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Avalanche Forecast

Archived

Dec 1st, 2021–Dec 2nd, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Rockies.

Watch out for fresh wind slabs forming in the alpine with cooling temperatures overnight. Colder temperatures will help decrease loose wet avalanche activity, but steep slopes will remain a likely place for human triggering.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

Wednesday overnight: 2500m freezing levels will begin to descend, reaching 1800m by morning. Another 10-20mm can be expected, initially falling as rain, and eventually falling as snow at higher elevations. Winds will continue to be strong to extreme from the southwest. 

Thursday: A clearing trend! Up to 15cm of mixed precipitation can be expected in the early morning, with freezing levels sitting around 1700m. Throughout the day, we will see clearing skies, lowering freezing levels, and winds steadily decreasing into the moderate to strong range from the west. 

Friday: High pressure prevails. A mainly sunny day with light winds from the southwest and freezing levels at valley bottom. Another front is on its way in the afternoon, so high clouds may form in the afternoon.

Saturday: Another system is upon us. 10-20cm of snow is expected, with the possibility of locally higher accumulation with upslope enhancement. Freezing levels rising up to 1500m.

Avalanche Summary

There have been very few reports in the past 24 hours. I suspect a widespread natural avalanche cycle has occurred in conjunction with Wednesday's storm. 

Reports from the region remain limited. If you go out in the mountains, please share your observations and/or photos on the Mountain Information Network! 

Snowpack Summary

Heavy rain has soaked the upper snowpack at most elevations. In the high alpine (above 2300m), up to 50cm of wet snow accumulation is possible. Until temperatures cool, this will result in a wet, heavy, and unstable upper snowpack.

Two crusts are found in the snowpack: the mid-November rain crust buried 20-30 cm and reported up to 2100 m, and a crust from early November found at the bottom of the snowpack up to 2300. This crust is beginning to break down and facet. Heavy loading by Wednesday's storm will answer our questions about the potential for failure at this layer.

Snowpack depths range from 40-120cm at treeline elevations. Higher elevations may hold a deeper snowpack, but will also be more heavily impacted by recent winds. Snowpack depths decrease rapidly below 1900 m.

Terrain and Travel

  • The more the snow feels like a slurpy, the more likely loose wet avalanches will become.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.