Avalanche Forecast
Regions: Banff, Banff Yoho Kootenay, East Side 93N, Field, Kootenay, LLSA, Lake Louise, Little Yoho, Sunshine, West Side 93N.
Snow and wind on Monday night will hold the danger rating at HIGH in the alpine and treeline, with several natural large avalanches observed running to the valley bottom in the past 24 hrs.
Minimize exposure to avalanche terrain until things improve!
Avalanche control is being conducted on Mt Stephen on Tues Feb 21, 2023. The area is closed.
Confidence
High
Avalanche Summary
Numerous natural avalanches up to size 4 were observed on Monday with debris reaching the bottom of the runout zones in some paths. Ski areas also triggered numerous avalanches with ski cutting and explosives. With additional weather inputs Monday night, forecasters expect the avalanche cycle to continue into Tuesday.
Snowpack Summary
15 to 50+ cm of snow over the past 72hrs 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 40-80 cm below the surface. These weak layers include crusts, facets and surface hoar buried in January, 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 continues to produce sudden test results.
Weather Summary
An additional 10-20 cm of snow is expected Monday night and into Tuesday. The wind will drop to the light to moderate range and switch to a more easterly direction. Temperatures will also start dropping with alpine highs in the -16 to -24°C range as a cold arctic airmass arrives.
More details can be found in the Mountain Weather Forecast.
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
Wind Slabs
15 to 50+ cm of recent snow with consistent strong SW/W wind continues to build slabs and create loose dry avalanches in steep terrain. Use caution in all lee areas with wind effect and watch for wind loading occuring above you. These avalanches may start small, but have the potential to step down to the deeper weak layers and create large avalanches.
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine, Treeline.
Likelihood: Likely - Very Likely
Expected Size: 1 - 2.5
Persistent Slabs
Slabs 50-80 cm deep overly three persistent weak layers formed in January which are a mix of crusts on solar aspect, facets on northerly 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. These avalanches could also step down to the Nov facets and become even larger.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely - Very Likely
Expected Size: 1.5 - 2.5
Deep Persistent Slabs
Facets and depth hoar at the bottom of the snowpack 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 started to see large, destructive avalanches failing on the November facets and running a long distance.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood: Likely - Very Likely
Expected Size: 1.5 - 3.5