Avalanche Forecast

North Columbia

Date issued

Feb 26, 2018 - 4:10 PM

Valid until

Feb 27, 2018 - 2:00 PM

Prepared by

jlammers

Extreme winds will drive the avalanche danger in many areas. The best and safest riding may be found in mellow, sheltered terrain.

Regular season
Tuesday - February 27, 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

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.

Wednesday - February 28, 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

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

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.

Thursday - March 1, 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

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

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.

Avalanche Problem 1: Wind Slabs

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

New snow and continued strong winds will create wind slabs in many areas in the alpine as well as open areas at lower elevations. If triggered wind slabs may "step down" to deeper layers including a weak interface buried mid-February.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • Stay off recent wind loaded areas until the slope has had a chance to stabilize.
  • Make observations and assess conditions continually as you travel.

Avalanche Summary

In recent days, several natural storm slab avalanches to size 2 were observed failing in response to new snow and wind. These avalanches ran on all aspects above 1800m.  A noteworthy event was a naturally-triggered size 3 persistent slab avalanche which failed on the mid-January surface hoar. The avalanche, which is thought to have been triggered by sloughing from above, occurred in the Monashees near Revelstoke on a northeast facing slope at 1900m. This avalanche points to the continued reactivity of deeper persistent slabs in isolated terrain. Continued light snowfall snow and strong winds will promote ongoing wind slab activity, especially in exposed higher elevation terrain.

Snowpack Summary

About 20-50 cm of new snow now covers old surfaces which include faceted powder, a sun crust on solar aspects and surface hoar on shaded, wind-sheltered slopes. I suspect strong winds will have redistributed much of the new snow into fresh wind slabs in exposed terrain. 40-70 cm below the surface lies another interface with similar character and distribution. This layer, which was buried in mid-February, has been reactive in snowpack tests and is definitely worth keeping an eye on as the overlying slab gains thickness and cohesion.

There are several persistent weak layers that are showing signs of improving but still remain suspect as low probability - high consequence avalanche problems. Two surface hoar layers buried in January are now 100-150 cm below the snow surface. Deeper in the snowpack (150 - 200 cm deep) is a facet/crust/surface hoar layer buried in December. Near the base of the snowpack is a crust/facet combo layer buried in late November. These layers may "wake-up" with strong inputs such as solar radiation, rapid loading/warming, or a cornice fall. Human triggering is also possible in shallow, rocky terrain.

Weather Forecast

Tuesday: 5-12cm of new snow / Extreme westerly winds / Alpine temperature of -15

Wednesday: Light flurries / Moderate to strong southwest winds / Alpine temperature of -8

Thursday: Light flurries / Light southerly winds / Alpine temperature of -5

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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