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Avalanche Forecast

Archived

Jan 31st, 2020–Feb 1st, 2020

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

Regions

Sea To Sky.

Avoid avalanche terrain Saturday. The snowpack will take time to adjust to significant new loading from snowfall, extreme wind and rain.

Confidence

High -

Weather Forecast

Friday night: 40-70 cm new snow in the alpine with rain below 1500 m. Extreme southwest wind. Freezing level 1700 m.

Saturday: 10-15 cm new snow in the alpine, with rain below 1300 m turning to snow as freezing levels drop. West wind easing from strong to moderate. Freezing level 1500 m dropping to 500 m through the day.

Sunday: Mix of sun and cloud with flurries bringing 10-15 cm new snow. Moderate southwest wind. Alpine high -6 C. Freezing level 300 m.

Monday: Sunny. Light north wind. Alpine high -6 C. Freezing level valley bottom.

Avalanche Summary

Natural loose wet avalanches running on the January 20 crust were observed up to 1900 m on Friday. Storm slabs up to size 2 were reactive to explosive and skier control work 1900-2000 m. Alpine observations have largely been obscured by poor visibility through the storm but a widespread avalanche cycle is expected to be ongoing through Saturday.

The deep persistent problem most recently reared its head on Monday with large explosive loads producing a size 2.5. in shallow, rocky terrain. There is potential for the new snow loads to induce failures on these layers resulting in very large and destructive avalanches. 

Snowpack Summary

By Saturday morning, storm totals are forecast to reach 80-100 cm with another 10-15 cm falling though the day. Forecast extreme winds and strong temperatures will speed up slab formation as new snow accumulates as well as contribute to rapid cornice growth. At lower elevations new snow will overly a crust from the preceding rain as freezing levels drop through the day. 

Weak faceted grains and crusts near the base of the snowpack continue to be a concern in inland parts of the region such as the Spearhead Range. Loading from new snow and rain will further stress these buried weak layers where they exist.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

Problems

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.

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.