Wednesday, November 15, 2017

Another La Nina Winter?

Winter shaping up, La Nina Could bring another big snow year

Boise-The National Weather Service declared this week that La Nina conditions are officially here.

Forecasters say there’s at least a 65-percent chance that La Niña conditions will continue through the winter.

"Last year, was an unusual year because we had cold temperatures. The last week of January we started getting a lot more snow in the high country and it kept snowing and we had record high-snowpacks" said Ron Abramovich of the Natural Resources Conservation Service.

Things are shaping up very much like last year. Fast moving storms have been hitting the Gem State in 3-day intervals since the first of October.

In Idaho, the La Niña weather pattern is known for bringing above-average precipitation to the state while delivering below-average precipitation to Northern and Southern California.

“Last year's season started with a pattern similar to what we're seeing this year as indicators are pointing to another weak La Niña this fall,” said Abramovich. But the veteran NRCS forecaster doesn't think that Idaho will have the same epic winter as last year.

"Storms came through and the precipitation levels last winter in the Boise Basin was 2.5 times normal," said Abramovich."The Big Wood Basin received 5 times normal precipitation in February, It’s going to be hard to duplicate that,” said Abramovich.

Nearly 40 inches of snow fell in Boise from December through April while Pocatello had more than 86 inches, that's the second biggest winter on record, rivaling the winter of 1948 In Bannock County.

La Nina is the cousin of better-known El Niño and known for it’s cooling of the equatorial waters in the eastern and central Pacific Ocean and that impacts atmospheric conditions throughout the world.

Idaho has already started seeing the effects of El Nina. Tamarac Ski Area outside of Cascade had a two-day, 20-inch snowstorm on the November 3rd weekend. Smaller storms have blown through and snowpacks are building in the mountains.

Abramovich says last years record snowpack came from the La Niña weather pattern. El Niño and La Niña are opposite phases of the El Niño Southern Oscillation - that's the fluctuation in temperatures between the ocean and atmosphere in the eastern Pacific along the equator.

In normal seasons atmospheric pressure pulls trade winds westward toward East Asia. During El Niña seasons the trade winds weaken, allowing the warmer water to shift east and taking the potential for strong tropical storms with it.

Typically, La Niña follows an El Niño event and Abramovich says its a classic weather correction.

La Niña will show ocean temperatures in the eastern Pacific that are cooler than average. It allows a ridge of high pressure to settle along the West Coast of the United States, pushing the polar jet stream further north and pulling the Pacific jet stream through Idaho and all that moisture with it.

La Niña years usually translate into cooler-than-average temperatures across portions of the Northwest.

So Southern Idaho could once again see cooler-than-average temperatures. When it comes to precipitation, Idaho is on the fringe of a wetter than average winter. But, the Northern Rockies could see another winter with above normal rain and snowfall.

But even with expectations from the National Oceanic and Atmospheric Administration Climate Prediction Center, experts have no guarantees about the storms heading our way.

"Are they going to hit Washington and the Cascades or are they going to come through Oregon and Northern California again or nail southern Idaho,” said Abramovich. That's what he and fellow NRCS forecasters want to know.

“Again, we’d be hard-pressed to see back-to-back rainfall patterns like last year,” said Abramovich. “But I think we’re going to get storms.”

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