Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 17th, 2021–Dec 18th, 2021

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

Regions

South Rockies.

Wind will be the main driver of danger today. Seek out wind sheltered terrain where you can avoid wind slabs and find great riding. 

Confidence

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

Weather Forecast

Friday Overnight: Increasing cloud cover into the evening with winds strengthening strong to extreme from the southwest. Temperatures rising steadily reaching -10 C in the alpine by early morning. 

Saturday: A mainly cloudy day with flurries, 2-10 cm of accumulation. Strong to extreme southwest winds, freezing levels rising to around 500m in the afternoon. Continued snowfall overnight with another 5-10 cm of accumulation.

Sunday: Partially cloudy with light flurries, trace accumulation. Wind decreasing into the moderate range from the southwest in the morning and tapering into the afternoon. 

Monday: Mainly clear, cloud cover increasing with isolated flurries in the afternoon. Moderate southwest winds at ridgetop and alpine temperatures around -10 C. 

Avalanche Summary

On Friday, the South Rockies field team was out in the Window mountain area. They observed several natural wind slab avalanches in the alpine up to size 1.5. Read their full report here.

Earlier in the week, operators have reported several large (size 2) explosive-triggered avalanche releasing on the early December crust layer. 

Snowpack Summary

Since Monday, up to 30 cm of snow has accumulated, with another 5-10 cm expected through out the day today. Yesterday, new snow was redistributed by northwest winds into wind slabs in the alpine and treeline. Today, we can expect continued wind slab development as southwest winds redistribute the new snow into fresh wind slabs in the alpine and treeline. 

Below this new snow, more consolidated snow from the previous weekend storm sits over a substantial crust that formed in early December. This crust is likely 20 cm thick (or more) and is present across aspects below 2400m. A thin layer of weak facets (sugary snow) can found above this crust that has demonstrated reactivity in snowpack tests and avalanche activity. 

Snowpack depths vary due to strong to extreme southwest winds from early December that stripped snow off of exposed areas and deposited it onto lee slopes. Below 2300m, several early season crusts are breaking down and forming a cohesive lower snowpack. Snowpack depths range from 60-110 cm at treeline elevations and taper quickly below 1900m.

Terrain and Travel

  • Avoid freshly wind loaded terrain features.
  • Avoid shallow snowpack areas, rock outcroppings and steep convex terrain where triggering is most likely.

Problems

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.