Meteorologist has some good news for skiers | AspenTimes.com

Meteorologist has some good news for skiers

Jeremy Heiman

A National Weather Service forecaster has good news for skiers.

According to Mike Baker, a forecaster for the National Weather Service in Boulder, there will be plenty of snow this winter – it just won’t start falling until next month.

Baker says our weather is still under the influence of the La Nia weather phenomenon that was in effect last winter. As a result, the National Weather Service has predicted above-average snow for the northern and central mountains, especially in December, January and February.

This outlook contradicts evaluations by scientists from the Colorado Climate Center and the National Corporation for Atmospheric Research, who have said last winter’s La Nia condition is weakened and on its way out.

“I think our signature for a La Nia winter looks better for this year than last,” Baker said. His prediction is based on observation of ocean temperatures in the tropical Pacific, which have grown colder in recent months.

The Climate Diagnostic Center of the National Weather Service has determined the current La Nia is the 10th strongest in 50 years, Baker said. Climatologists from that office predict the La Nia will start dropping off quickly about March 2000. The present La Nia, a moderate-intensity episode which started in May 1998, has now been in effect for 17 months, Baker said.

One characteristic of a La Nia winter is a northwesterly flow of moisture which is set up by the combination of two jet streams. The polar jet stream provides wind and cold air, and combines with the Pacific jet stream, which adds moisture to the equation.

This combination brings rain and snow to the Pacific Northwest region, and as the air flow continues to the southeast, also brings significant snow to the central Rockies, Baker said. In contrast, El Nio, the weather phenomenon considered La Nia’s opposite, is characterized by a southwesterly flow that consistently brings heavy snows to the San Juan Mountains in southern Colorado.

Moderate to strong La Nia episodes in 1987 and earlier in this decade brought a northwesterly flow to the central Rockies from December through mid-February, Baker said.

But La Nia does not typically bring snow until the end of November or the beginning of December, he said. The extended dry spell that has been putting skiers on edge this fall is actually the norm in La Nia years.

“You’re going to get your snow in the northern and central mountains, but it’s going to start later,” Baker said. The first or second week in December is when the two jet streams typically drop down over Colorado, bringing the cold, wind and moisture.

The outlook for the winter includes cold temperatures and dry powder in December, giving way to warmer times and wetter snows in January and February. A National Weather Service Web site for Colorado weather indicates that strong winds are also a characteristic of La Nia winters.

Baker said he expects a return to what he calls “zonal” air flows, dominated by prevailing westerly winds, in March. This means average temperatures and average precipitation brought by Pacific storms.

The basic condition leading to a La Nia is colder-than-normal water in the central tropical Pacific, and El Nio seems to be dependent on warmer-than-normal water in the same area. Baker said La Nia conditions set up over the world every two to six years.

La Nia and El Nio conditions are in effect about half the time. The rest of the time, with neither phenomenon exerting an influence, western Colorado’s weather is brought more or less at random by northwesterly and southwesterly flows, Baker said.


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