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David Sparks Ph.d La Nina
by David Sparks Ph.d, click here for bio

Program: Idaho Ag Today
Date: November 20, 2017

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The National Weather Service has declared that La Nina conditions are officially here. Forecasters say there’s now about a 65 to 75 percent chance that La Niña conditions could continue through the winter.

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

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

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 with 3-4 day intervals ever since.

"Last year, was an unusual year that we had cold temperatures. And then by February, we started getting a lot more snow in the high country and had some record high-levels," said Ron Abramovich of the Natural Resources Conservation Service.

All the El Nina indicators point to a similar winter as last year. But experts say that a lot of things have to line up to top a year like last year.

"Storm after storm came and the precipitation in the Boise Basin was 2.5 times normal last year," said Abramovich."The Big Wood Basin received 5 times normal precipitation in February.” Nearly 40 inches of snow fell in Boise from December through April while Pocatello had more than 86 inches, that's second-biggest winter on record rivaling the winter of 1948 In Bannock County.

Abramovich says that all that snow last year came from the La Niña weather pattern. El Niño and La Niña are opposite phases of what is known as 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 it's a classic course 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 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 give no guarantees about the storms heading our way

"Are they going to hit Oregon, Washington, the Cascades or are they going to come through California again and nail southern Idaho,” that's what Abramovich wants to know.

“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 he doesn't think that Idaho will have the same epic winter as last year.

"We'd be hard-pressed to see back-to-back rainfall patterns like what we saw last year,” said Abramovich. “But we’re going to get storms.”

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