Avalanche Forecast

Archived

Mar 5th, 2020–Mar 6th, 2020

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 unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

South Coast.

Slabs that formed on Thursday may take a bit more time to stabilize. Watch out on sun-exposed slopes during periods of intense sun. Cornices are expected to be large and weak.

Confidence

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

Weather Forecast

THURSDAY NIGHT: Cloudy with snowfall then clearing, accumulation 5 cm, moderate southwest wind, treeline temperature -4 C, freezing level 600 m.

FRIDAY: Mix of sun and cloud, light southwest wind, treeline temperature -5 C, freezing level 800 m.

SATURDAY: Early-morning snowfall then a mix of sun and cloud, accumulation 5 to 10 cm, light southwest wind, treeline temperature -5 C, freezing level 600 m.

SUNDAY: Mostly clear skies, light northwest wind, treeline temperature -4 C, freezing level 800 m.

Avalanche Summary

No new avalanches were observed on Wednesday. Although we do not yet have observations from Thursday, it is expected that many avalanches occurred within the storm snow and potentially the surface hoar layer described in the Snowpack Summary. Natural avalanche activity should quiet down on Friday, but human-triggering will remain likely.

Snowpack Summary

Thursday's storm dropped around 20 to 30 cm of snow across the region. The snow fell with strong south to southwest wind, forming wind slabs in lee terrain features.

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 in 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 300 to 400 cm at the peaks of the North Shore mountains (1400 m), tapering rapidly with elevation, with no snow below 700 m.

Terrain and Travel

Continue to make conservative terrain choices while the storm snow settles and stabilizes.
Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Be aware of the potential for large avalanches due to the presence of buried surface hoar.
Surface hoar distribution is highly variable. Avoid generalizing your observations.
Minimize your exposure time below cornices.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-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.