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 4th, 2021–Dec 5th, 2021

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

Regions

South Coast Inland.

Modest accumulations of new snow in the south of the region may slide easily on the slick crust. If you see more than 20 cm, consider avalanche danger a step higher. Elsewhere, alpine wind slabs are the main concern, as they may remain reactive to human triggering Sunday.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

Saturday night: 5 cm new snow in the south of the region, a trace elsewhere. Moderate northwest wind. Treeline temperatures around -10.

Sunday: Mainly sunny, isolated flurries. Light to moderate northwest wind. Treeline high temperatures around -12.

Monday: Snow 10-15 cm in the south of the region, a trace elsewhere. Light northwest wind. Treeline high temperatures around -12.

Tuesday: Mainly sunny. Moderate southwest wind building to strong. Treeline high temperatures around -7.

Avalanche Summary

Wind slab was reactive to explosives in the Hurley on Thursday. Reports from explosive control work in the Duffey Lake area Wednesday showed debris from releases up to size 2 (large) scouring to ground in tracks and reaching quite low in runouts. This followed the widespread natural avalanche cycle up to size 3.5 (very large) that occurred over Tuesday night. These sizes suggest that some avalanches may have involved persistent layers discussed in the snowpack summary.

Snowpack Summary

A trace to 15 cm of new snow may sit over a widespread layer of small surface hoar crystals which we will continue to monitor going forward. Dry, wind affected snow can be found in the high alpine. Below 2100 meters, wind-affected snow overlies a thick crust. Below 1800 m a thick, supportive crust caps the snowpack, effectively locking it in place at lower elevations.

A couple of buried weak layers produced large avalanches during a previous storm. Snowpack models and observations in the neighboring Sea to Sky region indicate that these layers have been reset by recent rain at treeline, but uncertainty remains around their status in the alpine. These include a layer of surface hoar down an estimated 90-120 cm and deeper crust/facet combo layer.

Average snowpack depths in the alpine are now likely closer to 150-200 cm. Below treeline, depths of 30-50 cm have been reported around 500 m, decreasing dramatically with elevation, and still below threshold for avalanches in many areas. Early season hazards such as rocks, stumps, and creeks are still a concern below the alpine.

Terrain and Travel

  • Closely monitor how the new snow is bonding to the crust.
  • Keep in mind the crust offers an excellent bed surface for avalanches.
  • Dial back your terrain choices if you are seeing more than 20 cm of new snow.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.