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Avalanche Forecast

Archived

Dec 1st, 2020–Dec 2nd, 2020

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

It's expected to be very warm and sunny Wednesday, alpine temperatures could be as warm as +6 C. The snowpack doesn't like rapid changes like this. Cornice failures and even natural avalanches are possible as we head into the warm spell.  

Confidence

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

Weather Forecast

An inversion dominates the forecast period bringing warm sunny conditions to the alpine while the valleys remain cool.

TUESDAY NIGHT: Freezing level at valley bottom with an inversion starting to set up that brings above freezing temperatures between about 2000 and 3500 m, light variable wind, no precipitation expected.

WEDNESDAY: Clear sunny skies, below freezing in the valley with an inversion in place, above freezing temperatures between about 2000 and 3500 m, light variable wind, no precipitation expected.

THURSDAY: Clear sunny skies, below freezing in the valley with an inversion in place, above freezing temperatures between about 2000 and 3500 m, light to moderate west/southwest wind, no precipitation expected.

FRIDAY: Clear sunny skies, no inversion expected, freezing level holding near valley bottom, light variable wind, no precipitation expected.

Avalanche Summary

Warm temperatures and direct sunshine are coming our way. Natural avalanche activity is possible as things start to warm up.

Observations are limited right now, but there have been no reports of recent avalanches. We appreciate the recent reports submitted to the Mountain Information Network. Keep them coming!

Snowpack Summary

Wind slabs have formed on open leeward terrain as last week's 10 to 15 cm of snow was redistributed and formed into more cohesive slabs. Snow surfaces are scoured on windward slopes. 

Surface snow conditions may change with forecast sunshine and warmer temperatures up high this week. Surface snow may be moist and reactive on sunny slopes.

Snowpack depths are variable with reports of 50 to 100 cm in terrain that hasn't been scoured by the wind. There are some reports of a hard crust buried about 30 cm below the surface, which could be a bed surface for wind slab avalanches. The early November crust has been spotted down 65 cm in the region. This layer could become a bigger concern when it gets buried deeper.

Terrain and Travel

  • Be careful as you transition into wind affected terrain.
  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
  • A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.

Problems

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.

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.