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Avalanche Forecast

Archived

Dec 14th, 2021–Dec 15th, 2021

Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.

Regions

South Rockies.

Adopt a conservative approach to choosing terrain, and avoid thin, rocky start zones. The snowpack appears to be gaining strength, but some persisting weak layers could still be reactive to a rider's weight.

Confidence

Moderate - We are confident about the possible sizes of avalanches, should one release; what is less certain is the likelihood of triggering.

Weather Forecast

The upcoming weather is fairly uneventful. Clouds and light snowfall will be in and out, and the alpine winds will pick up a bit near the end of the week.

TUESDAY NIGHT: Partly cloudy. 0-2cm of snow expected. Light to moderate southwest winds, trending to strong northwest in the alpine. Freezing level dropping to valley bottom.

WEDNESDAY: Scattered clouds. Possible trace of snow expected. Light to moderate southwest winds, trending westerly at higher elevations. Alpine temperatures around -13.

THURSDAY: Partly cloudy. Possible trace of snow. Light to moderate southwest winds, with strong to extreme westerlies on higher peaks. Alpine high around -8.

FRIDAY: Scattered clouds. No new snow expected. Light west winds trending to moderate southwest, and strong northwest in the alpine. Alpine temperatures around -11 with a possible temperature inversion setting up. 

Avalanche Summary

No new natural avalanches observed. 

Avalanche control on Tuesday produced mostly small results on lingering hangfire from Monday's avalanche control. One size 2 explosive triggered avalanche was reported in previously unopened terrain. 

This MIN Report paints a good picture of the avalanche problem right now. They spotted a natural avalanche in a wind loaded feature, and whumpfing in shallow areas.

Reports indicated that the snowpack was quite touchy this weekend. Avalanche control with explosives and ski cuts produced several size 2 avalanches, and one size 3. Most failed on top of the rain crust from the late November/early December rain events.

Snowpack Summary

Yesterday's snow fell with very little wind, so it should be mostly unconsolidated. Where this new snow has been wind transported, (most likely at higher elevations) it could still form reactive slabs. 

Moderate to strong southwest winds during the last storm formed wind slabs that seem to be starting to bond to the early December rain crust, but we're not entirely ready to trust it. This interface was recently active, and a thick crust like this is more likely to encourage faceting.

Snowpack depths are extremely variable due to strong to extreme southwest winds from early December that stripped snow off of exposed areas, and made deep drifts in lee slopes.

Below 2300m, several early season crusts are breaking down and forming a cohesive lower snowpack.

Snowpack depths range from 60-110 cm at treeline elevations. The snowpack tapers quickly below 1900m.

Terrain and Travel

  • Use conservative route selection and resist venturing out into complex terrain.
  • Be careful with open slopes and convex rolls, especially in more extreme terrain.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.