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Avalanche Forecast

Archived

Mar 8th, 2020–Mar 9th, 2020

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches possible, human triggered probable.
Treeline
Natural avalanches possible, human triggered probable.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Northwest Inland.

Don't let the amazing riding lure you out into the biggest terrain features just yet, we've got active persistent slab problems in play that may remain sensitive to human triggering.  

Confidence

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

The storms just keep coming.

SUNDAY NIGHT: Freezing level at valley bottom, moderate southwest wind, trace of snow possible.

MONDAY: Overcast, freezing level near valley bottom, moderate southwest wind, 4 to 8 cm of new snow during the day, 5 to 10 cm Monday Night.

TUESDAY: Overcast, freezing level rising to about 1000 m, strong southwest wind, 5 to 10 cm of snow during the day, 1 to 5 cm Tuesday Night.

WEDNESDAY: Broken cloud cover, freezing level at valley bottom, moderate west/northwest wind, trace of snow possible.

Avalanche Summary

Avalanche activity slowed down Saturday, aside from the observation of some older wind slabs in steep terrain very little avalanche activity was observed.  

Last week there were reports of wind slab, persistent slab (failing on the February 19 surface hoar layer), and deep persistent slab (failing on basal facets) avalanches. This pattern highlights loading and surface avalanches from recent stormy weather straining multiple weak layers in the snowpack.

Reports from Thursday showed several more wind and storm slab avalanches from size 1-2 (small to large) releasing naturally as well as with skier and snow machine traffic in the Kispiox area. North through east aspects again proved most reactive.

On Wednesday a cornice failure in the same area initiated a size 3 wind slab avalanche on a northeast facing feature at 1600 m that cleared out large timber in the valley. The recent storm snow was sensitive to human triggering, even in low angle terrain, running on the March 1st surface hoar. A few shallow natural wind slabs were also observed in steep terrain.

Cornice falls have been a common trigger for slabs on the slopes below them. On February 28th a cornice fall triggered a size 3.5 deep persistent slab on a northeast facing slope at 1800 m.

Snowpack Summary

The Wednesday into Thursday night storm produced 5 to 25 cm of new snow with the deepest accumulations found in the south and accompanied by strong east/southeast wind. The snowpack is now quite variable as evidenced in this MIN report from Saturday.

Loading from new snow and wind has made several persistent weak layers problematic over the past week. A combination of surface hoar and sun crust layers were buried on February 19 and currently sit 30-60 cm below the surface that seem to be most sensitive to human triggering at treeline elevations. 

A couple of weak layers that formed in January are buried in close proximity to one another 80-140 cm below the surface. Below that, an early season crust/facet layer lurks at the base of the snowpack.

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Conditions may have improved, but be mindful that deep instabilities are still present.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

Problems

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.