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Avalanche Forecast

Archived

Jan 21st, 2020–Jan 22nd, 2020

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

Use extra caution in avalanche terrain when air temperatures rise above zero, especially for the first time. Also be alert to slopes getting direct sun, if it comes out Wednesday. These two factors can make slabs more sensitive to triggering.

Confidence

Moderate - Uncertainty is due to difficult to forecast freezing levels.

Weather Forecast

The freezing level spikes over the next few days will be more pronounced the farther south you go in the region.

Tuesday night: Overcast with isolated flurries bringing up to 5 cm of new snow. Moderate southwest winds. Alpine low -6 C. Freezing level dropping to around 1000 m.

Wednesday: Broken cloud with isolated flurries bringing a trace of new snow. Moderate west to southwest winds. Alpine high -5 C. Freezing level around 1300 m.

Thursday: Mix of sun and cloud with isolated flurries bringing a trace of new snow. Moderate west to southwest winds. Alpine high -1 C. Freezing level rising to 1800 m.

Friday: Mix of sun and cloud with isolated flurries bringing a trace of new snow. Moderate west to southwest winds. Alpine high +1 C. Freezing level around 2000 m.

Avalanche Summary

On Monday we received reports of natural and explosive triggered windslab avalanches size 1.5-2.

On Thursday 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 windslabs low in alpine lees. 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 later in the week.

Terrain and Travel

  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • Minimize exposure to sun-exposed slopes when the solar radiation is strong.
  • 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.