Avalanche Forecast

Archived

Feb 23rd, 2021–Feb 24th, 2021

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

South Rockies.

Don't let your guard down during clear skies; recently formed slabs and a buried weak layer can still be triggered by riders.

Confidence

Moderate - Uncertainty is due to the limited number of field observations.

Weather Forecast

TUESDAY NIGHT: Partly cloudy, 20 km/h northwest wind, alpine temperature -12 C.

WEDNESDAY: Clear skies, 20 km/h west wind, alpine temperature -11 C.

THURSDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 30 to 60 km/h southwest wind, alpine temperature -9 C.

FRIDAY: Cloudy with snowfall, accumulation 5 to 10 cm, 30 to 40 km/h west wind, alpine temperature -9 C.

Avalanche Summary

We've only received a few reports of storm slab avalanches around 30 cm deep on Monday, localized in the southwest of the region. However, visibility was poor, so the extent of activity likely couldn't be seen.

Looking towards Wednesday, natural avalanche activity is expected to diminish, except perhaps on steep southerly slopes from solar warming. Human triggering of storm, wind, and persistent slabs will remain possible.

Snowpack Summary

Anywhere from 10 to 50 cm of snow fell on Monday and Tuesday, with the most in the south and west of the region near the divide. In areas where more snow fell, storm slabs may remain reactive to human traffic, particularly where it overlies sugary faceted grains from recent cold air. The wind was howling from the south during the storm, which formed wind slabs in exposed terrain.

Around 50 to 80 cm deep, a weak layer of surface hoar may be found in sheltered terrain or otherwise faceted grains and/or a hard melt-freeze crust. This layer has so far shown to be most problematic around the Elk Valley, but you may find it elsewhere.

Weak faceted grains and a decomposing melt-freeze crust are likely found near the base of the snowpack. There have not been recent avalanche observations on this layer, but steep and rocky slopes as well as shallow snowpack areas should be approached with caution.

Terrain and Travel

Choose conservative terrain and watch for clues of instability.
Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
Be aware of the potential for large avalanches due to the presence of buried surface hoar.
Minimize exposure to sun-exposed slopes when the solar radiation is strong.
Pay attention to cornices and give them a wide berth when traveling on or below ridges.

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.

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.