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 19th, 2021–Dec 20th, 2021

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

 Human triggered wind slabs remain likely as strong winds are expected to form fresh slabs throughout the day. 

A buried persistent weak layer continues to warrant careful terrain selection and diligent decision making.

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

Sunday Overnight: Light northerly winds and partially cloudy skies. Temperatures dropping to -16 C in the alpine. 

Monday: Mainly cloudy with a chance of flurries. Alpine temperatures around -10 C. Strong southwest winds at ridgetop.  

Tuesday: A mix of sun and cloud. Strong southwest winds at ridgetop, reaching extreme in the afternoon. Temperatures rising with an alpine high of -7 C. Cloud cover increasing into the evening.

Wednesday: Cloudy and snowing, 3-15 cm accumulation. Strong to extreme southwest winds at ridgetop. Alpine temperatures around -8 C.

Avalanche Summary

On Sunday, operators reported isolated size 1 wind slabs with explosive control. They reported whoomphing in previously unskied/uncontrolled terrain.

On Saturday, operators observed cracking, whoomphing, and skier triggered wind slabs up to size 1.

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.

Snowpack Summary

Saturday's 10-20cm of storm snow was redistributed by moderate to strong winds into wind slabs in the alpine and treeline. This new snow overlies a variety of wind effected surfaces formed by strong to extreme winds, stripping many areas in the alpine and exposed treeline and creating hard wind slab in others.

Below this, a layer of more consolidated snow sits over a substantial crust that formed in early December. This crust is up to 20cm thick and is present across all aspects below 2400m. Up to 10cm of faceting has been reported above this crust. This problem is particularly hard to predict and tricky to manage. For this reason wide, conservative terrain margins and disciplined backcountry travel techniques will be very important. Get more details and photos in our forecaster blog. 

Snowpack depths vary due to strong to extreme southwest winds that stripped snow off of exposed areas and deposited it onto lee slopes. Below 2300m, several early season crusts make up the lower snowpack. Snowpack depths range from 60-100 cm at treeline elevations and taper quickly below 1900m.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
  • 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.