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Avalanche Forecast

Archived

Dec 2nd, 2020–Dec 3rd, 2020

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, 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 Alpine heat wave continues! Above freezing alpine temperatures (+5 C) & sunny skies will persist on Thursday, increasing avalanche hazard. Cornice failures, loose wet avalanches & slab avalanches are likely with this heat. Choose your terrain wisely to limit exposure.

Confidence

Low -

Weather Forecast

A temperature inversion dominates the forecast period bringing warm sunny conditions to the alpine while the valleys remain cooler.

WEDNESDAY NIGHT: Clear skies and a temperature inversion between~1800m and 3500m are forecast to persist overnight. Below the inversion, fog and below freezing temperatures are forecast for the valleys. Winds will be light & variable with no notable precipitation expected.

THURSDAY: A temperature inversion persists during the day with clear sunny skies and above freezing temperatures (up to +6C) 1800m - 3500m, with valley fog and below freezing temperatures in valleys. Winds will be light to moderate west/southwest & no precipitation is expected. The inversion is replaced by cooler air overnight and freezing levels will drop to valley bottom.

FRIDAY: A mix of sun and clouds, with a second inversion building in the afternoon, freezing levels rising to 3500m, moderate to strong South-Westerly wind, & no precipitation expected.

SATURDAY: Above freezing temperatures strengthen in the Alpine, light-moderate West/Northwesterly winds, no precipitation expected.

Avalanche Summary

Above freezing Alpine temperatures (+5 to +10C) were reported on Wednesday and are forecast to persist through Thursday. Pinwheeling and loose snow avalanches were reported in adjacent forecasting regions Wednesday. Natural avalanche activity is anticipated with this warming. 

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

Snowpack Summary

Surface snow conditions will change with forecast sunshine and above freezing temperatures in the alpine this week. Surface snow may be moist and reactive on sunny slopes, creating crusts when re-frozen.

Wind slabs formed on open leeward terrain when last week's 10 to 15 cm of snow was redistributed and formed into more cohesive slabs. Snow surfaces are scoured on windward 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.
  • 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.
  • Extra caution for areas experiencing rapidly warming temperatures for the first time.

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.