Avalanche Forecast

Northwest Inland

Date issued

Nov 30, 2017 - 4:39 PM

Valid until

Dec 1, 2017 - 2:00 PM

Prepared by

swerner

The late October crust near the base of the snowpack is reactive to rider triggers producing large avalanches. You could trigger this from a significant distance away. Heads up out there as this problem will likely persist.

Regular season
Friday - December 1, 2017
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.

Saturday - December 2, 2017
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.

Sunday - December 3, 2017
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

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.

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: Deep Persistent Slabs

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

The late October crust lies near the base of the snowpack with a thin layer of weak, sugary snow above it. This layer has been reactive to rider triggers and remote triggering has occurred.

Travel and Terrain Advice
  • Be aware of the potential for large avalanches due to weak layers at the base of the snowpack.
  • Be cautious in shallow snowpack areas where triggering a deeper layer may be possible.

Avalanche Problem 2: Wind Slabs

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

Recent snow and wind have formed touchy wind slabs. Expect these slabs to be more pronounced at higher elevations and on leeward aspects. Watch for signs of wind affected snow, whumpfing and cracking.

Travel and Terrain Advice
  • Avoid steep convexities and areas with variable snow distribution.
  • Watch for signs of instability such as whumpfing, hollow drum-like sounds or shooting cracks.
  • If triggered the wind slabs may step down to deeper layers resulting in large avalanches.

Avalanche Summary

On Tuesday, skiers up Skilokis Creek area reported remotely triggering a large (Size 2.5) avalanche from 150 m away as they approached a north-facing, treeline bowl. The avalanche was triggered from a shallow snowpack area and failed on a weak facet layer just above the late October crust near the base of the snowpack. The persistent slab was 80 cm deep, 120 m wide and ran 300 m in length. The week before that, several estimated Size 2.5-3 avalanches were observed on the Kathlyn face of Hudson Bay Mountain and are also suspected to have failed on the late October crust. This "crust/facet combo" layer is capable of producing very large avalanche and is expected to remain a layer of concern for some time. Please post your observations to the Mountain Information Network. (MIN)

Snowpack Summary

Average Snowpack depths are 100-140 cm at treeline elevations, and up to 160 cm in the alpine. Approximately 30-40 cm of recent snow now overlies the supportive November 23 crust. This crust extends well into alpine elevations. Below this crust is a well settled mid pack that sits on the widespread late October crust near the base of the snowpack at all elevations. This late October "crust/facet combo" layer has been very reactive to rider triggers producing large avalanches.

Weather Forecast

Friday: Cloudy with possible flurries. Strong ridgetop winds from the West. Alpine temperature -10. Freezing level 500 m and dropping.

Saturday: Mix of sun and cloud. Light ridgetop winds from the North West. Alpine temperature -15. Freezing level valley bottom.

Sunday: Mostly sunny with some residual cloud. Strong ridgetop winds from the North West. Alpine temperature -12. Freezing level valley bottom.

Visit the Mountain Weather Forecast for more details.

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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