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La Niña to blame for cold, snowy weather

As I mentioned last week, much of the planet continues to experience some kind of extreme weather. Here in the Inland Northwest, we saw the snowiest November in recorded history. Snowfall for the 2010-’11 season is well above normal in the Spokane and Coeur d’Alene area.

As of early this week, Spokane International Airport has received 43.3 inches. The normal for snowfall for a season in Spokane is 45.6 inches. In Coeur d’Alene, 62.5 inches has fallen, with a normal of 66.7 inches for the entire season.

The extreme weather conditions are, in part, the result of a rather strong La Niña – a cooler than normal sea-surface temperature event along the equatorial regions of the Pacific Ocean. Since the middle of October, La Niña has been strengthening at a rapid rate. Based on current data, it appears that this moderate or, perhaps, strong La Niña will be with us through at least early-to-mid 2011.

Last year, we had a moderate El Niño, the warmer than normal sea-surface temperature event. Snowfall totals for the 2009-’10 winter season were well below average, and milder air moved into our region from the south.

During the warmer El Niño events, the subtropical jet stream to the south usually becomes stronger and moisture flows along that path into California, the desert Southwest, Texas and the Deep South.

During the cooler La Niña event, the maritime polar jet stream to the north often becomes stronger and the subtropical jet stream is much weaker. The northern portions of the U.S. usually receive higher snowfall totals and colder temperatures. Because this La Niña is relatively strong, the northern polar jet stream has become so intense that the upper-level winds have been driven southward into California, bringing heavy valley rains and mountain snows to the entire state. This has been a very unusual pattern indeed for so early in their rainy season. Southern California has been dealing with flooding rains and mudslides. However, it does appear that the jet stream will finally move north in the upcoming weeks.

For the rest of this winter season, and if La Niña continues to maintain its strength, conditions in our area should still be a bit colder and snowier than normal as the polar jet stream remains relatively strong. However, I don’t think the second half of this winter will be as snowy as the first half, as the heavier snowfalls are expected to move to the east of our region. I’ll have more details later.

Contact Randy Mann at randy@longrange