Weekly Summary

Avalanche Weekly Summary - December 12, 2024

Posted by: kelsy.been On: 12/12/2024

Northern Mountains

Avalanche activity remained minimal in the Northern Mountains this week, with only two avalanches reported since December 4. The most recent notable event occurred on December 3, when a skier triggered a large avalanche and sustained injuries. A few small storms with strong northwest wind drifted snow onto easterly slopes, burying a weak layer in the upper snowpack. 

Looking across a flat treed area up at avalanche activity in a bowl under a blue skky.
This image shows active wind loading and Wind Slab avalanche activity on an east-facing slope near Berthoud Pass. The field report noted, "On my first lap, only the slide on the left was present, and 50-55 mins later when I made it back up to the top the path on the right had run as well." The most dangerous conditions in the Northern Mountains are slopes with recent wind-drifted snow.

Central Mountains

Following Monday’s storm and Tuesday’s northwesterly winds, observers reported both loose and slab avalanches breaking on a newly buried faceted weak layer in northerly and easterly-facing terrain. A skier was caught and knocked off their feet in a Loose Dry avalanche near Marble on Tuesday. Places that developed the weakest snow surfaces during the early December drought are the easiest places to trigger an avalanche now, including steep wind-sheltered terrain and the bed surfaces of avalanches that released in the Thanksgiving storm.

Southern Mountains

There were only three small human-triggered avalanches reported this week—all in the Northwest San Juan Mountains. These included two Loose Dry avalanches and one small Persistent Slab avalanche. Monday’s storm delivered 6 to 10 inches of snow, and strong winds drifted it onto northerly and easterly slopes above treeline. In areas with less wind, the new snow buried a faceted weak layer in the upper snowpack. 

Heading Into the Weekend

Avalanche conditions have changed since last weekend, with wind-drifted snow and a newly buried weak layer putting Wind Slab avalanches and a new Persistent Slab avalanche problem back on the menu in areas around the state. In addition to the buried weak layer in the bottom half of the snowpack, there's a new weak layer in the upper snowpack, which means many "go to" slopes from last weekend could now be dangerous. Northerly and easterly slopes with hard, drifted slabs of snow will likely accumulate additional snowfall and develop thicker slabs as several small storms move through in the coming week.

annotate image of an avalanche in the Marble area on a stormy day.
Observers reported loose and slab avalanches breaking on the new upper-snowpack weak layer in northerly and easterly-facing terrain in the Central Mountains. This Loose Dry avalanche occurred near Marble on December 10.
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Wind blowing snow at the top of a mountain ridgeline
Monday’s storm and more recent winds changed conditions in the Southern Mountains. In this area, the most dangerous areas are pockets of drifted snow directly below ridgelines and in cross-loaded gullies. 
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