Avalanche Forecast

South Rockies

Date issued

Jan 31, 2018 - 6:04 PM

Valid until

Feb 1, 2018 - 2:00 PM

Prepared by

shorton

Several deeply buried weak layers are a major concern in this region and warrant conservative terrain choices. Stick to simple low-angle terrain and avoid overhead hazards like cornices.

Regular season
Wednesday - January 31, 2018
Alpine

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.

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.

Thursday - February 1, 2018
Alpine

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.

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.

Friday - February 2, 2018
Alpine

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.

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

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.

Avalanche Problem 1: Wind Slabs

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

New snow and strong winds have created wind slabs in leeward areas near ridge crest in the alpine and in exposed treeline areas. Large fragile cornices are also likely near ridge crests.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • If triggered the wind slabs may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for wide propagations due to the presence of hard windslabs.

Avalanche Problem 2: Deep Persistent Slabs

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

Several deeply buried weak layers have the potential to produce large destructive avalanches. Cornices have been a common trigger, so be sure to avoid exposure to overhead hazards.

Travel and Terrain Advice
  • Be aware of thin areas that may propogate to deeper instabilites.
  • Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.
  • Watch for signs of instability such as whumpfing, or shooting cracks.

Avalanche Summary

On Wednesday, a few natural wind slabs (size 2) were reported north of Elkford, including some triggered by cornices. A large deep persistent slab with wide propagation was also reported in alpine terrain. On Tuesday, a few natural wind slabs (size 2) were reported in the southeast part of the region.

During the warm stormy weather on Sunday and Monday a few large deep persistent slab avalanches were reported (up to size 3), most of which were triggered by cornices on north and east facing slopes. Most large slab avalanches have failed on the deeper November and December weak layers.

Snowpack Summary

The most recent snowfall was accompanied with strong gusty winds, leaving touchy slabs in the alpine and large fragile cornices. Warm temperatures on Monday left moist snow and crusts up to about 1700 m.

About 20-50 cm of recent snow covers a weak layer that was buried in mid-January. It is composed of feathery surface hoar in sheltered areas and a sun crust on solar aspects. Another surface hoar layer from early-January is buried 30-60 cm deep. A widespread weak layer from mid-December is composed of facets, crusts, and surface hoar and is now buried 60-80 cm deep. Finally, a weak layer of rain crusts and sugary facets buried in late-November exists near the base of the snowpack.

Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread. Snowpack depths are also variable across the region and typically thinner in northern areas than in areas to the south.

Weather Forecast

THURSDAY: Cloudy with isolated flurries / moderate west wind / alpine temperatures around -10 C.

FRIDAY: Isolated flurries / moderate to strong west wind / alpine temperatures around -7 C.

SATURDAY: Moderate snowfall (amounts uncertain at this point) / strong northwest winds / alpine temperatures around -3 C.

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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