Avalanche Forecast

Issued: Mar 18th, 2017 3:44PM

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

cgarritty, Avalanche Canada

South Rockies.

The sun will be out in full force on Sunday. There is no reason to expect a rapid drop in avalanche danger.

Summary

Confidence

Moderate -

Weather Forecast

Sunday: Sunny with cloudy periods. Moderate to strong west winds. Freezing level to 1400 metres with alpine temperatures around -9. Monday: A mix of sun and cloud. Light east winds. Freezing level to 1500 metres with alpine temperatures around -8. Tuesday: Mainly cloudy with isolated flurries and a trace of new snow. Light south winds. Freezing level to 2000 metres with alpine temperatures around 0.

Avalanche Summary

A report from Friday in the Crowsnest area showed a natural Size 3.5 deep persistent slab that began as a ridgetop wind slab release before stepping down to ground as it descended its track. Another explosives triggered Size 3.5 deep persistent slab was reported north of Sparwood. The resulting debris pile appears to be roughly 10 metres high.Looking forward, recently formed wind slabs at high alpine elevations will likely be reactive to human triggering on Sunday. The emergence of the sun will promote both natural avalanche activity and human triggering potential. Although cooling temperatures should gradually reduce the likelihood of persistent slab avalanches at lower elevations over the coming days, the scale of recent persistent slab activity warrants being very cautious with that assumption.

Snowpack Summary

Light new snow accumulations over Thursday and Friday have been redistributed into touchy wind slabs in alpine terrain while rain has soaked the snowpack at treeline and below, breaking down a recently formed rain crust at lower elevations. Below the new snow and crust, regular snowfall throughout early March saw roughly 50-90 cm of snow accumulate above the crust and facet interfaces from February. In some areas this storm snow may have a poor bond to these interfaces. Aside from that uncertainty, the mid-pack in the region is generally strong. With that said, the bottom third of the snowpack is composed of weak sugary facets roughly 1-1.5 metres deep. The potential for full-depth avalanches over this basal weakness remains a real concern, especially as ongoing loading and warm temperatures continue to stress the snowpack.

Problems

Deep Persistent Slabs

Be careful not to overestimate the stabilizing effect of cooling temperatures on Sunday. Rain has saturated the snowpack with warmth and deep persistent slabs still have the potential to release naturally or with a sufficient trigger on Sunday.

Recognize and avoid avalanche runout zones.Wind slabs, cornices or the weight of a rider may trigger deep layers and result in large avalanchesAvoid exposure to overhead hazards when solar radiation is strong.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Wind Slabs

All the rain that soaked lower elevations fell as snow above about 2000 metres. Expect touchy new wind slabs that thicken with elevation in the alpine and be aware that they are an overhead hazard to lower elevations, especially when the sun is out.

Be alert to conditions that change with elevation and aspect.If triggered, wind slabs may step down to deeper layers and result in large avalanches.Minimize exposure to sun exposed slopes when solar radiation is strong.

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

Elevations: Alpine.

Likelihood

Likely - Very Likely

Expected Size

1 - 2

Valid until: Mar 19th, 2017 2:00PM