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Avalanche Forecast

Archived

Feb 2nd, 2021–Feb 3rd, 2021

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

New snow and strong wind from the southwest will build touchy wind slabs in leeward terrain features. Fresh storm slabs may be reactive to rider triggers in sheltered terrain, especially where they sit above a buried surface hoar or crust interface.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Tuesday Night: Snow amounts 5 cm. Ridgetop wind strong from the southwest. Alpine temperatures near -7 and freezing levels at valley bottom.

Wednesday: Mix of sun and cloud. Ridgetop wind 25-40 KM/hr from the West. Alpine temperatures near -6 and freezing levels at valley bottom.

Thursday: Mix of sun and cloud with flurries. Ridgetop wind light to moderate to strong from the West. Alpine temperatures near -10 and freezing levels at valley bottom.

Friday: Light snow up to 10 cm. Alpine temperatures near -26 for the low and -10 for the high. Ridgetop wind generally light with some strong gusts from the West and freezing levels at valley bottom.

Avalanche Summary

No new avalanches were reported on Tuesday. 

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 the forecast snow and strong wind, wind and storm slabs will likley remain reactive on Wednesday.

Snowpack Summary

Up to 10 cm of new snow fell by Tuesday afternoon. The new snow accompanied by a strong southwest 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 may be moist due to rain and higher freezing levels and likely form a crust by Wednesday. This additional snow brings up to 40 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.
  • Pay attention to cornices and give them a wide berth when traveling on or below ridges.
  • Avoid terrain traps where the consequence of any avalanche could be serious.

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.

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.