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Richard Nauman and his son Tomas, 3, drove from Talent to check out the first several inches of snow to fall on Mount Ashland. Bob Pennell / Mail Tribune photo - Mail Tribune / Bob Pennell

La Niña suggests cooler, wetter weather

The soggy weekend that set a record for rainfall on Sunday may be a precursor of things to come. Or not.

The storm broke the record for rainfall on Oct. 24, dumping 1.11 inches on the Medford area and exceeding the previous record set on Oct. 24, 1940, of .89 inches, according to the National Weather Service.

Above average rainfall is expected to continue through October and November in Southern Oregon, driven by a looming La Niña system that will blow weather moisture and cold air off the ocean from the west and northwest, said Shad Keene, a National Weather Service climatologist in Medford.

The weekend's storm dropped the first sticking snow in the mountains for the season but arrived too early to be considered part of the La Niña pattern, which is likely — but not certain — to bring a cooler, wetter winter and more snow for December through February, says Keene.

Predictions of a La Niña-driven hard winter have come from several sources, including the federal Climate Prediction Center, the branch of the National Weather Service that monitors short-term climate fluctuations.

But La Niña is tricky to predict, says Ryan Sandler, a warning control meteorologist with the weather service, nothing that the systems often bring dry weather to Southern California and wet weather to Northern California and the Northwest. The Rogue Valley is close to the "switchover" point between the wet and dry areas, so the possibility remains that the wet weather will veer farther north.

La Niña systems of the last dozen years often brought heavy snowfall on the ground in Medford, 9 and 10 inches in two of the bigger years for the valley floor. But one La Niña pattern produced only 1 inch of snow at the airport. The average is 3.5 inches of snow for all years.

This weekend's storm does not signal an early winter, Sandler said.

"We had above-average temperatures for a long time and now we've moved on from summer and are getting some below-average temperatures," he said.

During the record-setting rain Sunday, temperatures in the Medford area were 8 degrees below normal, he added.

The weather service website says that, during the storm Saturday and Sunday, rainfall totaled 1.45 inches at the Medford airport, with 1.94 inches on Evans Creek. For the two days in Josephine County, rainfall totals were as much as 4.92 inches while Curry County recorded 5.43 inches in one spot.

While rumors of a bad winter are quick to spread, you can only say with certainty that most heavy rainfall years do occur during La Niña periods — and years of light rain and warmth tend to occur, as last winter, with El Niño periods.

El Niño patterns accompany the warming of sea surface water off Central America, while La Niña comes from the cooling of those waters. La Niña comes in cycles of three to five years. Such shifts affect the jet stream and Southern Oregon's weather, says Keene, with El Niño blowing in weather from the south and La Niña pushing it in from the west and northwest.

"One La Niña season can be dry, normal or wet, but most are wet," says Sandler. "No one can guarantee that one particular La Niña will be wet.

Since most La Niña episodes are wet, does that mean increased chance of flooding?

"They tend to have more rain and flooding, but you can't bet on it for this or any one year," he notes. "If you had the money to bet for every year, you would win, but if you bet on one year, you could lose it all."

John Darling is a freelance writer living in Ashland. E-mail him at jdarling@jeffnet.org.

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