Avalanche Forecast
Purcells
Winter is loosening its grip as sunshine and warm temperatures team up to test the snowpack in the coming days.
Check out the Forecasters' Blog for more details: http://www.avalanche.ca/blogs/2018-03-09-first-big-warm-up
Avalanche Problem 1: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
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 2: Persistent Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Persistent slabs are most likely to be triggered with a large load like cornice fall; or by a person in a thin or variable-depth snowpack spot.
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
Several more loose dry avalanches to size 2 were observed on Thursday.
A natural cycle of size 1.5-2.5 loose wet avalanches was reported on south-facing slopes on Wednesday. A couple of size 2-2.5 persistent slabs were also observed on south aspects. These most likely failed on a crust buried in February. Some large cornice chunks fell down too.
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 and starts tickling 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
Saturday: A mix of sun and cloud, clearing over the day. Light south winds. Freezing level rising to 1500 metres with alpine high temperatures around -4.
Sunday: A mix of sun and cloud, becoming cloudier over the day. Light southwest winds. Freezing level rising to 1900 metres with alpine high temperatures of -2.
Monday: A mix of sun and cloud. Light south winds. Freezing level rising to 2000 metres with alpine high temperatures of 0.
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New snow and wind have formed variable storm slabs and loose snow conditions, which could be triggered by solar radiation, cornice fall or the weight of a person.