Hello again, La Nina. As you continue to gain strength in the tropical Pacific Ocean, we ask that you not throw the Pacific Northwest into a harsh weather frenzy this winter.
La Nina, characterized by cooler than normal sea-surface temperatures in the equatorial Pacific, can significantly alter weather patterns worldwide.
Here in the Pacific Northwest, La Nina episodes tend to cause colder and stormier conditions during winter. The stronger they are, the more intense those conditions are likely to be.
And now, La Nina is looming large. The naturally occurring phenomenon is well established in the Pacific Ocean and is “expected to be moderate to strong” through January, the World Meteorological Organization announced late last week. The 2020-2021 La Nina is expected to influence precipitation, temperatures and storm patterns across the world, the U.N. weather agency stated.
Historical patterns suggest that if this La Nina gets strong enough, the Pacific Northwest will be cooler and wetter than normal, with more storms and mountain snow.
In contrast, two-thirds of the country, including Southern California and the entire South, would see a winter that’s warmer and drier than average.
That’s pretty much what the National Oceanic Atmospheric Administration’s Climate Prediction Center is forecasting: Our nation’s southern tier will remain mild and dry, while much of the Pacific Northwest and Upper Plains will see just the opposite.
La Nina is one of three phases of what’s known as the El Nina-Southern Oscillation. The other two are El Nino and a neutral phase. La Nina episodes are mostly weak to moderate in intensity and occur every three to five years. Among other things, their patterns influence the position of the jet stream flow over North America.
The last time a strong La Nina occurred was in winter 2010-11, when generally cold, wet and snowy conditions engulfed the Pacific Northwest. In Spokane, 25.9 inches of snow fell during November – a record for that month. A portion of it was dumped by a large winter storm shortly before Thanksgiving that brought record low temperatures and even a rare 2.5 inches of snow to Seattle. Blizzard warnings were issued for parts of Eastern Washington as the storm blasted across the state, where heavy snow, high winds and subzero temperatures made holiday driving especially risky.
As winter unfolded, active weather conditions persisted. By the end of the season, Spokane received nearly 70 inches of snow, compared with its average amount of 42 inches.
It’s important to note that our winter weather isn’t determined only by La Nina. Although a strong one certainly stacks the dice in favor of colder temperatures and more rain and snow for the Inland Northwest, it can still be a wild card. We could experience a season of cold snaps and snow mixed with drawn-out mild interludes instead.
Nonetheless, unlike day-to-day variations in the weather, this La Nina-influenced forecast is intended to provide a glimpse of what our overall winter is likely to look like, especially in the mountains where a strong snowpack is needed to replenish the region’s water supply.
If the forecast does pan out, you’ll be grateful for your sturdy shovel, heavy coat and water-resistant boots.
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