Avalanche Forecast
Purcells
The snowpack is complex with several buried weak layers of concern. A large trigger such as a snowmobile, cornice or wind slab release has the potential to result in a large avalanche. Choose conservative terrain and avoid wind-loaded areas.
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.
- Be cautious as you transition into wind affected terrain.
- If triggered the wind slabs may step down to deeper layers resulting in large avalanches.
Avalanche Problem 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Several troublesome layers exist in the snowpack and may be reactive to large triggers such as a cornice or storm slab release. Human triggering may also be possible in shallow or thin, rocky areas.
Travel and Terrain Advice
- Avoid steep convexities or areas with a thin or variable snowpack.
- Avoid the runout zones of avalanche paths. Very large avalanches have been running full path.
Avalanche Summary
On Sunday there was one report of a naturally triggered size 3 persistent slab avalanche on a west aspect at 2800m that is suspected to have failed due to wind loading and solar inputs. Also, explosive control work continued to produce large, deep avalanches up to size 3 on north to southeast aspects above 2200m. And s skier is believed to have remotely (from a distance) triggered a size 1.5 avalanche on a northwest aspect at 2800m that failed on the early January layer.
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, destroying 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. On Saturday, several cornice-triggered slabs up to size 2.5 were reported above 2400 m.
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. Sun crusts or moist snow may be found on solar aspects and a firm or breakable temperature crust may be found below about 1700 m.
Below the snow surface 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
TUESDAY: Mix of sun and cloud, light flurries. Accumulation up to 5 cm. Ridge wind moderate, southwest. Temperature -8. Freezing level 800 m.
WEDNESDAY: Mostly cloudy, flurries. Accumulation 5-10 cm. Ridge wind light, west. Temperature -12. Freezing level 500 m.
THURSDAY: Mix of sun and cloud. Ridge wind light, southwest. Temperature -15. Freezing level valley bottom.
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New snow and wind will add to recently formed wind slabs and cornices on lee slopes. On solar aspects and at lower elevations the new snow will cover an old crust and may touchy. Pay attention to the bond between the old and new snow.