Forecast calls for shades of gray
Winter storms are steadily fattening up local ski slopes. 49 Degrees North will kick off its 2009-10 season Saturday, several weeks earlier than last year. Lookout Pass opened last Friday, a month earlier than it did the year before.
Winter’s early arrival contradicts the return of El Nino that has been bugging some people around here. After back-to-back winters with record snowfall, the thought of anything less has many skiers and snowboarders anticipating deprivation.
After a tantalizing beginning, will skiing and riding for winter 2009-10 be good or bad? Not even the National Weather Service knows for sure.
Every third Thursday of the month, the Climate Prediction Center (CPC) of the National Weather Service releases an updated seasonal weather outlook online at noaa.gov. Yesterday’s report said moderate El Nino conditions that emerged last summer might be at maximum strength.
El Nino refers to above-normal temperatures in the waters of the equatorial Pacific. La Nina, the engine for record-breaking winters, cools those waters. The La Nina/El Nino cycle changes about every one or two years. A complete cycle takes from three to seven years.
The presence of El Nino leads the CPC to predict that temperatures will be above normal and precipitation will be below normal in the Pacific Northwest through December, January and February.
But the forecast isn’t all doom and gloom, according to John Livingston, meteorologist in charge at the National Weather Service in Spokane.
“It’s not a dire forecast,” he said. “The main thing that we talk about with El Nino is warmer temperatures. It’s not forecast to be exceedingly warm, just a shift toward warmer temperatures and higher snow levels.”
Livingston said there is no clear signal that ties El Nino with an increase or decrease in precipitation. But with higher snow levels, snowstorms probably won’t clobber the city as they did last year.
El Nino will affect the jet stream, however. There are two jet streams across the Pacific Ocean. The polar jet powers Pacific Northwest storms. The tropical jet flows across Mexico. In neutral conditions, the polar jet points right at the Northwest in fall and winter.
The warming effect of El Nino is expected to send the polar jet up and over the Northwest. But even though chances of warmer temperatures are predicted, Livingston said we should still expect winter’s wrath.
“The tough part about explaining El Nino is that we’re talking about seasonal impacts,” he said. “There’s a chance that El Nino will make temperatures warmer than average over a three- to six-month period, but it doesn’t rule out the fact that we could have the worst Arctic outbreak in years.”
Livingston said long-range forecasting is pretty vague. Outlook scenarios are painted over large areas for extended periods of time. Specific predictions aren’t possible. As an example, he referred to the 90-day precipitation outlook over the Inland Northwest.
A chance of below-normal precipitation was pegged at 40 percent, above-normal precipitation at 27 percent and an equal chance of above or below normal at 33 percent.
“It’s an inexact science at best,” Livingston said. “There are a lot of shades of gray. When you dig in to examine the relationship between what is being forecast and what is normal, a bunch of different scenarios could happen.”
After back-to-back winters with big snow totals, the odds are against chances of a third. The last time three winters in a row were above average in Spokane occurred from late 1949 to early 1952.
“There’s a lot of variability in weather that’s not explained by the El Nino/La Nina cycle,” Livingston said. “The chance of having big winters back to back to back is slim, but it’s a never-say-never situation.”
Bill Jennings can be reached at firstname.lastname@example.org