Avalanche Forecast
Issued: Dec 11th, 2020 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs.
JSmith,
Avalanche Canada
Northerly winds may form fresh wind slabs on generally windward aspects that may take riders by surprise this weekend. Use caution when transitioning into wind affected terrain.
Summary
Confidence
Low - Uncertainty is due to the limited number of field observations.
Weather Forecast
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FRIDAY NIGHT: Cloudy / Light, northwest ridgetop wind / alpine low temperature -17 / Freezing level valley bottom.
SATURDAY: Mix of sun and cloud / Light, northwest ridgetop wind / alpine high temperature -11 / Freezing level valley bottom.
SUNDAY: Mix of sun and cloud / Moderate, west ridgetop wind / alpine high temperature -10 / Freezing level valley bottom.
MONDAY: Cloudy / Light, northwest ridgetop wind / alpine high temperature -8 / Freezing level valley bottom.
Avalanche Summary
On Thursday, natural wind slab avalanches were reported up to size 2. The recent storm snow is not bonding well to the underlying crust. Wind slabs may be reactive to human triggers at treeline and above on Saturday.
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Snowpack Summary
10- 20 cm of recent snow fell at upper elevations while the rest of the precipitation came in as rain or freezing rain. Recent reports suggest that the freezing rain occurred from 1800m to 2000m “ish†with rain at lower elevations which may have destroyed the surface hoar at 2000m and below. All elevations are now hosting a burley crust under the new snow.
Up high, stiff wind slab exists on leeward slopes where the new snow deposits into deeper drifts, especially where the new snow sits above this recent rain/freezing rain crust, or the older melt-freeze crust found on solar aspects. Digging deeper in the snowpack two crusts exist from November. One down approximately 30 cm, just below the old surface hoar, and the other sits deeper (down 70-90 cm) and is widespread up to 2500 m. The deeper crust seems to be bridged by a well-consolidated mid-pack in most areas. These crusts have shown no recent reactivity in snowpack testing but remain on our radar moving forward.
The snowpack is generally thin, wind hammered, variable in wind-scoured areas, and tapers rapidly at lower elevations. Snowpack depths at sheltered upper treeline elevations are nearing 100 cm and beginning to exceed the threshold for avalanches.
Terrain and Travel
- Avoid areas where the snow feels stiff and/or slabby.
- Closely monitor how the new snow is bonding to the crust.
- Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
- Recent wind has varied in direction so watch for wind slabs on all aspects.
Problems
Wind Slabs
The recent snow has a poor bond to the underlying crust. Isolated pockets of stiff wind slab could be reactive to human triggers especially where it sits on a widespread crust. Loose-dry sluffing may be seen from steeper slopes and terrain features.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Dec 12th, 2020 4:00PM
