Put blame on El Niño, expert says

Jim Erickson, Rocky Mountain News

Published October 27, 2006 at midnight

Text size

More Local News

LONGMONT - The storm that dropped up to 20 inches of snow on Colorado's mountains Thursday is typical of the warm, wet autumn snowfalls that hit the state during El Niño years, a University of Colorado climatologist said Thursday.

If history is a guide, the north-central mountains could see more such storms through November, before a drying trend sets in, Klaus Wolter said at the 17th annual South Platte Forum.

"This whole wet fall is consistent with El Niño," he said. "And this warm, wet storm, which pulled in subtropical moisture, is typical."

El Niño is a periodic warming of the tropical Pacific that shifts storm tracks and can affect climate worldwide. The National Oceanic and Atmospheric Administration says weak El Niño conditions now exist and are likely to intensify during the next three or four months.

For years, the conventional wisdom among climatologists was that most El Niño- stoked storms miss Colorado, Wolter said.

But Wolter analyzed 10 El Niño events between 1950 and 1999. He found that El Niño's effects were felt in different parts of the state during different seasons.

Southeastern Colorado's Arkansas River Valley benefits from El Niño moisture year-round, Wolter said. The San Juans, like the north-central mountains, tend to be wet in the fall and dry in the winter during El Niño years.

Along the Front Range, bet on wet during March, April and May. In nine out of the past 10 El Niños, spring was soggy along the Colorado Front Range, Wolter said.

Since 1950, five of the 10 biggest snowstorms in Fort Collins and Boulder occurred during El Niño years. In Denver, it was six out of 10.

Also at Thursday's meeting in Longmont, State Climatologist Nolan Doesken discussed his efforts to determine how much climate warming has occurred in Colorado.

Across the West, spring temperatures have warmed about 2 degrees Fahrenheit during the past 30 years, Wolter said. But in Colorado, the picture isn't as clear-cut as some people seem to think, Doesken said.

"I hear constantly that the climate is obviously changing and it's obviously warmer in Colorado," he said Thursday.

"I haven't been able to reach that conclusion yet," he said. "I'm not seeing that from the data as clearly as other people seem to be."

But there are hints that something unusual is happening. The past 13 Colorado winters have been warmer than average, for example.

That streak is "a big red flag" that tells Doesken "this is beyond the normal (climate) variability that we've observed," he said. Human-caused climate change could be partly to blame, but it's too soon to say for sure, Doesken said.

Last spring, Doesken and Wolter began a trend- analysis project, sorting through weather records from about 200 stations statewide.

Fewer than 20 of the stations had continuous, consistent, long-term records suitable for the study, Doesken said. Data from those stations are being analyzed, and results are expected in mid-November.

Preliminary results show clear wintertime warming signals from the Grand Lake weather station, west of Rocky Mountain National Park, and the Cochetopa Pass station near Gunnison.

At Grand Lake, winter minimum temperatures have increased about 5 degrees Fahrenheit during the past 50 years, Doesken said. At Cochetopa Pass, the winter lows have increased 3 to 4 degrees Fahrenheit during that span.

"Several of the mountain stations, especially mountain valley stations like the Grand Lake example, have been showing this recent and fairly significant warming," he said.

Subscribe to the Rocky Mountain News