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Mountains make mysterious weather

Tom Wiesen

I think it is fascinating to observe mountain weather because it is so variable.

Have you ever noticed how some areas are piled deep with snow, while other areas have melted or blown dry? What factors affect this distribution of snow? Analyzing the lay of the land helps us understand why it snows here in the first place.

To the west of Colorado lay vast arid lands. Relatively warm air moves in from the west and runs into the high mountains. The warm air is forced up and rapidly cools which results in condensation. Cold air is less capable of holding moisture than warm air and rain or snow soon falls from the sky.



The western slopes of the mountains receive the bulk of the moisture from passing storms. As storms move over the highest ranges, a precipitation shadow forms to the east of these land masses and the climate is super-dry.

For instance, right now you could hike to the summit of 14,000-foot-plus Mount Princeton with just boots and gaiters. Eastern slope mountains are much drier, and are often windy and consequently hold little snow.

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Meanwhile the snow at 10,600-foot Vail Pass is over 6 feet deep. What causes this concentration of snow? In Colorado, as the weather comes from the west, not only is it forced up rapidly by the mountains, but it is also funneled up major river valleys that run east to west.

Major rivers such as the Eagle, Roaring Fork, Yampa and San Juan all concentrate weather systems and then stall them as they reach the heads of these valleys where high mountains jut up. The faster the weather is forced up, the more dramatic the affect on precipitation.

Dreamy backcountry lines



Eagle County is blessed with two major mountain ranges on either side of the Eagle River that funnel our weather. The Gore Range borders the north with sharp and dramatic peaks rising above 13,000 feet.

Meanwhile the lofty Sawatch Range runs east-west along the southern edge of Eagle County eventually rising above 14,000 feet, boasting the highest peaks in the state in neighboring Lake County.

Snow depth typically increases as the elevation gets higher. However, once above tree line strong winds often scour the slopes and deposit snow in the leeward areas. This is why you can look up at high peaks and notice that some areas are bare rock while other areas form dreamy lines for backcountry skiers.

You may also notice that some areas melt completely during sunny periods without snow. These south-facing slopes often hold shrubby plants where wildlife such as elk, bighorn sheep and mule deer thrive.

Meanwhile just across the valley on the shadier, north-facing slope ” such as the front of Vail Mountain ” the snow may be over four feet deep. This is an example of a local microclimate.

Sunny slopes are far warmer than shady slopes and oftentimes a sun-crust will form on the sunny snow surfaces, while neighboring areas remain dry and powdery in the shade. Experienced skiers head for the shaded areas to find soft powder after days of sunshine.

Dominating pines

Now consider the notion of a precipitation shadow. Examples of this are evident on the eastern side of the Sierra Nevada, on the eastern side of the Cascades, and to the east of the Rockies.

Storms drop the bulk of their moisture, lose momentum and break up after they pass over the highest areas. While ski areas on the Western Slope start at around 8,000 feet elevation, east slope ski areas must be higher if they’re to have ample snow.

Also consider how precipitation affects plants. In arid moderate elevations junipers, pinon and sagebrush thrive. As elevation increases and precipitation increases, we get Douglas firs and aspens. At the highest and wettest elevations, thick subalpine forests are dominated by lodgepole pine, Engelmann spruce and subalpine fir.

Trees hardly found on the Western Slope can thrive on the Front Range.

For instance, high-and-dry, windy ridges often support limber and bristlecone pine. But below 10,500 feet on the East Slope, ponderosa pine often dominates. These trees require a dry climate and do not form a thick forest with a closed canopy. Ponderosa pines are more spread out, forming woodlands.

Mountain weather is complex and mysterious at times. While our region has been hammered with consistent snow, other areas in the state remain dry. Deep snow benefits skiers, whitewater enthusiasts, farmers and ranchers. We should be thankful that this season’s weather pattern has favored us.

Tom Wiesen and his wife Tanya are the owners and lead guides of Trailwise Guides, a year-round Vail Valley guide service specializing in providing quality experiences. Private snowshoeing, cross-country skiing and wildlife-watching outings are offered daily. Contact Trailwise Guides at 827-5363.


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