Avalanche Forecast

South Rockies

Date issued

Jan 6, 2018 - 6:28 PM

Valid until

Jan 7, 2018 - 2:00 PM

Prepared by

mgrist

Expect persistent slab avalanche activity to continue as the snow sitting above the persistent weak layer further settles and consolidates. Wind slabs in the alpine and near tree line are a significant concern too.

Regular season
Saturday - January 6, 2018
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Sunday - January 7, 2018
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Monday - January 8, 2018
Alpine

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Below Treeline

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

Avalanche Problem 1: Persistent Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

A weak layer composed of surface hoar and/or crusts is buried 35-70 cm below the surface. This layer continues to be reactive to human triggers and may not improve anytime soon.

Travel and Terrain Advice
  • Watch for signs of instability such as whumpfing, or cracking.
  • Choose supported terrain without convexities at treeline where buried surface hoar may be preserved
  • Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.

Avalanche Problem 2: Wind Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

Strong south west winds have created fresh wind slabs at higher elevations.

Travel and Terrain Advice
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • If triggered, the wind slabs may step down to deeper layers resulting in large avalanches.

Avalanche Summary

Continued avalanche activity was observed in steep low elevation terrain (road cut banks) in the Elk Valley on Wednesday to size 1.5. These were triggering very easily. See here for details in the MIN.

On Monday, a machine triggered Size 1.5 persistent slab avalanche was reported running on the mid December surface hoar layer, down 35 cm at that location (1700m). See the details here in a Mountain Information Network (MIN) post.

Expect to see persistent avalanche activity continue as temperatures revert to a normal regime (warmer in the valleys and colder with elevation) and snow sitting above persistent weak layers settles more rapidly.

Snowpack Summary

Strong to extreme south west winds picked up on Friday and redistributed snow into wind slabs on north through east aspects, as far down as tree line elevations. Some windward slopes have been scoured to ground. Temperatures have also warmed up significantly from the deep freeze, causing the storm snow from late December to settle and take on more slab-like properties at lower elevations

The main concern in the snowpack is a weak layer buried mid-December, which consists of a crust on solar aspects and feathery surface hoar in sheltered terrain at and below tree line. This layer has proven to be reactive to human triggers. The lower snowpack is composed of mostly soft sugary faceted snow and early season crusts.

Avalanche hazard is likely one step lower in areas east of the divide due to shallower snowpacks and the mid-December layer being less prominent.

See here for a recent forecaster blog for a summary of the tricky conditions in the snowpack and strategies on how to work around a persistent slab problem.

Weather Forecast

Occasional flurries with minor accumulations through the forecast period.

SUNDAY: Cloudy with flurries / Moderate to strong west wind / Alpine temperature -4

MONDAY: Cloudy with isolated flurries, accumulation 3-5cm possible / Light southwest wind / Alpine temperature -2

TUESDAY: Flurries becoming snow overnight (5 - 10 cm possible) / Moderate southwest wind / Alpine temperature -4

Danger Ratings Explained

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Natural avalanches possible; human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

4 - High

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Natural avalanches likely; human-triggered avalanches very likely.

Large avalanches in many areas; or very large avalanches in specific areas.

5 - Extreme

Avoid all avalanche terrain.

Natural and human-triggered avalanches certain.

Large to very large avalanches in many areas.

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