Dashboard Regions Weather Stations Radar Alerts Glossary
Contact About
Log In

Register for an account and never miss a forecast again!

Register

Avalanche Forecast

Archived

Dec 19th, 2019–Dec 20th, 2019

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

Northwest Coastal.

40-70 cm snowfall this week has buried a weak layer of surface hoar. With additional loading from new snow and wind, there is a high likelihood of human triggered avalanches.

Confidence

Moderate - A small change in the upper snowpack could dramatically change avalanche conditions. Uncertainty is due to the complexity of the snowpack’s structure.

Weather Forecast

Thursday Night: Flurries, 5-15 cm. Alpine temperature -4 C. South wind 20-30 km/hr. Freezing level 500 m.

Friday: Snow, 10-15 cm. Alpine temperature -2 C. South-southwest wind 25-45 km/hr. Freezing level 800 m.

Saturday: Snow and flurries, 5-15 cm. Alpine temperature -3 C. Southwest wind 25-45 km/hr. Freezing level 700 m.

Sunday: Flurries, up to 10 cm, Alpine temperature -5 C. Southwest wind 10-30 km/hr.

Avalanche Summary

A natural avalanche cycle to size 2.5 occurred Tuesday, in steep and leeward terrain at treeline and above. In many cases avalanches failed with input from strong to extreme south and westerly winds gusting upwards of 70 km/hr.

Natural storm slab avalanches to size 1.5 were observed around treeline on Wednesday and loose, dry snow was running from steep alpine features. Avalanche control work Wednesday and Thursday triggered numerous large (size 2) avalanches with explosives, crown depths ranged from 30-80 cm. 

As the loose snow gains cohesion and more flurries increase the load on a touchy surface hoar layer, the new snow may be quite reactive to skier triggers.

Snowpack Summary

Heavy snowfall blanketed 40-70 cm snowfall throughout the region this week. The new snow covered a weak layer of surface hoar, old faceted surfaces, and a crust on south/southwest aspects in the alpine. The natural avalanche cycle on Tuesday reported slabs failing at this interface. South-southwesterly winds have developed wind slabs, especially around ridge features and into the alpine.

Reports from the Shames area suggest the surface hoar layer is prevalent on all aspects at treeline elevations down to 800 m, and more likely on leeward and sheltered alpine areas. Ongoing snow and flurries are adding more load and stress to this layer. Check out this MIN report from sheltered terrain near Shames.

The lower snowpack is generally considered strong, as there has been very little to report in terms of recent avalanche activity or snowpack test results on deeper layers. Snowpack depths at treeline range from 100-200 cm and taper quickly at lower elevations.

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.