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Avalanche Forecast

Archived

Dec 2nd, 2020–Dec 3rd, 2020

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

Regions

North Columbia.

  

Above freezing temperatures up high over night and into the day Thursday will continue to stress the snowpack. Consecutive hot days are increasing the likelihood of triggering large avalanches on a crust near the bottom of the snowpack.

Confidence

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

Weather Forecast

  

WEDNESDAY NIGHT: Clear / Moderate, southwest ridgetop wind / alpine low temperature +4 / Strong temperature inversion with above freezing air 2000-3500 m.

THURSDAY: Mix of sun and cloud / Moderate, southwest ridgetop wind / alpine high temperature +3 in AM with dropping temps in PM / Strong temperature inversion with above freezing air 2000-3500 m will dissipate in PM.

FRIDAY: Mix of sun and cloud / Light, west ridgetop wind / alpine high temperature -3 / Freezing level 1000 m.

SATURDAY: Sunny / Moderate, southwest ridgetop wind / alpine high temperature +6 / Strong temperature inversion returns with above freezing air 2000-3500 m.

Avalanche Summary

Check out this MIN of a recent human triggered wind slab avalanche at the Gorge.

  

The hot weather up high has the potential to awaken the November crust and make it more sensitive to natural and human triggers which could result in large avalanches.

Data is very sparse in this region. Please submit your observations to the Mountain Information Network!

Snowpack Summary

  

A very strong temperature inversion has created moist snow on all aspects at treeline and above on Wednesday. 10 cm of snow on Monday covered a new layer of surface hoar. 20-40 cm of snow last weekend and strong southerly winds created wind slabs at treeline and above. These wind slabs may remain surprisingly reactive in areas where they are sitting on a layer of small surface hoar. This layer has been described as “spotty” and may only be found in specific areas. A crust from early November exists down approximately 90-130 cm. 

This layer has been observed to have weak, sugary facets above and below it and is most likely to be reactive to human triggers on south facing slopes and in shallow, rocky, snowpack areas in the alpine.

Terrain and Travel

  • Avoid exposure to overhead hazards when solar radiation is strong.
  • Back off slopes as the surface becomes moist or wet with rising temperatures.
  • If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
  • Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.

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.

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.