Tropical waters have the potential to make Alaska’s winter colder than normal

The phenomenon is called a La Niña
Published: Sep. 13, 2020 at 11:16 PM AKDT
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ANCHORAGE, Alaska (KTUU) - A cooling of ocean water in the tropical Pacific Ocean could make Alaska’s winter a little colder and drier than normal this year. The phenomenon is called a “La Niña,” and is essentially the opposite of the more infamous “El Niño.”

“El Nino gets kind of all the attention when that happens,” said Brian Brettschneider, a climatologist with the National Weather Service, Alaska Region. “La Nina, not so much, because the reactions to La Nina or the effects of La Niña are kind of more muted than what we see with an El Niño.”

La Niña is characterized by unusually cold water in the equatorial Pacific Ocean, and the trade winds that blow from east to west strengthen.

But how could this affect Alaska’s weather this winter?

“We get this reflection at the surface," Brettschneider explained. “And because it’s the tropics, because the tropics have so much energy, that drives these tremendous thunderstorm circulations. When that warm water gets pushed all the way to the west, toward Asia, you get big thunderstorms that develop in the the western tropical Pacific and those thunderstorms send massive amounts of heat and momentum into the atmosphere.”

Brettschneider said these storms send a lot of air northward.

“It drives big high pressure over, say, western Asia. And then the response to that, because the atmosphere tries to maintain equilibrium, is we get a big dropping down to the air mass to the east of that, which is over Alaska,” said Brettschneider.

This means cold air from the north tends to get pulled down across Alaska.

“Typically in Alaska, we were on that cold side of the upper level flow,” Brettschneider said. "And generally, it’s a little bit drier as well.”

Brettschneider emphasized this isn’t a forecast, but instead the climatology of a La Niña, or a look back at the historical relationship between it and the winter weather patterns.

The good news for those who like a “good, Alaska-style kind of cold winter," Brettschneider said is that, historically, Alaska is the bigger winner during La Niña year for a good winter, even if the trend is toward drier conditions.

“Even if you have only two thirds of your snow, you end up with a really good, you know, base layer of snow for travel, for recreation, for subsistence,” said Brettschneider. “If you have a warm winter, even if it’s above normal snow, that can provide a number of hazards, again for travel, for recreation, when you get these kind of big, winter thawing events.”

The Climate Prediction Center issued a La Nina advisory for the coming winter which means that La Niña conditions are present and are likely to continue through the Northern Hemisphere winter. La Niña conditions occur on a fairly regular basis, between two to five years apart.

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