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 20th, 2020–Dec 21st, 2020

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

Give the snowpack time to adjust to recent loading, especially in open areas where snow may have been wind stiffened. Use small low consequence slopes to test the bond of the recent snow to older layers.

Confidence

Moderate - Uncertainty is due to limitations in the field data.

Weather Forecast

SUNDAY NIGHT - Flurries, 5-10 cm / light southwest wind gusting to strong / alpine low temperature near -3 / freezing level down to 300 m

MONDAY - Cloudy with sunny periods and isolated flurries 0-5 cm / light to moderate north west wind / alpine high temperature near -4 

TUESDAY - Cloudy with sunny breaks, no new precipitation / light winds / alpine high -4 

WEDNESDAY- Flurries, moderate accumulations possible, light gusting to moderate winds, inversion possible

Avalanche Summary

On Sunday there were reports of shooting cracks in convex (roll over) type features. Avalanches up to size 2 out of steep, wind loaded features were reported on Saturday.

On Wednesday and Thursday there were many MIN reports suggesting the ever increasing storm snow amounts were reactive to human triggering.

Please consider sharing your observations with the Mountain Information Network; even just a photo of your day helps. Thank you to those that have already submitted this winter!

Snowpack Summary

Precipitation will start to ease by Monday but storm slabs may continue to reactive to human triggering especially where the snow has been stiffened by wind. Some areas have seen upwards of a meter of new snow in the past week.

A crust that was buried in early December is now down 80-120 cm in the alpine but is closer to the surface at and below treeline elevations. Around this crust are facets and potentially surface hoar in sheltered areas. Storm slabs may step down to this layer.

The early-November crust is buried around 100-200 cm at treeline. This crust may have weak and sugary facets above it in parts of the region. This layer has produced large, full-depth avalanches in the past few weeks. Uncertainty remains about where this layer remains a problem in the region, but it may be localized to the northern half of the region.

Terrain and Travel

  • Don't be too cavalier with decision making, storm slabs may remain sensitive to human triggering.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be careful with open slopes and convex rolls, especially in more extreme terrain.
  • Be careful as you transition into wind affected terrain.

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.