Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
Recent snow inputs and winds have loaded lee terrain creating fresh new slabs, developed cornices , and generated extensive loose dry sluffs out of very steep terrain ... all of these elements represent moving snow which provides the potential to trigger slabs.
Meanwhile the slabs overlying the persistent and particularly, the deep persistent, weak layers are showing signs that they have reached their tipping point and are ripe for triggering.
Climbers and Skiers alike should avoid overhead avalanche terrain and make very conservative terrain decisions should they choose to travel at all.
Confidence
Moderate
Avalanche Summary
A flight in the Northern part of the park Friday saw continued natural activity over the past 24 hours. Mainly wind slabs with some stepping down to persistent or deep persistent layers. Lake Louise observed a natural size 2.5 on "Speed run", and a natural size 3 in Richardson's bowl. Both initiated on the basal facets. As well, lots of recent explosive triggered and natural avalanches.
A size 2.5 deep persistent natural avalanche at Quartz ridge was triggered by a cornice on Thursday. There was also a MIN report of a skier remote triggering a size 2.5 avalanche in the Healy Creek area on Wednesday from 100m away showing continued reactivity to a skier's weight.
Snowpack Summary
10 to 25 cm of snow over the past 48hrs with moderate to strong SW-W winds have created extensive wind effect in the alpine and contributed to wind slab development. Several persistent weak layers exist 30-60cm below the surface. These weak layers include crusts, facets and surface hoar buried in January and are producing sudden test results in some locations. Deeper in the snowpack, the November crust/facet layer is found about 40 cm above the ground and also continues to produce sudden test results.
Weather Summary
Overnight into Sunday NW winds will strengthen to 50 to 60km/h and alpine temps will fall to -10 to -15C.
A low pressure system will impact the region Saturday with 5-10cm of snow, strong NW winds will shift W, temps will rise to -4 to -8C in the alpine during the day.
Overnight into Sunday, the cold front associated with the low will bring another 5 to 10 cm of snow and alpine temperatures will drop to -5 to -10C. Winds will weaken to 40 to 50km/h by morning.
A second westerly system will collide with cold northern air dropping down the prairies on Monday: significant snowfall is expected with dropping temperatures.
Terrain and Travel Advice
- Make conservative terrain choices and avoid overhead hazard.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Cornice failure may trigger large avalanches.
Avalanche Problems
Persistent Slabs
Slabs 30-60 cm deep overlie three persistent weak layers formed in January which are a mix of crusts (solar aspect), facets (cold aspects) and isolated surface hoar. We have primarily seen avalanches failing on crusts on solar aspects but examples have been seen on other aspects as well.
Aspects: South East, South, South West, West.
Elevations: Alpine, Treeline.
Likelihood: Likely
Expected Size: 1 - 2.5
Deep Persistent Slabs
20 to 50cm above the ground facets and depth hoar near a crust formed in November provide weak support for the entire snowpack. Incremental snowfall since the start of February has brought the overlying slab to the tipping point and we have starting to see signs that the weak base is becoming overloaded. The snowfall and wind expected through Tuesday are likely to cause large, destructive avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Possible - Likely
Expected Size: 1.5 - 3.5
Wind Slabs
5-20cm of new snow overnight adds to previous wind slabs formed from strong winds over the past week. Use caution in all leeward areas with wind effect. These avalanches have the potential to start small, but then step down to the deeper weak layers.
Aspects: North, North East, East, South East, South.
Elevations: Alpine, Treeline.
Likelihood: Very Likely
Expected Size: 1 - 2