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

Jan 21st, 2020–Jan 22nd, 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 and human triggered avalanches likely.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches possible, human triggered probable.
Alpine
Natural and human triggered avalanches likely.
Treeline
Natural and human triggered avalanches likely.
Below Treeline
Natural avalanches possible, human triggered probable.

Regions

Northwest Coastal.

Southerly winds are forecast to build over the day Wednesday, forming touchy windslabs from recent storm snow.

Confidence

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

Weather Forecast

Tuesday night: Overcast with isolated flurries bringing a trace of new snow. Light wind from the southwest. Alpine low -2 C. Freezing level around 800 m.

Wednesday: Overcast with isolated flurries bringing up to 5 cm of new snow. Winds building to strong south through the day. Alpine high -1 C. Freezing level around 1000 m.

Thursday: Heavy snowfall bringing 20-40 cm of snow with rain below 500 m, concentrated in the south of the region. Strong southwest winds, approaching extreme at ridgetop. Alpine high -3 C. Freezing level around 1000 m.

Friday: Heavy snowfall bringing 20-40 cm of new snow with rain below 500m, concentrated in the south of the region. Strong southwest winds. Alpine high -1 C. Freezing level around 1000 m.

Avalanche Summary

A widespread natural storm slab avalanche cycle up to size 3 was observed as the storm tapered off Monday. Reports of artificially triggered storm slab avalanches include remote size 1.5-2.5 near treeline. Explosive control work below treeline in the highway corridor produced results up to size 1.5.

Reports of deep persistent slab avalanches have been trickling in throughout the month. They are associated with a November crust layer near the base of the snowpack which has produced very large avalanches (size 3+) with crown depths of around 2 m. Observations are typically in alpine terrain, on lee or cross-loaded slopes. 

Snowpack Summary

60-90 cm of recent snow is forming fresh windslabs as southerly winds build through the day Wednesday.

The new snow rests on extensively wind affected surfaces at upper elevations, and a thick layer of weak facets in sheltered areas treeline and below.

A deep crust from mid November lurks at the base of the snowpack. A few recent large avalanches have run on this layer on lee and cross-loaded features high in the alpine. This week's succession of storms adding significant new load to the snowpack will be a good test of this layer.

Terrain and Travel

  • Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
  • Fresh wind slabs will likely form throughout the day, diligently watch for changing conditions.
  • Wind slabs are most reactive during their formation.
  • Be aware of the potential for large avalanches due to the presence of a deep persistent slab.

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.