Avalanche Forecast
Issued: Mar 3rd, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Loose Wet and Persistent Slabs.
astclair,
Avalanche Canada
How buried weak layers in the snowpack will respond to rising temperatures and strong sun is uncertain. The Considerable rating reflects the high likelihood for small loose wet avalanches in many areas and the potential for large persistent slab avalanches in specific areas.
Summary
Confidence
Weather Forecast
Wednesday night: Mostly clear, moderate south wind, freezing level rising to 2200 m.
Thursday: Sunny, light to moderate southwest wind, freezing level rising to 2300 m.
Friday: Increasing cloud, moderate to strong southwest wind, freezing level near 2100 m.
Saturday: Mostly cloudy, 5-10 cm of snow, moderate southwest wind, freezing level near 1500 m.
Avalanche Summary
Numerous large (size 2) natural wet loose avalanches released naturally on south-facing aspects between 1700-2000 m on Wednesday.
Over the weekend, there were a few natural and skier triggered wind slabs size 1.5. On Saturday, large explosive loads produced very large (size 2-3) results at Kootenay Pass. In thin snowpack areas on solar aspects, a few of these large avalanches are suspected to have stepped down to the January layer described in the snowpack summary.
Snowpack Summary
Above freezing temperatures are forecast to reach 2300 m on Thursday with added intensity from strong sun. This rapid warm-up is expected to initiate wet loose avalanche activity and destabilize cornices. Watch for pinwheels and roller balls, as they are a clear indication of this problem. You can avoid them by staying off steep slopes when the snow becomes wet or slushy. Read more about the effects of warming on the snowpack in the Forecaster Blog.
At upper elevations, 20-40 cm of recent snow has seen significant wind effect, with reports of cross-loaded features and scouring on exposed windward aspects. At treeline and below, the recent snow may sit over a layer of small surface hoar crystals in isolated areas.
A persistent layer buried 80-150 cm deep is composed of a combination of surface hoar, crusts, and facets that formed on the surface in late January. The problem seems to be most pronounced in thin snowpack areas on solar aspects. Recently, large explosive loads have been required to trigger an avalanche on this layer, but a rapid rise in temperature may have the potential to initiate these large avalanches.
As described in this MIN report, shallow snowpack areas in the east of the region may harbor a faceted basal snowpack. This structure can typically be managed by avoiding shallow rocky areas where the snowpack transitions from thick to thin. This is another layer that could be susceptible to shock from the warm temperatures this week. Extra caution should be exercised in these types of snowpacks.
Terrain and Travel
- Back off slopes as the surface becomes moist or wet with rising temperatures.
- Extra caution for areas experiencing rapidly warming temperatures for the first time.
- A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
- If triggered loose wet avalanches may step down to deeper layers resulting in larger avalanches.
- Avoid shallow, rocky areas where the snowpack transitions from thick to thin.
Problems
Loose Wet
Loose wet avalanches are most likely on sun exposed slopes and at elevations experiencing above freezing temperatures for the first time. A moist or wet snow surface, pinwheeling or loose wet point releases out of the rocks are good indicators that it is time to back off. Keep in mind that loose wet avalanches and weakened cornices can serve as triggers for persistent slabs.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
There are a few layers of concern with the major warm up happening Thursday:
1) A spotty layer of small surface hoar crystals is buried 20-40 cm deep around treeline. It won't take long for the warm temperatures to affect the snow this depth. We may see isolated avalanche activity on this layer in the early days of the warm up, but beyond that, the warming will likely help this layer heal.
2) A persistent weak layer buried 80-150 cm deep is composed of a combination of surface hoar, crusts and facets formed on the surface in late January. The problem seems to be most pronounced in thin snowpack areas on solar aspects. Recently we have seen large explosive loads and storm slab avalanches in motion produce avalanches on this layer. Rapid warming, strong sun or loose wet avalanches could serve as triggers for large, destructive avalanches this week.
3) Basal facets in shallow snowpack areas in the east of the region could be susceptible to shock from the warm temperatures this week. Extra caution should be exercised in these types of snowpacks. Avalanches on this layer are most likely human triggered from shallow rocky areas, which then propagate out to thicker spots, resulting in large avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Mar 4th, 2021 4:00PM
