Avalanche Forecast

Issued: Mar 9th, 2017 4:26PM

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

cam_c, Avalanche Canada

South Columbia.

Snow and wind will drive the danger up for Friday, then warming and sun-exposure, coupled with the potential for cornice triggers, will increase the likelihood of massive deep persistent slabs for the weekend.

Summary

Confidence

Moderate - Freezing levels are uncertain on Saturday

Weather Forecast

FRIDAY: Cloudy with 15-20cm of fresh snow accompanied by moderate SW winds. Freezing levels as high as 1500m for southern areas, but remaining near valley bottoms in the north.SATURDAY: A mix of sun and cloud with localized periods of intense sun-exposure and isolated light flurries. Light to moderate SW winds. Freezing levels again rising to 1500m for southern areas, but remaining near valley bottoms in the north.SUNDAY: Cloudy with 5-10cm of fresh snow, light westerly winds and freezing levels again rising to 1500m for southern areas, but remaining near valley bottoms in the north.

Avalanche Summary

Reports from Tuesday and Wednesday include numerous natural dry loose avalanches up to Size 2.5 in steep terrain. A few natural wind slab avalanches up to Size 2.5 were also reported, one triggered by a cornice fall. Skier and explosives control also produced 15-60cm thick storm and wind slab avalanches up to Size 1.5. On Sunday and Monday we had reports of two very large natural deep persistent slab avalanches in the Selkirk mountains near Trout Lake. One was a 250 cm deep Size 3 on a north aspect on Sunday and the other was a 300 cm deep Size 4 on a southwest aspect on Monday that filled the creek at the bottom of the valley and ran 100m up the other side, both of which released on deeply buried old facets.

Snowpack Summary

Around 60-100cm of settled storm snow from the past week is bonding poorly to faceted snow, thin sun crust on steep southerly aspects, as well as more isolated small buried surface hoar. Southerly winds have formed touchy slabs at all elevations with multiple weaknesses within and under this recent storm snow. A persistent weakness buried mid-February is now down about 90-135cm and 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.

Problems

Storm Slabs

Weaknesses within the recent storm snow are susceptible to human triggering. These storm slabs are particularly deep and touchy on slopes loaded by southerly winds and have the potential to step down to deeper persistent weaknesses.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 3

Persistent Slabs

Various persistent weaknesses strewn throughout the snowpack create the potential for large step-down avalanches. Warming and sun-exposure is expected increase the likelihood of these massive avalanches, especially with cornice-fall triggers.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

2 - 4

Valid until: Mar 10th, 2017 2:00PM