Avalanche Forecast

Northwest Coastal

Date issued

Dec 2, 2017 - 3:55 PM

Valid until

Dec 3, 2017 - 2:00 PM

Prepared by

swerner

The recent storm snow will need time to settle and may be reactive to rider triggers. Storm slab avalanches could step down and trigger deeper layers within the snowpack, initiating large avalanches.

Regular season
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.

Monday - December 4, 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.

Tuesday - December 5, 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.

Avalanche Problem 1: Storm Slabs

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

Storm slabs may be reactive to rider triggers, especially at upper elevations where the storm snow has been affected by wind.

Travel and Terrain Advice
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.
  • Be cautious as you transition into wind affected terrain.

Avalanche Problem 2: Deep Persistent Slabs

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

A lot of uncertainty exists around the reactivity of this layer near the base of the snowpack. A conservative approach to terrain is warranted while the snowpack adjusts to the recent load of storm snow and wind loading.

Travel and Terrain Advice
  • If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.
  • Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Avalanche Summary

Considering the amount of new storm snow there has been no recent avalanche activity reported. I remain suspect of the new snow and the bond to the buried crusts, especially the basal crust. I would be diligent and use a conservative approach to route selection while traveling through low consequence terrain. The new storm snow will need more time to settle and adjust to the layers beneath. Storm slabs may be reactive to rider triggers. Check out the Mountain Information Network for recently posted observations around the Shames area. Give info, get info.

Snowpack Summary

Recent accumulated storm snow amounts are from 100-130 cm and seem to be settling quickly with average snowpack depths 100-150 cm at treeline elevations. Deeper deposits of wind slab may be found on leeward slopes. This storm snow now sits above a 5-10 cm thick crust that was buried a week ago. Digging down 90-160 cm exists a crust/facet combo buried at the end of October. Recent snowpack test results are showing hard compression tests with sudden collapse results. I would keep this on my radar through the weekend to see how the snowpack adjusts to the new load.

Weather Forecast

Sunday: Mix of sun and cloud. Ridgetop winds light from the North West. Alpine temperatures near -6 and freezing levels 500 m.

Monday: Mostly cloudy with up to 10 mm precipitation. Alpine temperatures near 0 degrees and freezing levels rising from 800-1500 m. Ridgetop winds strong from the South West.

Tuesday: Mostly cloudy with light precipitation. Alpine temperatures near 0 degrees and freezing levels 1500 m. Ridgetop winds light from the South West.

Check out the Mountain Weather Forecast for 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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