Avalanche Forecast

North Columbia

Date issued

Feb 12, 2018 - 4:57 PM

Valid until

Feb 13, 2018 - 2:00 PM

Prepared by

jmcbride

A strong system with periods of intense snowfall and high winds will increase avalanche danger on Tuesday. Stick to low-angle, simple terrain and avoid areas with overhead hazard. Large avalanches may run long distances.

Regular season
Monday - February 12, 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

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.

Below Treeline

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.

Tuesday - February 13, 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

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.

Wednesday - February 14, 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

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: Storm Slabs

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

New snow and wind will form touchy storm slabs. These slabs will cover a variety of old surfaces including extensive wind slabs at upper elevations and crusts on solar aspects and at lower elevations. Pay attention to how the new snow is bonding.

Travel and Terrain Advice
  • If triggered, wind slabs may step down to deeper layers resulting in large avalanches.

Avalanche Problem 2: Persistent Slabs

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

Several troublesome layers exist in the snowpack and may be reactive to large triggers such as a cornice or storm slab release. Human triggering may also be possible in shallow or thin, rocky areas.

Travel and Terrain Advice
  • Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.
  • Be aware of the potential for large, deep avalanches.
  • Avoid steep convexities or areas with a thin or variable snowpack.

Avalanche Summary

Monday skiers remotely triggered (from a distance) a size 3.5 from 40 m away on a ridgeline adjacent to a south-facing slope at 2600 m.

On Sunday explosive control work north of Revelstoke produced storm slab results from size 1.5-2.5 and two size 3 deep slab failures (120-170 cm deep) on a east aspect at 2400 m.

A very large, widespread avalanche cycle was observed on Thursday, with a few events continuing on Friday and Saturday. Slopes of all aspects and elevations ran full path and reached valley floor. In some cases, mature timber was smashed. These failed on all of the persistent weak layers discussed in the snowpack section. Avalanches involving only the recent storm snow were also very large. Explosives continued to produce very large persistent slabs on Saturday.

Snowpack Summary

Strong north to north-westerly winds have shifted 25-70 cm recent storm snow into wind slabs on lee slopes. Alpine and open treeline areas have seen extensive wind-affect, while a sun crust exists on solar aspects and a rain crust can be found below 1600 m.

Below the snow surface, several persistent weak layers make up a troublesome snowpack. In the top 1.5-2.5 m of the snowpack, two surface hoar layers buried in January can be found. Expect to find one or other of these on all aspects and elevations.

Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.

Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.

All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.

Weather Forecast

TUESDAY: Snow. Accumulation 10-20 cm. Ridge wind moderate to strong, southwest. Temperature -10. Freezing level valley bottom.

WEDNESDAY: Mostly cloudy, light flurries. Accumulation trace. Ridge wind light, west. Temperature -10. Freezing level valley bottom.

THURSDAY: Mix of sun and cloud. Ridge wind light, south. Temperature -12. Freezing level valley bottom.

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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