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Avalanche Forecast

Archived

Jan 22nd, 2022–Jan 23rd, 2022

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

Sea To Sky.

Major warming and sun are expected to destabilize the snowpack over the weekend. Wind slabs are expected to remain reactive, cornices will continue to weaken, and deep weak layers may begin to wake up. Wet loose activity should be expected on steep sun exposed slopes.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

The region now sits under the warm ridge of high pressure which is expected to persist into next week bringing very high freezing levels and sun. 

Saturday night: Partly cloudy, light W wind, freezing level 2800 m with an inversion.

Sunday: A mix of sun and cloud, light W wind, freezing levels around 2500 m with an inversion, dropping to around 2200 m by Sunday night. 

Monday: Sunny, light NW wind, freezing levels around 2700 m with an inversion. 

Tuesday: A mix of sun and cloud, light NW wind, freezing levels around 2700 m with an inversion. 

Avalanche Summary

On Friday, natural and skier triggered wind slabs size 1.5-2 were observed and explosive control work produced size 2 cornices. Small solar triggered loose wet avalanches were observed on steep south facing terrain. On Thursday, a few natural wet loose avalanches size 1-2 were observed at treeline and below during the storm as well as some small loose dry at higher elevations. Ski cutting triggered a couple storm slabs size 1-1.5 and explosives triggered several size 2 storm slabs and cornices. The storm slabs appear to typically be 20-30 cm thick but up to 50 cm in loaded terrain.

Last week, a very large natural avalanche cycle took out mature timber and left mountainous piles of debris down to very low elevations. Check out the insane photos of the size 4 in this MIN from January 15th. Avalanches of this scale wouldn't be surprising during the current warm weather. Parts of the region are currently under a Special Public Avalanche Warning (SPAW). Check out this new blog post for additional information. 

Snowpack Summary

At higher elevations, 15-30 cm of recent storm snow has buried the widespread January 16 melt-freeze crust which extends to around 2100 m. There have also been some observations of surface hoar sitting on the crust on polar aspects at treeline and in the alpine north of Pemberton but this does not appear to be widespread. The most recent storm snow has formed reactive wind slabs in exposed high elevation terrain. At lower elevations, the upper snowpack is moist or wet from the recent rain event. 

The depth of the early December crust/facet layer is highly variable through the region but appears to be typically down 100-200 cm. Some operators are showing the depth as low as 60 cm in shallow snowpack areas and as deep as 3 m in wind loaded terrain. The weak layer is most prominent between 1700 and 2100 m. The layer has been dormant recently but is a concern for the period of major warming and sun forecast over the weekend. The most likely place to trigger it would be in thin, rocky snowpack areas where it is shallowest. 

Terrain and Travel

  • The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
  • The more the snow feels like a slurpy, the more likely loose wet avalanches will become.
  • Cornices become weak with daytime heating or solar exposure.
  • Avoid exposure to overhead avalanche terrain as temperatures increase.
  • Be aware of the potential for large, deep avalanches to run full path or even longer.

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.

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.

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.