Avalanche Forecast

Cariboos

Date issued

Feb 6, 2018 - 4:29 PM

Valid until

Feb 7, 2018 - 2:00 PM

Prepared by

mconlan

Substantial snowfall is forecasted, which will rapidly load several buried weak layers. Travel in avalanche terrain is not recommended, as widespread avalanche activity is expected. Below treeline, avoid open slopes and overhead exposure.

Regular season
Tuesday - February 6, 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

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 7, 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.

Thursday - February 8, 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: Storm Slabs

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

Up to 40 cm of snow is forecasted for Wednesday. The new snow as well as previously formed storm and wind slabs will likely be reactive to both natural and human triggering. If triggered, avalanches could step down to deeper weak layers.

Travel and Terrain Advice
  • A good day to avoid avalanche terrain, giving wide berth to overhead exposure.
  • If triggered, the storm/wind slabs may step down to deeper layers, resulting in large avalanches.
  • Choose shallow-angled and sheltered terrain where new snow hasn't been wind-affected.

Avalanche Problem 2: Persistent Slabs

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

Several weak layers are lurking in our snowpack, which are producing very large avalanches that propagate far, with high consequences. Rapid snowfall will load these layers, increasing the likelihood of triggering them.

Travel and Terrain Advice
  • Be aware of the potential for wide propagation.
  • Avoid open slopes and convex rolls where buried surface hoar may be preserved.
  • Avalanches could run full-path: avoid runout zones of avalanche paths.

Avalanche Summary

On Monday, loose dry avalanches were observed from solar aspects during the heat of the day.  Otherwise, more evidence of a natural avalanche cycle from Friday to Sunday was noted.  Many slabs were observed, which were expected to have released during the storm.  This includes many wind, storm, and persistent slab avalanches, from small to large (size 1 to 3).  The slabs were 30 to 200 cm deep, on all aspects, and most often at upper below treeline, treeline and alpine elevations.  Many of the releases were highly destructive, such as this one, highlighting the consequence if an avalanche is triggered.

Looking forward, dangerous snowpack conditions will exist on Wednesday with new snowfall and strong winds. All of our buried weak layers (described in the section below) continue to produce large destructive avalanches from natural and human triggers. New storm slabs and wind slabs have the potential to step down to deeper weak layers, which could produce large, destructive avalanches.

Snowpack Summary

Up to 40 cm of snow could accumulate in the region by Wednesday afternoon.  This overlies 40-100 cm of storm snow from the past two weeks that has formed a slab that sits over an unstable snowpack.  There are three active weak layers that we are monitoring:

1) The first layer is buried around 70 to 100 cm and is formed of a crust and/or surface hoar layer that was buried in mid-January. The surface hoar is up to 10 mm in size, found at all elevation bands and has been very reactive on north through east aspects between 1900-2600 m.

2) Deeper in the snowpack, the early-January persistent weak layer is found 60 to 120 cm below the surface. This layer was reported as the most active persistent weak layer during a recent natural avalanche cycle that took place in the region. It was also very reactive to recent explosives control.

3) Another weak layer buried mid-December consists of a facet/surface hoar/crust combination, which is 100 to 180 cm deep. It has been most problematic at and below tree line.

Weather Forecast

TUESDAY NIGHT: Cloudy with snowfall, accumulation 10 to 20 cm, moderate westerly winds, alpine temperature near  -10 C, freezing level below valley bottom.

WEDNESDAY: Cloudy with snowfall, accumulation 10 to 15 cm, light to moderate westerly winds, alpine temperature near -6 C, freezing level near valley bottom.

THURSDAY: Cloudy with light snowfall early morning, accumulation 10 to 15 cm, light to moderate westerly winds, alpine temperature near -10 C, freezing level below valley bottom.

FRIDAY: Mostly sunny with possible valley cloud, light to moderate northwesterly winds, alpine temperature near -14 C, freezing level below 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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