Avalanche Forecast
Purcells
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Avalanche Problem 1: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Give cornices a wide berth when travelling on or below ridges.
- Travel on ridgetops to avoid wind slabs on slopes below.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Several troublesome layers are producing very large, destructive avalanches. These could be triggered by the weight of a person or snowmobile, or a surface avalanche.
Travel and Terrain Advice
- Use conservative route selection. Choose low-angle, supported terrain with low consequence.
- Avoid the runout zones of avalanche paths. Very large avalanches have been running full path.
Avalanche Problem 3: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Recent storm snow is gradually stabilizing, but storm slabs can still be triggered by solar warming or cornice fall, or a person in specific areas.
Travel and Terrain Advice
- If triggered, storm slabs may step down to deeper layers and result in large avalanches.
- Choose shallow-angled and sheltered terrain where new snow hasn't been wind-affected.
- Avoid exposure to sun-exposed slopes.
Avalanche Summary
A very large, widespread avalanche cycle was observed on Thursday, and explosives control continued to get large results on Friday. Slopes of all aspects and elevations ran, some going full path to valley floor, smashing mature timber. These failed on all of the persistent weak layers discussed in the snowpack section. Avalanches involving only the recent storm snow were also very large.
The natural cycle is winding down, but human-triggering remains a real concern. You might be surprised by how large an avalanche can be triggered and how far it could run.
Snowpack Summary
30-60 cm recent storm snow may have been shifted into wind slabs on slopes lee to recent south-west through north-west winds. Fragile cornices can be found in some areas. Sun crusts or moist snow may be found on solar aspects.
Several persistent weak layers make up a troublesome snowpack which is not tolerating the recent load. In the top 1-2 m of the snowpack, two surface hoar/ crust layers buried in January can be found. Expect to find one or other of these on all aspects and elevations.
Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.
Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.
All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.
Weather Forecast
An Arctic air mass keeps things cold and dry until Tuesday, when there is a change to cloud, milder temperatures and moderate south-westerly winds.
More details can be found in the Mountain Weather Forecast.
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Recent north-westerly winds have left behind wind slabs and cornices on lee slopes.