Cooler sea surface could bring harsh winter

THURSDAY, AUG. 19, 2010

Last winter, our weather was influenced by El Niño, the warmer-than-normal sea-surface temperature in the south-central Pacific Ocean. During El Niño, we often have milder winters with less snowfall because the subtropical jet stream becomes stronger as moisture often flows along that path into California, the desert Southwest, Texas and the Deep South. This was the case last winter.

Within the last month, sea-surface temperatures near the west coast of South America and along the equator have been cooling at a rapid rate. This turn of events indicates a weak-to- moderate La Niña sea-surface temperature pattern, the opposite of El Niño. The latest data indicates that cooler waters are expanding near the west coast of South America. Ocean temperatures near Ecuador and Peru are now about 3 to 5 degrees below normal and are continuing to show signs of additional cooling.

During La Niña, the maritime polar jet stream often becomes stronger and the subtropical jet stream is much weaker. The northern U.S., including the Inland Northwest, usually receives higher snowfall totals and colder temperatures. This was the case during the winters of 2007-’08 and 2008-’09, as all-time record snows were reported across the northern U.S. and southern Canada.

Prior to the late 1990s, it would often take several years for sea-surface temperatures to flip from El Niño to La Niña. Within the last 10 years, though, we’ve seen sudden changes from El Niño to La Niña and vice versa, sometimes in mere months. This is another example of our cycle of wide weather extremes, the worst such period in at least 1,000 years.

The Southern Hemisphere is in the later stages of an unusually harsh winter, so it’s possible that we may see further cooling of the equatorial waters between now and October.

During the harsh winters here in the Inland Northwest, solar activity was low. Within the last few months, solar storms on the sun have been increased. At this point, it wouldn’t be enough to offset La Niña’s influence. However, if sunspot activity makes a big jump later this year, then it’s likely that this winter won’t be as severe as the snowy and cold winters of 2007-’09.

The fall rains should begin in late September and early October. Frosts and freezes will also be possible, even at the lower elevations, by early October.

With the new La Niña, the upcoming winter should be much colder and snowier than normal.

Contact meteorologist Randy Mann at randy@longrangeweather.com.

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