Chugach State Park

Recent Avalanches:  Over the past week, several avalanches were observed. In the South Fork of Eagle River, two large natural avalanches were observed on Swiss Bowl and Italian Bowl on NNW aspects. Their slide paths ran ~1,000ft. The start zones were at elevations between 3,700’ and 4,000’, The slides appeared to be triggered naturally from cornice falls during the major wind events around Christmas. They were reported to have likely failed on the faceted layer at the base of the snowpack. Other smaller avalanches were observed in that area on NNW aspects with start zones in the same elevation bands as the larger avalanches. The smaller avalanches appeared to have failed midway through the snowpack and appeared to be triggered naturally from cornice falls. Lastly, three hikers and one skier triggered avalanches on Flattop. The hikers triggered a slide on the NW face of Flattop directly south of Blueberry Knoll. The skier triggered a slide on the main Flattop gully. Everyone was okay.

Weather Recap: In the past week, the Front Range has received roughly 11” of new snow with moderate to strong winds at ridgetops predominately from the north and east. The Arctic Valley weather station recorded gusts up to 60 mph on December 23rd at 8:00 am. Temperatures ranged from -16F (in the valley of the South Fork of Eagle River) to 27F (Arctic Valley Weather Station) with an average of around 8F.

Weather Forecast: Starting tonight (Dec 29th) we are looking at mostly clear skies with colder temps in the single digits (dipping as low as -3F). The cold and clear weather is looking like it will stay until Saturday afternoon. Starting Saturday afternoon, winds are forecast to increase and blow in the 20-40mph range by Saturday night through Sunday. Only 1-2” of snowfall is expected this weekend, with light precipitation starting Saturday afternoon and continuing through Sunday evening. Temperatures should rise from -3F to the teens F during the day Saturday and then continue to rise to the twenties Sunday afternoon and evening.

The overall snow depth is highly variable in the Front Range right now. In many areas, the wind has scoured the landscape leaving bare ground exposed. The snow has been deposited in other areas that tend to fill up with snow, like gullies and alpine bowls. The snowpack is deep in these locations and is potentially harboring buried weak layers.

Wind-scoured view of The Front Range in the Glen Alps Recreational Area. Photo by Andy Kubic on 12.26.23

Photo of Death Bowls taken on 12.28.23

Both lingering wind slabs from the high wind events around Christmas and new wind slabs that might develop for Sunday should be on our minds. Several skier-triggered wind slabs were observed this past week as well as reactive snow test results roughly 6” down from the snow surface on the interface between a layer of near surface facets and wind slab in the South Fork of Eagle River. To identify areas with wind slabs look for active wind transport and feel for firmer, stiffer snow on the surface, and cracks in the snow that shoot out from you. Using small test slopes can be a good way to check whether wind slabs are reactive to human triggers in the area you are traveling. Wind slabs can be avoided by sticking to sheltered or wind-scoured areas. Keep in mind, given the weak snow layers buried deeper in the snowpack (Problem 2), a relatively small wind slab triggered near the surface has the potential to step down to a deeper weak layer.

Wind-scoured and wind-deposited landscape in Glen Alps Recreation Area. Photos taken on 12.26.23

There are three layers we are watching within the snowpack. The most concerning layer is the facets at the base of the snowpack at higher elevations. In the South Fork of Eagle River, two larger avalanches were observed on Swiss Bowl and Italian Bowl on NNW aspects that are thought to have failed on this layer. The other layer is a thin layer of facets about 20” deep which exists right above the Thanksgiving crust. This has been observed at lower elevations. Lastly, the interface between near surface facets and wind slabs ~6” down from the snow surface in the snowpack has gotten reactive test results this past week. The best way to manage persistent slab problems is to stick to lower-angle terrain.

The facet layer that likely failed at the base of the snowpack Swiss Bowl and Italian Bowl start zones 12.28.23

Thanksgiving crust spotted in snowpack at base of False Peak snowpit on 12.26.23