expected to stretch through spring, Halpert said.

WATCH | What a La Nia year could mean:

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Caption: Johanna Wagstaffe says it typically means colder, snowier weather in the West

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What does this mean for the weather?

In Canada, La Nia tends to be linked to winter weather that includes above average precipitation in British Columbia, colder-than-normal temperatures in the Prairies and more rain and snow than average in Ontario and Quebec, according to Environment Canada.

For the entire southern third of the U.S. and especially the Southwest, La Nia often means drier and warmer weather. The West has been experiencing a two decade-plus megadrought that's worsened the last couple of years.

But for the Northwest Washington, Oregon and possibly parts of Idaho and Montana Halpert said La Nia means a good chance of rain and drought relief.

"Good for them, probably not so good for central, southern California."

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Caption: Floodwaters slowly recede in the aftermath of Hurricane Ida in Lafitte, La., on Sept. 1, 2021. The formation of La Nia could mean a more active Atlantic hurricane season. (Gerald Herbert/The Associated Press)

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The Ohio Valley and Northern Plains could be wetter and cooler. La Nia winters also tend to shift snow storms more northerly in winter while places like the mid-Atlantic often don't get blockbuster snowstorms.

In general, expect it to be cooler in western Canada, southern Alaska, Japan, the Korean peninsula, western Africa and southeastern Brazil.

Much of both southeast Asia and northern Australia are wetter in La Nia and that's already apparent in Indonesia, Halpert said. Central Africa and southeast China tend to be drier.

WATCH | Hurricane Ida quiets New Orleans as recovery efforts start:

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Caption: Hurricane Ida has almost silenced New Orleans, most of which remains without power or water, as recovery efforts start in earnest and residents try to cope.

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What about hurricane season?

During last year's La Nia, the Atlantic set a record with 30 named storms. This year, without La Nia, the season has still been busier than normal with 20 named storms and only one name left unused on the primary storm name list: Wanda.

The last couple weeks have been quiet, but Halpert said he expects things to pick up again. "Just because it's quiet now, it doesn't mean we won't still see more storms as we get later into October and even into November."

La Nias tend to make Atlantic seasons more active because one key ingredient in formation of storms is winds near the top of them. An El Nio triggers more crosswinds that decapitate storms, while a La Nia has fewer crosswinds, allowing storms to develop and grow.