Avalanche Forecast
North Columbia
Winter is loosening its grip and a warming event is set 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: Loose Wet
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Travel and Terrain Advice
- Be cautious of sluffing in steep terrain, particularly where the debris flows into terrain traps.
Avalanche Problem 2: Storm Slabs
What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?
Newly formed storm slabs remain a concern, especially on solar aspects where sunshine could act as a natural trigger and where buried crust may act as a sliding layer.
Travel and Terrain Advice
- Use ridges or ribs to avoid pockets of wind loaded snow.
- Give cornices a wide berth when traveling on or below ridges.
- Use extra caution around open slopes and convex rolls
Avalanche Problem 3: 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. Solar warming could also wake up these sleeping beasts.
Travel and Terrain Advice
- Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.
- Pay attention to overhead hazards like cornices which could trigger persistent slabs.
- Avoid convoluted terrain with variable snow depths and multiple trigger points.
Avalanche Summary
Reports from Thursday included several observations of size 1 storm slabs and wind slabs releasing with ski cutting above 1800 metres. One size 1.5 was triggered by a snowmobile. A recent natural size 2 persistent slab avalanche was noted in steep, south-facing alpine terrain. It featured a 70 cm deep crown and is suspected to have failed on a crust from mid-February.
On Wednesday, a few large persistent slabs failed naturally, one with a solar trigger and a couple triggered by icefall. A few small loose and slab avalanches were also reported.
A few large (size 2-3) persistent slabs also failed early this week, both naturally and with a remote trigger. These were reported as failing on the February persistent weak layers on south to west aspects, mostly in the east of the region.
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. A trickier problem will emerge as warmth penetrates into the snowpack to tickle deeper persistent weak layers. This will be a time to avoid exposure to large sunny features and keep well away from corniced slopes.
Snowpack Summary
20-30 cm of new snow has formed storm slabs which overlie sun crusts on solar aspects. This latest snow sits on well-settled storm snow from regular snowfalls over the past couple of weeks. Several other sun crust layers may be found within this storm snow on solar aspects.
A couple of layers buried in mid to late February (down around 60-110 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 linger at the base of the snowpack.
Weather Forecast
Saturday: A mix of sun and cloud, becoming increasingly sunny. Light southeast winds. Freezing level rising to 1400 metres with alpine high temperatures around -4.
Sunday: A mix of sun and cloud. Light south winds. Freezing level rising to 1700 metres with alpine high temperatures of -2.
Monday: Mainly sunny. Light southeast winds. Freezing level rising to 2000 metres with alpine high temperatures around 0 to +1.
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Sun on new snow is likely to lead to loose moist avalanches which could run surprisingly far.