|The 2017-18 avalanche season in Colorado was characterized by a stark north-south gradient in total snowfall, and warm, wet storms punctuating prolonged dry spells. In portions of the Central and Southern Mountains, it was one of the driest winters in the last 40 years. Our Northern Mountains fared better, with some areas quietly sneaking in a decent season with near or even slightly above median annual snowfall. Rain as high as 12,000 feet and several dust events made many us of wonder how winter might look in the future.
There were approximately 2200 avalanches reported to the Colorado Avalanche Information Center (CAIC). CAIC documented 35 incidents, with 45 people caught and three killed – less than the 10-year mean of six fatalities per season. The numbers are likely affected by a shortened snowpack season, particularly in our Southern Mountains, that had long stretches with little avalanche hazard due to poor snow coverage.
An early October storm dropped enough snow at higher elevations to persist through a pronounced fall/early winter drought. A thick foundation of depth hoar developed across much of the state. This layer plagued us for the remainder of the season. We received four “storms” during this drought period with very little snow accumulating prior to Thanksgiving. Each of these storms was followed by extended dry periods of at least a week. Our first close call occurred right after one of these modest loading events on November 18, when a snowboarder near Aspen was caught, carried, and partially buried. Fortunately, he walked away with no major injuries.
The longest period without significant snowfall was from November 18 to just before Christmas. During this five-week dry spell, the snowpack around the state dropped to less than 75% of long-term median, with some areas in the Central and Southern Mountains in the single digits. A “Christmas storm” finally brought snow we could measure in feet. Our snowpack did not handle this test well, and we saw our first, and in hindsight, most widespread avalanche cycle of the season. This pattern – mid to late-month storms interrupting dry periods and leading to avalanche cycles – continued into April. The avalanches in each cycle failed on the facet layer that developed during the early-season drought
The first fatality of the season occurred right after the mid-January storm in the San Juan Mountains near Silverton. Two backcountry skiers were caught and partially buried after venturing into terrain they planned to avoid. One did not survive.
February was the snowiest month of the season for the entire state, accounting for a large percentage of snowfall for the entire season. In some locations in the Southern Mountains, February snowfall amounted to around half of the season’s snowfall. Not surprisingly, we also had a lot of associated avalanche activity, and a little over one third of all avalanche incidents occurred during this one month. The month’s incidents include a solo skier near Berthoud Pass who was caught, carried, and sustained injuries, and a skier near Vail Pass who was partially buried and suffered serious injuries requiring hospitalization.
Mid-February storms produced a remarkably sustained cycle of large and very large avalanches, with D2.5 or larger slides nearly every day for over a week in some locations. The cycle left many professionals searching their memories to recall such a long-lived cycle of avalanches breaking to the ground with very small loads or even just a minor uptick in wind transport.
March was mostly warm and dry. Warm, spring-time temperatures brought a few days of small wet avalanches throughout March, but we didn’t get a pronounced Wet Slab avalanche cycle until later in the season. Storms in the latter half of the month brought rain to 11,000 ft. We had several close calls during the month, but entered April with hopes of finishing the season with only one tragic avalanche fatality.
It was not to be. One of the season’s largest storms arrived on April 6, delivering ample heavy, wet snow over the next three days. Snow-water-equivalent was up to 4 inches of water with 2 to 3 feet of snow in the favored locations. We observed rain close to 12,000 feet at the tail end of the storm. This was an unusual event, and two fatalities occurred in the three-day period right after the storm lifted. On closing day for Aspen Highlands (April 8), a member of the local Search and Rescue group was caught, carried, and killed in the backcountry adjacent to the ski area. An avalanche warning was in effect at the time of accident. On April 10, snowmobilers near Breckenridge triggered an avalanche that broke on the early-season, basal facets. The victim was fully buried and killed. He was wearing a beacon, but it was not turned on. It was sobering to enter the final stretches of the season with two more tragic accidents, each of which has take-home lessons that are too familiar. A number of Wet Slab avalanches followed later in April and into May.
On the education front, the CAIC and Friends of CAIC continued the Know Before You Go program statewide. Combined with our other educational programs, CAIC staff and trained instructors across the state conducted around 150 education events and reached approximately 6300 students. We look forward to improving and expanding these programs for next season.
Lastly – Thank you for your past support and in advance for your continued support. Together we can achieve our strategic goals and continue to build the best avalanche forecast center Colorado has ever seen.