Avalanche Forecast

Archived

Mar 3rd, 2020–Mar 4th, 2020

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural and human triggered avalanches likely.

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

South Coast.

The seemingly continuous storm cycle continues, with snowfall and strong wind Tuesday night. Wind slabs will form and the snow will continue to load a buried weak layer, where it exists. Sunny skies on Wednesday may rapidly deteriorate the snow on sun-exposed aspects.

Confidence

Moderate - Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

TUESDAY NIGHT: Cloudy with snowfall, accumulation 5 to 15 cm, strong west wind, treeline temperature -3 C, freezing level 1000 m dropping to 600 m.

WEDNESDAY: Mix of sun and cloud, light west wind, treeline temperature -4 C, freezing level 800 m.

THURSDAY: Cloudy with snowfall, accumulation 15 to 30 cm, strong southwest wind, treeline temperature -3 C, freezing level 900 m.

FRIDAY: Mix of sun and cloud with isolated flurries, accumulation 5 cm, light southwest wind, treeline temperature -5 C, freezing level 600 m.

Avalanche Summary

On Tuesday morning, tree bombs, pinwheeling, and small loose dry avalanches were observed. They all occurred naturally and likely failed in the storm snow from Monday night.

Snowpack Summary

The next storm on Tuesday night will drop around 10 cm of snow across the region, followed by some sunny skies. The snow may moisten on sun-exposed slopes but stay dry on shaded slopes. The wind will be strong from the west during the storm, so expect wind slab development in lee terrain features, particularly near ridges.

In some of the region, around 50 to 80 cm of snow overlies a layer of surface hoar on north-facing aspects near and above treeline. The layer has been found to be reactive snowpack tests, such as in this MIN and this MIN. This persistent weak layer warrants investigation and a conservative terrain use strategy. Check out the latest forecaster blog that offers a deeper dive into these conditions.

The remainder of the snowpack is well-settled. The snowpack depth varies from around 250 to 300 cm at the peaks of the North Shore mountains (1400 m), tapering rapidly with elevation.

Terrain and Travel

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Minimize exposure to sun-exposed slopes when the solar radiation is strong.
Be aware of the potential for large avalanches due to the presence of buried surface hoar.

Problems

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.

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.