Avalanche Forecast
Issued: Feb 17th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs and Wind Slabs.
ldreier,
Avalanche Canada
It's going to be a sunny day! However, slabs on the late January persistent weak layer can still be triggered by humans. Don't let your guard down just yet. Read our forecaster blog on "Managing Moderate". Join us for the South Rockies webinar Thursday evening.
Summary
Confidence
Weather Forecast
WEDNESDAY NIGHT: Cloudy with clear periods, trace of new snow, light westerly wind, temperature low -20 C.
THURSDAY: Mostly sunny, moderate southwest wind, temperature high -8 C.
FRIDAY: Mostly cloudy, up to 5 cm new snow, moderate southwest wind, temperature high -6 C.
SATURDAY: Mix of sun and cloud, up to 5 cm of new snow, light to moderate westerly wind, temperature high -5 C.
Avalanche Summary
Several small loose dry avalanches were triggered by skiers on Wednesday. On Tuesday, a natural cornice failure triggered a small avalanche on the slope below in the alpine.
On Monday, skiers triggered size 1 avalanches at treeline and in the alpine on northeast aspects. One avalanche was triggered from a short distance away (see this MIN report). On Sunday skiers triggered avalanches up to size 2.5 on open features at the treeline/alpine interface in the Lizard Range and Tunnel Creek. These failed on the late January persistent surface hoar layer (see this MIN as an example).
On Thursday and Friday there were human and remote triggered avalanches up to size 2 reported. Locations like Mount Fernie, 2000, Liverwurst and McDermid were a few location examples. Some avalanches were triggered from a distance away.
Snowpack Summary
Surface faceting and surface hoar growth continues with clear nights and cold temperatures. Below 1600 m a hard melt-freeze crust is underneath 20-40 cm of recent snow.
A persistent weak layer lurks 30-100 cm below the surface. In some places it consists of surface hoar, in other places just facets, or crust/facet combinations. This weak interface has been responsible for the majority of recent avalanches.
A solid mid-pack sits above a deeply buried crust and facet layers near the bottom of the snowpack (150-200 cm deep), which is currently unreactive.
Terrain and Travel
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
- Avoid terrain traps such as gullies and cliffs where the consequence of any avalanche could be serious.
Problems
Persistent Slabs
Human triggering of this layer is still possible. Small terrain features are producing small avalanche results, bigger features can produce larger more dangerous avalanches. 40-65 cm of snow sits above a buried weak layer consisting of surface hoar, facets, and a crust (depending on elevation and aspect).
The surface hoar interface is the biggest repeat offender, and things have been most reactive on northerly and easterly aspects at treeline and the treeline/alpine interface, but don't let your guard down elsewhere! These kinds of avalanches can happen in surprisingly mellow terrain and can be triggered from a distance away.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Moderate southwest wind will form fresh wind slabs in lee terrain features in the alpine and exposed treeline where soft snow is available for transport.
Look out for wind slabs in unusual places. There have been some localized moderate to strong winds from variable directions over the weekend. Newer reactive wind slabs will be slow to bond where they sit over cold sugary facets. There is also potential for wind slabs to step down to the late January persistent weak layer.
Once the sun comes out wet loose avalanches might release on steep solar aspects.
Aspects: North, North East, East, South East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 18th, 2021 4:00PM
