Avalanche Forecast

Archived

Mar 5th, 2021–Mar 6th, 2021

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, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

North Rockies.

Wind slabs are the primary avalanche problem but don't forget about deeper layers in shallow snowpack areas and in eastern areas of the region. Persistent layers are trickier to manage.

Confidence

Moderate - Uncertainties in both the snowpack structure and the weather forecast limit our confidence. Uncertainty is due to extremely variable snowpack conditions reported through the region.

Weather Forecast

Friday Night: Temperatures starting to cool. Trace to 5 cm snow. Strong SW winds continue.

Saturday: Wind veers toward the west and starts to ease (to moderate) late in the day. Trace to 10 cm snow. Overcast. Temperatures continue to cool with all elevations finally falling below freezing.

Sunday: Quieter pattern with southwest winds easing to light, treeline temperatures around -5 C, and little in the way of new snow.

Monday: Similar to Sunday but winds shifting to NW and increasing

Avalanche Summary

The warm temperatures this week triggered loose wet avalanches on solar (south throug west) aspects. Strong winds triggered wind slabs naturally up to size 2 and explosive controlled avalanche (near Pine Pass) up to size 3.

Snowpack Summary

We have a range of accumulated new snow totals since last weekend: somewhere around 90 cm in Pine Pass (the deepest), down to something like 30 or 40 cm in Kakwa. The key point is there's recent loose snow at higher elevations available for wind transport. Strong south to west winds in exposed areas have scoured some slopes and build windslabs on others. Freezing levels reaching treeline Thursday with +3 C at Renshaw, =8 C in Kakwa on the east side of the divide.

About a metre of snow covers a weak layer of facets (and potentially surface hoar) from mid February and a slightly deeper, widespread persistent weak layer from late January/early February that consists of surface hoar. It is most prevalent around treeline elevations, but likely reaches into the alpine and in openings below treeline too. These layers are both significantly shallower in the east of the region.

Terrain and Travel

Avoid freshly wind loaded terrain features.
Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.