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Avalanche Forecast

Archived

Feb 3rd, 2021–Feb 4th, 2021

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

Regions

South Rockies.

Up to 30 cm of recent storm snow accompanied by strong southwest wind has formed reactive slab avalanches. Natural avalanche activity may taper by Thursday but skier and rider triggering remain likely.

Confidence

Moderate - Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack. Uncertainty is due to the limited number of field observations.

Weather Forecast

Thursday: Cloudy with some flurries 3-5 cm. Alpine temperatures near -10 and freezing levels at the valley bottom. Ridgetop winds are strong from the west-northwest.

Friday: Mix of sun and cloud with isolated flurries. Alpine temperature low of -22 with strong ridgetop wind from the West.

Saturday: Mix of sun and cloud. Alpine temperatures low -25 and high -10. Ridgetop wind moderate to strong from the West.

Avalanche Summary

No recent avalanche reports received on Wednesday by 4 pm.  

On Sunday, reports of size 1-1.5 wind slabs were triggered by explosives. Several loose dry avalanches up to size 2 were reported in steep alpine and treeline terrain on the weekend. 

With forecast strong wind, fresh wind slabs, and recent storm slabs will likely remain reactive on Thursday. Loose dry avalanches may occur from steep terrain features.

Snowpack Summary

Up to 30 cm of new snow fell by Wednesday morning. The new snow accompanied by a strong west-northwest wind will likely redistribute some of this snow to leeward slopes and terrain features building fresh storm and wind slabs. The surface snow at lower elevations in the southern part of the region may see a surface crust from the higher freezing levels on Tuesday. This additional snow brings up to 60 cm of storm snow (over the past week) that sits above a plethora of old snow surfaces. In the alpine and at treeline the buried surfaces consist of stiff wind affected snow, surface facets, sastrugi, pockets of soft snow, surface hoar in isolated areas sheltered by the wind, and a sun crust on steep solar aspects. Below 1900 m a thick crust can be found underneath the recent snow. 

A solid mid-pack sits above deeply buried decomposing crust and facet layers near the bottom of the snowpack (80-150 cm deep). Though unreactive under the current conditions, steep rocky slopes and shallow snowpacks should still be carefully assessed and approached with caution.

Terrain and Travel

  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid terrain traps where the consequence of any avalanche could be serious.
  • Be carefull with sluffing in steep terrain, especially above cliffs and terrain traps.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.

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.