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The Spokesman-Review Newspaper
Spokane, Washington  Est. May 19, 1883

La Niña conditions could bring a bountiful skiing, riding season

For the second year in a row, the Inland Northwest is predicted to face La Niña winter conditions. (Kenleigh Hobby / Courtesy)
By Bill Jennings For The Spokesman-Review

Chances are you will wake up to about an inch of snow on the lawn Saturday morning. Mount Spokane could have as much as a foot or more by then. Is this a signal of La Niña’s promise for a bountiful skiing and riding season? Or just an early tease.

“There’s not a strong signal either way in the Pacific Northwest for above or below average temperature or precipitation until we get deeper into the winter,” said Andy Brown, a meteorologist at the National Weather Service in Spokane.

“Right now we are at a 55-56 percent chance La Niña conditions will develop by the end of the winter,” Brown said. “NOAA is very specific how they define La Niña. Sea surface temperatures in the Pacific have to be at least 0.5 degrees Celsius below normal for three consecutive months. It does take a long time to get to that point.”

La Niña and its counterpart El Niño are phases of the El Niño Southern Oscillation. Also known as ENSO, this refers to a cycle of warming and cooling in the Pacific Ocean.

La Niña begins to develop as Pacific water cools along the coastlines of Ecuador and Peru. This in turn leads to low pressure and enhanced convection over the Indian and Pacific Oceans. This convection pumps moisture and heat into the atmosphere where it circulates north to meet the polar jet stream at about 60 degrees latitude.

La Niña conditions also include a bubble of strong high pressure in the east central Pacific, which deflects the polar jet stream north. This moisture-laden polar jet travels around the bubble and heads south from the Gulf of Alaska along its eastern edge. Next stop is the Pacific Northwest.

La Niña is in the winter outlook for the second consecutive season.

“Last winter we were coming out of a very strong El Niño,” Brown said. “The analogy we used is that if you stretch a rubber band really far one direction, it snaps back pretty far when you let go. Around this time last year we were actually thinking it would be a much stronger La Niña than it ended up being.”

Its degree of influence on our local weather is always unpredictable. Despite brutal cold and ample snowfall, last winter’s La Niña was classified as very weak based on NOAA criteria. Back-to-back La Niñas have occurred five times in the past 70 years. NWS research shows that follow-up La Niñas respond true to form: slightly colder, slightly wetter.

It’s also not a given that a La Niña is necessary for an abundant snow season. Consider the winter of 2008-09, which produced sweet memories for local skiers and riders. In particular it is remembered for 74 inches of snowfall in Spokane from Dec. 17 to Jan 5.

Skiers and riders rejoiced in the mountains while roofs collapsed in town. However, a La Niña didn’t officially exist that winter because the three-month average of sea surface temperatures at least 0.5 degrees Celsius below normal never happened.

Other climate factors have to fall in line before we know more about when this season’s La Niña could arrive, or how productive it could be. According to NOAA’s Climate Prediction Center, a phenomenon called the Madden-Julian Oscillation (MJO) will be a key factor in winter’s outcome. The MJO is a disturbance in pressure and wind that oscillates around the global tropics every 30 to 60 days.

“La Niña gets the most attention,” Brown said, “but the MJO could enhance or suppress the effects of La Niña. Sometimes all the different phases and oscillations work together and sometimes they work against each other. For the time being there are signals that they could work together to bring enhanced precipitation later in the winter.”

La Niña used to be an obscure weather phenomenon known only to meteorologists. Today’s it’s a magic word hyped by the snow sports industry (and columnists) to generate excitement. But it’s always been a pretty safe bet that it will snow in the wintertime around here, sooner or later. Think of La Niña as icing on the cake.