Avalanche Forecast
Issued: Mar 7th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Cornices.
mconlan,
Avalanche Canada
Buried weak layers remain possible to be triggered by riders, where they exist. Cornices and sun-exposed slopes will deteriorate during the heat of the day, potentially increasing the likelihood of avalanche activity.
Summary
Confidence
Weather Forecast
SUNDAY NIGHT: Cloudy with light snowfall then clearing, accumulation 1 to 3 cm, 20 km/h southwest wind, alpine temperature -8 C.
MONDAY: Clear skies, 10 km/h northwest wind, alpine temperature -9 C, freezing level rising to 1500 m.
TUESDAY: Mix of sun and cloud, 20 km/h southwest wind, alpine temperature -6 C.
WEDNESDAY: Mix of sun and cloud with afternoon snowfall, accumulation 2 to 5 cm, 20 km/h west wind, alpine temperature -9 C.
Avalanche Summary
We received a few images of a rider that triggered a persistent slab avalanche near Crowsnest Pass on Saturday. The avalanche appeared to be large (size 2 or greater) and at below treeline or treeline elevation in a forest burn. It is suspected that the avalanche released on one or potentially both of the weak layers described in the Snowpack Summary, as the maximum slab depth was around 90 cm.
Otherwise, a few persistent slab avalanches were triggered naturally in adjacent Waterton National Park on Saturday. The avalanches were on northeast aspects between 1600 and 2000 m and released on the mid-February layer described in the snowpack summary.
Snowpack Summary
Previous warm air temperature followed by a re-freeze have created a melt-freeze crust on the snow surface on sun-exposed slopes and below treeline. Dry snow may still be found on north aspects at treeline and alpine elevations. Wind slabs are likely still present on northerly aspects in the alpine and at treeline. Windward slopes at upper elevations have been scoured down to rocks or crusts in many areas due to recent strong southwest winds.
Around 40 to 60 cm of snow sits above a persistent weak layer of sugary faceted grains that was buried in mid-February. There have been a handful of avalanches that released on this layer in the past few weeks. There is another persistent weak layer that was buried at the end of January, found around 50 to 80 cm deep. This layer consists of feathery surface hoar, facets, and/or a hard melt-freeze crust. Periodic avalanches continue to be triggered on these layers.
Weak faceted snow and a decomposing melt-freeze crust can be found near the base of the snowpack.
Terrain and Travel
- Be aware of the potential for large avalanches due to the presence of a persistent slab.
- Avoid exposure to steep, sun exposed slopes, especially when the solar radiation is strong.
- When a thick, melt-freeze surface crust is present, avalanche activity is unlikely.
Problems
Persistent Slabs
Two persistent weak layers exist in the snowpack:
- The upper layer is buried 30 to 60 cm and primarily consists of faceted grains.
- The deeper layer is buried 60 to 100 cm and consists of surface hoar, facets, and/or a crust. The problem has been most prevalent around treeline elevations and in openings below treeline, but also reaches into the lower alpine.
These layers could be triggered by riders anywhere they still exist. A warm and sunny Monday may increase the likelihood of triggering these layers.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Cornices
Cornices will weaken with sunny skies and relatively mild air temperature. The snow on sun-exposed slopes may also weaken, so use caution during the heat of the day.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine.
Likelihood
Expected Size
Valid until: Mar 8th, 2021 4:00PM
