Avalanche Forecast
Issued: Mar 4th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs, Persistent Slabs and Wind Slabs.
trettie,
Avalanche Canada
Avoid shallow rocky terrain where the snowpack transitions from thick to thin. Terrain features that fit that description at upper treeline and in the alpine are especially concerning. This is where riders are most likely to trigger a large destructive deep persistent slab avalanche.
Be prepared to back off slopes if the surface gets moist from solar input. This time of year it only takes a short period of strong solar to increase hazard.
Summary
Confidence
Moderate
Avalanche Summary
On Wednesday a fatal avalanche incident involving a group of skiers occurred in the Purcell Mountains west of Invermere BC. The size three avalanche was triggered on a southwest facing slope at 2500 m. The weak layer of facets buried in late November That sits at the bottom of the snowpack was responsible. Very large avalanches failing on this layer are most likely to be triggered in shallow rocky terrain with variable snowpack depths at upper treeline and in the alpine.
This MIN shows some large naturally occurring deep persistent slab avalanches. These avalanches likely occurred earlier in the week.
Earlier in the week several skier triggered avalanches were reported. Two of these avalanches were remotely triggered. Surface hoar layers from January and February were initially triggered. In one case the avalanche then stepped down to the facets at the bottom of the snowpack. These avalanches occurred at treeline and above and on a variety of aspects.
Snowpack Summary
Up to 40 cm of storm snow from earlier in the week sits over wind affected surfaces. Expect deeper deposits on north and east facing slopes, from west through south winds.
Buried surface hoar sits 30-60 cm deep in sheltered terrain features, and a thin sun crust exists at the same depth on steep south-facing terrain. Several other layers from January can also be found in the top 100cm of the snowpack.
The lower snowpack is made up of a widespread layer of large, weak basal facets and depth hoar in some areas. this weakness has been responsible for a number of recent very large, destructive avalanches and will continue to be a concern.
Weather Summary
Saturday Night
Mostly cloudy with the possibility of light flurries bringing a few centimeters of new snow. Light to moderate southeast winds and a low of -13°C at 2000 m.
Sunday
A mix of sun and cloud with the possibility of light flurries bringing a few centimeters of new snow. Light to moderate southeast winds and a high of -8°C at 2000 m.
Monday
A mix of sun and cloud with the possibility of light flurries bringing trace amounts of new snow. Light variable winds and a high of -7°C at 2000 m.
Tuesday
Sunny with no new snow expected. Light southwest winds and a high of -7°C at 2000 m.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Avoid areas with a thin or variable snowpack.
- Avoid steep, rocky, and wind effected areas where triggering slabs is more likely.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
- Remote triggering is a concern, watch out for adjacent and overhead slopes.
- Avoid exposure to steep sun exposed slopes.
Problems
Deep Persistent Slabs
The base of the snowpack remains very weak. Very large human triggered avalanches are possible at treeline and above . Avoid shallow and rocky areas, where the snowpack depth is highly variable. This is a very concerning avalanche problem and should stay in your mind when traveling in the backcountry.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
Weak layers from January and February have recently produced human triggered avalanches at treeline and above on a variety of aspects. On shaded slopes these layers will generally present as surface hoar and on sun exposed slopes they will generally present as facets and a crust.
Avalanches triggered on these layers can step down to the facets at the bottom of the snow pack resulting in a very large avalanche.
These layers can be remotely triggered. Avoid travelling below steep slopes.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Wind Slabs
Previous moderate winds and recent storm snow have built reactive slabs at higher elevations. Wind slabs are most likely to be found on north and east aspects
Wind slab avalanches can step down to deeper layers..
Aspects: North, North East, East, South East, South, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Mar 5th, 2023 4:00PM
