Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Sunshine, West Side 93N.
Conditions are tricky now, given recent extreme winds, persistent weak layers, warm temperatures and sun. See the Special Avalanche Warning (SPAW) above for more details.
The Mt. Whymper intermittent closure zone will be closed on Saturday, March 1 for avalanche control. No backcountry activities in this area for the day.
Confidence
High
Avalanche Summary
Some natural activity in the backcountry of both Lake Louise and Sunshine ski hills up to size 2.5. A size 2.5 in the National Goegraphics bowl of the Lake Louise backcountry (see photo) went 60cm deep on the Jan 30th layer, likely triggered by warmth and sun. Natural activity was also noted to size 3 on Mount Whymper in past 24 hours.
On Thursday, helicopter avalanche control on Mt. Field, Stephen, and Dennis produced slab avalanches up to size 3.
Snowpack Summary
Winds in alpine and treeline areas have blown 10 - 30cm of snow from last weekend. This snow sits over previous slabs and is now up to 60cm thick. The slabs sit on weak layers of facets, surface hoar or sun crust formed in late Jan and Feb.
The mid-pack is generally faceted, while depth hoar and crusts form an even weaker base. The snowpack is the weakest in eastern areas where snow depths are low. In these areas, the basal weaknesses should be carefully considered.
Weather Summary
Saturday - Freezing levels up to 2500m, light winds and no snow.
Sunday - much the same
Monday - an upslope storm may bring 5cm in the East, and minimal to the West
Terrain and Travel Advice
- In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and slopes above cliffs.
- Avoid steep, sun-exposed slopes when the air temperature is warm or when solar radiation is strong.
- Watch for newly formed and reactive wind slabs as you transition into wind-affected terrain.
Avalanche Problems
Persistent Slabs
Recent storm snow and extreme winds have added to older slabs. Now up to 60cm thick, these slabs sit over numerous weak layers of facets, surface hoar, or sun crust. Human triggering will remain likely over the short term.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1.5 - 3
Loose Wet
Clear skies and warm temperatures have been a driver for some natural activity (see avalanche table) and smaller, loose, wet avalanches out of steep terrain. These smaller slides could trigger the persistent layers, resulting in bigger slides.
Aspects: South East, South, South West, West.
Elevations: All elevations.
Likelihood: Likely
Expected Size: 1 - 2
Deep Persistent Slabs
The recent storm has added load to an already shallow and weak snowpack. With this additional weight and warmer temperatures, there may be a reawakening of this problem in isolated areas. Areas of concern include thin, shallow, and rocky slopes.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Unlikely - Possible
Expected Size: 1.5 - 2.5