Avalanche Forecast
Issued: Feb 19th, 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
Don't let your guard down just yet! Persistent slabs continue to be easily triggered by human traffic. Consider the consequences if an avalanche released. Recently triggered avalanches reached up to size 2.5 and are definitely large enough to bury, injure or kill a person.
Summary
Confidence
Weather Forecast
FRIDAY NIGHT: Cloudy with clear periods, trace of new snow, moderate southwest wind, temperature low -11 C.
SATURDAY: Mostly cloudy, 3 cm new snow, moderate southwest wind, temperature high -6 C.
SUNDAY: Cloudy, 10-15 cm new snow, strong southwest wind, temperature high -2 C, freezing level rising to 1500 m.
MONDAY: Cloudy, 20-30 cm new snow and rain at lower elevations, strong southwest wind, temperature high 0 C, freezing level at 1700 m.
Avalanche Summary
A small persistent slab avalanche was triggered remotely by a rider below treeline (see this MIN report) on Thursday. Whumpfing and shooting cracks were reported by several parties.
More reports of easily triggered persistent slab avalanches came in on Wednesday, including these large avalanches at treeline on Mt. Fernie. These new reports highlight the persistent slab problem has not gone away yet. There were also several small loose dry avalanches which were triggered by skiers.
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).
Reports on human and remote triggered persistent slab avalanches up to size 2.5 continue since last week. Locations like Mount Fernie, 2000, Liverwurst and McDermid are a few location examples. Some avalanches were triggered from a distance away.
Snowpack Summary
A few centimetres of new snow sit on surface hoar and thick layers of faceted snow. Below 1600 m a hard melt-freeze crust is underneath 20-40 cm of recent snow.
A persistent weak layer lurks 40-70 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
- The trees are not the safe-haven they normally are at this time. Terrain at treeline is primed for human triggered avalanches.
- Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
- Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Problems
Persistent Slabs
This layer continues to be easily triggered by skiers and riders. Small terrain features are producing small avalanche results, bigger features produce larger more dangerous avalanches. 40-70 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. This MIN report from Wednesday is a good illustration.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Moderate southwest wind will continue to form wind slabs in lee terrain features in the alpine and exposed treeline.
Look out for wind slabs in unusual places. There have been some localized moderate to strong winds from variable directions over last weekend. These wind slabs are 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.
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 20th, 2021 4:00PM
