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Avalanche Forecast

Dec 26th, 2020–Dec 27th, 2020
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
3: Considerable
The avalanche danger rating below treeline will be considerable
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate
Alpine
3: Considerable
The avalanche danger rating in the alpine will be considerable
Treeline
3: Considerable
The avalanche danger rating at treeline will be considerable
Below Treeline
2: Moderate
The avalanche danger rating below treeline will be moderate

Regions: Purcells.

  

Buried weak layers in the middle and bottom of the snowpack continue to be a significant concern. Conservative terrain choices are key to avoiding these large and destructive avalanches.

Confidence

Moderate - Uncertainty is due to the limited number of field observations. Uncertainty is due to the fact that deep persistent slabs are particularly difficult to forecast.

Weather Forecast

 SATURDAY NIGHT: Cloudy with flurries; 0-3 cm. / Moderate to strong, northwest ridgetop wind / alpine low temperature -12 / Freezing level valley bottom.

SUNDAY: Mostly cloudy with sunny periods. / Light, northwest ridgetop wind / alpine high temperature -8 / Freezing level valley bottom.

MONDAY: Cloudy / Light, northwest ridgetop wind / alpine high temperature -9 / Freezing level valley bottom.

TUESDAY: Mix of sun and cloud / Light, northwest ridgetop wind / alpine high temperature -10 / Freezing level valley bottom.

Avalanche Summary

On Wednesday there was a report of a snowmobile triggered size 2 deep persistent slab avalanche in the north of the region. This MIN post highlights the avalanche and the current nature of the snowpack.

On Tuesday there were several reports of deep persistent slab avalanches running size 2-3 on southeast, east and northeast aspects. Three of these were size 2's triggered by skiers. Check out this MIN report from Tuesday afternoon for an example. 

Snowpack Summary

30 to 75 cm. of storm snow fell last weekend and into Monday. Winds blowing from a variety of directions formed slabs in lee features at upper elevations, reactive cornices have grown too. 

Below the storm snow, there are several critical layers of concern. The early December surface hoar is down 30 to 80 cm. It has recently been sensitive to remote triggering which is well illustrated in this MIN post from the Golden area.

Below, or near the surface hoar you may encounter a crust. This crust has been observed as high as 2400 m. in the south of the region and 1800 m. in the north.  

The lower snowpack is characterized by more crusts, the most notable is a rain crust from early November that is 50 to 130 cm deep. This crust is sitting near the base of the snowpack, surrounded by a weak layer of sugary facets. It is most likely to be reactive to human triggers in steep, shallow, rocky areas with a thin to thick snowpack.

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Remote triggering is a concern, watch out for adjacent and overhead slopes.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

Avalanche Problems

Wind Slabs

Wind switching directions has created wind slabs on a variety of aspects.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible - Likely

Expected Size: 1 - 2

Persistent Slabs

A weak layer of surface hoar down 40-90 cm. has been reactive to human triggers, resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1.5 - 2.5

Deep Persistent Slabs

A Crust buried near the bottom of the snowpack has been responsible for some very large explosive triggered avalanches up to size 4.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible

Expected Size: 2.5 - 4