Avalanche Forecast
Purcells
Avalanche danger will increase in the afternoon with strong solar input and warming temperatures. Concern for persistent slab problems is on the rise.
See the Forecaster's Blog for more: http://www.avalanche.ca/blogs/2018-03-09-first-big-warm-up
Avalanche Problem 1: Loose Wet
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Avoid exposure to sunny slopes, especially in the afternoon.
- Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
Avalanche Problem 2: Wind Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Recent snow and wind have formed variable wind slabs and loose snow conditions. Slab and loose wet avalanches may be triggered by solar radiation on solar slopes, by cornice fall, or with the weight of a person.
Travel and Terrain Advice
- Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.
- Use ridges or ribs to avoid pockets of wind loaded snow.
- Extra caution needed around cornices with current conditions.
Avalanche Problem 3: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Rising temperatures and strong sunshine are increasing concern for weak layers buried deep in the snowpack. In addition to human triggering in thin spots, solar warming and cornice releases are possible natural triggers for persistent slabs.
Travel and Terrain Advice
- Pay attention to overhead hazards like cornices which could potentially trigger the persistent slab.
- Avoid steep convexities or areas with a thin or variable snowpack.
- Choose regroup spots away from avalanche paths.
Avalanche Summary
On Sunday we received preliminary reports of a skier caught in a size 2.5 avalanche in the north of the region. The slab was 20-50 cm thick and started on a steep north east aspect immediately below ridge crest at 2300m.
Reports from Friday included observations of numerous storm slabs and wind slabs that generally ran from size 1 to 2. These were triggered naturally as well as with ski cutting and all aspects and elevations were represented. Numerous loose wet avalanches were observed in the region as well.
Avalanche activity is expected to increase as we move into a period of intense sun and prolonged warming. Predictable loose wet avalanches from steep, sunny terrain should be easy to manage. The trickier beast will be when warmth penetrates into the snowpack to tickle deeper persistent weak layers. The next few days will be a time to avoid exposure to large sun-exposed features and keep well away from corniced slopes.
Snowpack Summary
Around 10-15 cm new snow has formed storm slabs that overlie a sun crusts on solar aspects. A couple of layers buried in mid-late February (down around 40-100 cm) are variably reactive, but both have the potential to create surprisingly large avalanches if triggered. Initially, these interfaces were most reactive on solar aspects, where they present as buried sun crusts. However, persistent slabs have been triggered on shady aspects too, where surface hoar and/or facets exist.
Deeper persistent weak layers from January and December are generally considered dormant, but could wake up with forecast warming, a surface avalanche stepping down, cornice fall, or a human trigger in a shallow or variable-depth snowpack area. These layers consist of sun crust, surface hoar and/or facets. Facets also linger at the base of the snowpack.
Weather Forecast
Sunny and warm until the start of our next weather system on Wednesday.
MONDAY: Sunny. Light southeast winds. Freezing level rising to 2200 metres with alpine high temperatures around +2.
TUESDAY: Mainly sunny. Light southeast winds, increasing over the day. Freezing level to 2500 metres with alpine high temperatures of +3.
WEDNESDAY: Cloudy with isolated flurries in the afternoon. Light south winds. Freezing level falling to 2000 metres with alpine high temperatures of +1.
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Wet loose avalanches are likely in steep, rocky, sunny terrain. Warming could also wake up more deeply buried weak layers, creating a surprisingly large avalanche.