Avalanche Forecast

Issued: Apr 1st, 2017 4:37PM

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

cgarritty, Avalanche Canada

Cariboos.

A final pulse of wind and light snowfall will see wind slabs and cornices continue to grow over Saturday night. The potential for a large wind slab or cornice release to trigger a deeper persistent slab can't be discounted yet.

Summary

Confidence

Moderate -

Weather Forecast

Saturday night: Scattered flurries bringing about 5 cm of new snow. Moderate west winds.Sunday: Mainly cloudy with isolated flurries and a trace of new snow. Moderate northwest winds. Freezing level to 1300 metres with alpine temperatures around -8.Monday: A mix of sun and cloud. Light west winds. Freezing level to 1500 metres with alpine temperatures around -6.Tuesday: Cloudy with sunny periods. Light to moderate southeast winds. Freezing level to 1800 metres with alpine temperatures around -4.

Avalanche Summary

Reports from Friday included observations of numerous loose snow releases to Size 1.5 occurring with solar warming near Blue River. Improved visibility also allowed for observations of recent (up to 72 hours old) slab avalanche activity reaching up to Size 4 in the same area. The largest of these avalanches are certain to have failed on deeply buried persistent weak layers.Reports from Thursday included observations of two large (Size 2.5 and Size 3) storm slabs releasing naturally from steep alpine terrain north of Blue River. Crown fractures of these slides ranged from 60-80 cm. Extensive natural sluffing to Size 2 was also observed, with loose dry activity on northerly aspects and loose wet from solar aspects. One Size 1 cornice fall was also reported.

Snowpack Summary

Up to 40 cm of recent storm snow has fallen at upper elevations. The new snow is dry up high and moist at 1800 m and below. This now brings 40-90 cm of accumulated snow which overlies a rain crust below 2000 m or a sun crust on solar aspects at higher elevations. New wind slabs are developing on leeward slopes and behind terrain features and large, fragile cornices exist along ridgelines. At higher elevations, the February weak layers are down 120-150 cm and woke up during last week's storm with many avalanches stepping down to them. The deep mid-December facet layer and November rain crust both still linger near the bottom of the snowpack and a few avalanches and cornice falls have also stepped down to these layers last week resulting in some very large full depth avalanches. These layers remain a real concern while more reactive wind slabs and cornices continue to present the risk of acting as triggers for deeper weaknesses.

Problems

Wind Slabs

Recent southwest winds have redistributed storm snow in exposed terrain at higher elevations, forming large wind slabs. These slabs may remain reactive to human triggering on Sunday.

Use ridges or ribs to avoid pockets of wind loaded snow.Look for patterns of wind loading and avoid traveling near thinner edges of wind slabs.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

A cornice fall or smaller slab avalanches could trigger large, destructive avalanches on deeply buried weak layers. There is a low likelihood of triggering but a high consequence if triggered. These avalanches would likely run full path.

Avoid lingering in runout zones.If triggered, wind slabs or cornices may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely - Possible

Expected Size

2 - 4

Cornices

Recent warm, wet, and windy weather has been contributing to cornice growth. Even a small cornice release has the potential to trigger a slab avalanche below it. Cornices become weak with daytime warming and/or sun exposure.

Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.

Aspects: North, North East, East, South East, South.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Apr 2nd, 2017 2:00PM