Summit County Citizens Voice

Colder than average sea surface temps shown in blue indicate the La Niña pattern that has already brought some record low winter temperatures to parts of South America, while dark orange shows how the warmer than average water has sloshed westward all the way to Indonesia.

December, January tabbed as snowiest months during a presentation to the Colorado Snow and Avalanche Workshop

By Bob Berwyn

SUMMIT COUNTY — Predicting the weather more than a few days in advance involves equal parts skill, art, science and luck, especially in Colorado, which sits in something of a meteorological no-man’s land.

But Joe Ramey, a climatologist with the National Weather Service in Grand Junction, went out on a limb last weekend to forecast a snowy winter, beginning in December and lasting at least through January, and possibly into February.  The early part of the ski season might stay dry and warm a little longer than most eager skiers and snowboarders would like, but odds are the dumps should arrive for the heart of the season, he said.

“The weather flip-flop in 2010 gives us a high level of confidence … but don’t bet the ranch,” Ramey said, speaking last week at the annual Colorado Snow and Avalanche Workshop in Leadville.

He based his forecast on the dramatic shift away from El Niño to La Niña, with much cooler than average sea surface temperatures in the eastern equatorial Pacific. Based on those temperature readings, this year’s La Niña is shaping up to be one of the strongest in several decades, but that alone doesn’t guarantee a big winter.

In general, those ocean temperature fluctuations help determine the track of the jet stream, the strong upper-level winds that push weather systems from west to east. In  La Niña years, that pattern tends to bring the heaviest precipitation to the Pacific Northwest, while often leaving Southern California and the Southwest dry. After driving into Washington and Oregon out of the Gulf of Alaska, the storms traveling along the jet stream often have enough moisture left over for good snowfall over the northwestern corner of Colorado.

Another plus for our area (if you like snow, that is): The local mountains are oriented in a way that enhances snowfall through orographic lifting. As the moist stream of air passes through our area, it’s forced upward by the mountains, triggering condensation and precipitation. Even without a well-defined low pressure system, a steady, moisture-laden flow from the northwest can bring steady light to moderate snowfall that gradually adds up to impressive amounts.

Ramey makes his seasonal predictions by looking at historic snowfall records at a scattering of weather stations around the state. He compares that data with the large-scale variations like the El Niño to La Niña cycle, as well as lesser-known variables like the Pacific Decadal Oscillation.

http://www.atmos.washington.edu/~mantua/REPORTS/PDO/PDO_egec.htm

Based on those observations, Ramey said he couldn’t find any dry years matching with  La Niña conditions. Looking at the average of his six study sites, Ramey said the record shows there is good chance for enhanced precipitation in December and January.

“I think we can expect enhanced snowfall from December through January, and maybe February, and perhaps a drier than normal fall and spring … We have pretty high confidence in this seasonal seasonal outlook,” he said.

Looking back at some other strong Strong La Niña years, Ramey said the winter of 1998 -1999 was dry overall, with a very stormy January. In 1999-2000, good snows fell in December and January, with average or just-below average precipitation the rest of the winter, while 2007-2008 brought above-average snowfall from December all the way through May.

“There aren’t any La Niña years showing up in the record of driest years … this winter, I think, looks pretty good,” he concluded.

Filed under: climate and weather, Environment, La Niña, Summit County Colorado, Summit County snow and weather Tagged: | Colorado winter snowfall predictions, La Niña 2010, Pacific Decadal Oscillation, ski season outlook 2010, Summit County Colorado, Summit County News, Summit County snow 2010, weather