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Avalanche Forecast

Archived

Feb 1st, 2020–Feb 2nd, 2020

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 unlikely, human triggered possible.
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.

Regions

South Rockies.

Lots of regional variability for Sunday. Elevations that saw only rain on Saturday will trend toward LOW danger with an overnight refreeze. Increased danger will exist in areas where new snow accumulated - especially where it has been redistributed by wind.

Confidence

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

Weather Forecast

Saturday night: Becoming clear with isolated flurries easing into the morning. Strong west winds becoming light by morning.

Sunday: Sunny. Calm or light west winds. Alpine high temperatures around -12.

Monday: Mainly sunny. Calm or light northwest winds. Alpine high temperatures around -13.

Tuesday: A mix of sun and cloud with cloud increasing over the day. Light to moderate southwest winds increasing over the day. Alpine high temperatures around -13.

Avalanche Summary

Reports from Friday showed small (size 1) wind slabs able to be triggered with ski cutting in the Castle area. More intense snowfall and wind throughout Saturday are likely to have spurred a natural avalanche cycle, focused in high elevation, wind-exposed areas.

On Thursday a cornice fall released a size 2 slab avalanche on the slope below on an east aspect at 2150 m. 

On January 16th, a natural, size 2 wind slab stepped down to the deep persistent basal facets below a rock band, details here.

While natural avalanche activity is likely to taper off now that the storm has ended, human-triggering will remain possible at higher elevations where new snow exists and has been exposed to strong or extreme winds.

Snowpack Summary

New snow combined with strong southwesterly winds will continue to build slabs in exposed areas. Cornices have been noted in many areas. A crust can be found up to around 1700 m due to previous warming and sun exposure. 

A well consolidated mid-pack overlies a generally weak basal snowpack. The bottom 10-20 cm of the snowpack consists of facets and deteriorating crusts. While there has been little in the way of avalanche activity on this layer recently, there is potential for it to show up an avalanche reports from the warm wet storm over the weekend. Areas that are most likely to harbor this problem are shallow, rocky start zones. 

Terrain and Travel

  • Be alert to conditions that change with elevation, aspect and exposure to wind.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.

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.