Avalanche Forecast

Archived

Jan 23rd, 2020–Jan 24th, 2020

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, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Rockies.

The MODERATE rating is not intended to be a green light for committing terrain. Natural avalanche activity has largely subsided though human triggered avalanches are still possible.

Confidence

Moderate - Confidence is due to a stable weather pattern; little change is expected for several days. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

Thursday night: Flurries. Moderate to strong southwesterly winds. Freezing level around 1500 m.

Friday: Up to 5 cm new snow. Moderate to strong southwesterly winds. Freezing level around 1500 m.

Saturday: Flurries. Light southwesterly winds. Freezing level around 1500 m.

Avalanche Summary

No new avalanche observations in the previous 3 days. On Monday we received reports of natural and explosive triggered wind slab avalanches size 1.5-2.

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

Snowpack Summary

Recent strong westerly winds have formed stiff wind slabs in exposed terrain at alpine and treeline. A crust can be found at lower elevations and on solar aspects due to recent daytime warming and sun exposure.

A well consolidated mid-snowpack overlies a generally weak basal snowpack. The bottom 10-20 cm of the snowpack consists of facets and deteriorating crusts. There is potential for this deep persistent layer to reawaken in the warm alpine temperatures this week.

Terrain and Travel

Be careful with wind slabs, especially in steep, unsupported and/or convex terrain features.
Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.