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Avalanche Forecast

Archived

Dec 12th, 2017–Dec 13th, 2017

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

Regions

Northwest Inland.

Treeline and Alpine elevations are wind hammered. The best snow quality for riding can be found on shady, sheltered slopes.

Confidence

Moderate - The weather pattern is stable

Weather Forecast

Wednesday: Mainly cloudy. Alpine temperatures plus 3 degrees with the inversion and freezing levels 800 m. Ridgetop winds light to moderate from the southwest. Thursday: Mix of sun and cloud. Freezing levels 1400 m with a weak alpine temperature inversion. Strong ridgetop winds from the southwest.Friday: Mix of sun and cloud. Alpine temperatures near -4 and freezing levels dropping to 900 m. Strong ridgetop winds from the west.

Avalanche Summary

On Monday, a size 2 slab avalanche was reported. At this point we're not sure if it was skier triggered or a natural. The crown depth was 30-50 cm deep by 30 m wide and ran 150 m. The terrain feature was a steep, wind loaded convex roll above treeline in the "Little Simpson" area.Please submit your information to the Mountain Information Network. Give info get info.

Snowpack Summary

Snow surfaces are highly variable throughout the region. Solar and temperature crusts have formed on sun-exposed slopes, while stiff, stubborn wind slabs linger in lee alpine terrain. Feathery surface hoar and surface facets have formed below treeline up to 1500 m. Approximately 30-50 cm of snow now overlies two crusts that were buried near the end of November. These crusts are widespread and extend into the alpine. Although snowpack tests have previously shown hard results at these crust interfaces, more recent observations have been limited. Below these crusts, a well settled mid-pack overlies the late October crust near the base of the snowpack. This "crust/facet combo" layer is widespread and has been reactive to rider and remote triggers. It also continues to produce a variety of resistant to sudden snowpack test results.Average snowpack depths now total 80-140 cm at treeline elevations and up to 160 cm in the alpine.

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.