Avalanche Forecast

Issued: Mar 6th, 2017 4:02PM

The alpine rating is considerable, the treeline rating is considerable, and the below treeline rating is moderate. Known problems include Storm Slabs and Persistent Slabs.

triley, Avalanche Canada

South Columbia.

Storm slabs continue to be a concern for human triggering. This problem is more likely where a persistent weak layer of facets and/or a crust is sitting beneath the storm snow.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Overnight: Unsettled with convective flurries resulting in 5-10 cm in some areas combined with moderate westerly winds and alpine temperatures around -15. Tuesday: A mix of sun and cloud with convective flurries and light southwest winds. Wednesday: Overcast with light snow and periods of heavy flurries combined with light southwest winds. Thursday: A mix of sun and cloud with flurries during the day, and a stronger system moving in late in the day.

Avalanche Summary

On Sunday we had reports of storm slab avalanches releasing naturally, with explosives control, and by pushing snow with a snowcat up to size 2.0. There was also a deeper release 250 cm down, suspected to have released on buried facets that resulted in a size 3.0 avalanche in the Selkirk mountains near Trout Lake. On Saturday we had reports of widespread storm slab activity.

Snowpack Summary

Just under a week of stormy weather has delivered a wide-ranging 65-120 cm of new snow to the region. Moderate to strong southerly winds accompanied the new snow, promoting touchy storm slab formation at all elevations. The new snow has buried widespread faceted surface snow, thin sun crust on steep solar aspects, as well as more isolated surface hoar to 4mm. About 90-135cm below the surface you'll find the mid-February interface which is composed of a thick rain crust up to about 1800 m, sun crusts on steep solar aspects, and spotty surface hoar on shaded aspects. This layer has seen a recent increase in more sudden snowpack test results and has been identified as a failure plane in a number of recent avalanches. Its reactivity has been especially prominent over the crust at lower elevations. Any continuing activity at this interface will likely see it emerge as a persistent weak layer.

Problems

Storm Slabs

Storm slabs continue to be a concern for human triggering. Storm slabs may take a few days to settle and bond to the old surface, especially where the wind has transported snow into deep pockets.

Be increasingly cautious as you transition into wind affected terrain.Be alert to conditions that change with elevation.The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Persistent Slabs

Storm slabs may take longer to settle and bond where they are sitting on a crust and/or a layer of facets that grew during the latest cold clear weather. Fracture propagations may be long resulting in large and dangerous avalanches.

Watch for whumpfing, hollow sounds, and shooting cracks.Be aware of the potential for wide propagations.Use conservative route selection, choose moderate angled and supported terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Valid until: Mar 7th, 2017 2:00PM