The temperature in Minneapolis didn’t fall to zero degrees this winter until Jan. 12. On Jan. 5, the daytime high in Rapid City, S.D. (a record-setting 71 degrees) was higher than in balmy Miami (69 degrees). And just a couple of days before New Year’s, visitors to Park City, Utah, skied on man-made snow and dined al fresco — without their parkas.
Throughout the continental United States, it’s been a very warm winter.
“The talk across the whole country has been, ‘Where has winter been?’ ” said Dale Eck, who runs the global forecast center at the Weather Channel in Atlanta.
The answer: A combination of factors has trapped the winter’s cold air in the northern latitudes over Canada and Alaska.
Sunshine and nearly 80-degree temperatures in downtown Los Angeles this week — combined with an early January heat wave and vicious Santa Ana winds in late November and early December — might leave locals with the impression that winter has been similarly balmy in Southern California.
But while the season is shaping up to be exceptionally dry, it has not been unusually warm.
In fact, November’s average high temperature of 69 degrees in downtown Los Angeles was four degrees below normal, and December’s average of 66 was two degrees below normal, said Ryan Kittell, a forecaster at the National Weather Service’s Oxnard, Calif., office.
In January, however, there have been an unusual number of days when the temperature downtown exceeded 80 degrees — four, as of Friday. January usually has two such days, on average. Those days have pushed the average temperature for the month so far to 70 degrees, which is two degrees above normal.
“If you look at U.S. temperatures, you’d say, ‘Wow, it was a warm winter,’ ” said Dan Cayan, a climate researcher at the U.S. Geological Service and the Scripps Institution of Oceanography in La Jolla, Calif. And you’d be right.
“But,” he added, “in the coastal West, it’s been cool.”
Scientists said the cyclical cooling in the Pacific Ocean known as La Nina was a likely cause for dry conditions in California and across the nation.
There’s an 82 percent probability of less-than-normal rainfall in a La Nina year, said Bill Patzert, a climate researcher at the Jet Propulsion Laboratory in La Canada Flintridge, Calif.
Cayan chalked up the cool temperatures on the West Coast to its position on the eastern edge of a La Nina-related high pressure center over the Pacific Ocean that has created a dry, cool air flow in the region.
La Nina has also helped keep the jet stream on a west-to-east path over Canada, preventing cold Arctic air from dipping into the Lower 48 states, he said.
A phenomenon known as the Arctic oscillation has reinforced that effect, Patzert said.
The oscillation is a pattern of pressure that wraps itself around the North Pole. When the pressure is low, as it has been for most of this winter, the oscillation captures the cool air that normally breaks out of the Arctic and moves into Canada.
The Arctic Oscillation shifted in January, leading some meteorologists to predict that cold air would soon dip farther south, allowing the winter to finally begin in earnest.
But since La Nina can persist for years, Cayan said he suspected it was unlikely California would catch up on rain and snowfall this year.
“We’re so far behind right now,” he said.
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