Archived

Avalanche Forecast

Dec 18th, 2018–Dec 19th, 2018

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

3: Considerable

The avalanche danger rating below treeline will be considerable

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Alpine

3: Considerable

The avalanche danger rating in the alpine will be considerable

Treeline

3: Considerable

The avalanche danger rating at treeline will be considerable

Below Treeline

2: Moderate

The avalanche danger rating below treeline will be moderate

Regions: South Rockies.

New snow has pushed the snowpack past it's tipping point, leaving it primed for human triggering. Conservative terrain choices are recommended.

Confidence

Moderate -

Weather Forecast

TUESDAY NIGHT: Lingering flurries could produce another 5cm of snow, strong wind from the west, freezing level dropping to 1100m, alpine temperatures drop to -8c. WEDNESDAY: Mix of sun and cloud with isolated flurries, strong wind from the west, freezing level up to 1400m, alpine high temperatures around -5c. THURSDAY: Increasing cloud with stormy weather starting in the evening, moderate wind from the west increasing throughout the day, freezing level climbs to 1500 m throughout the day, alpine high temperature around -5c. FRIDAY: 5-10cm of snow by the morning then cooling and clearing throughout the day, moderate to strong wind from the northwest, freezing level drops to valley bottom, alpine high temperatures around -10c.

Avalanche Summary

Widespread natural activity was observed around Elkford and Sparwood on Tuesday. Many avalanches failed on deep persistent weak layers in the alpine.Snowmobiles remotely triggered several small avalanches on cutbanks north of Sparwood. Although these avalanches were small, they involved the entire depth snowpack and failed weak layers at the bottom of the snowpack. See this MIN report. Deep persistent slabs were also reactive over the past few days. On Monday, a skier triggered a large slab avalanche (size 2) on a east aspect around 1800 m. The avalanche failed on a persistent weak layer 40 cm below the surface. On Friday and Saturday, explosive control produced numerous large (size 2-3) wind slab and deep persistent slab avalanches on north and east aspects above 2000 m.

Snowpack Summary

Tuesday's storm hit the region with 20-40 cm of new snow, forming fresh storm slabs at upper elevations. This substantially increases snowpack depths throughout the region, which prior to the storm range from 30-120 cm in the alpine and much less at lower elevations.The lower snowpack has a weak structure composed of facets and crusts, and the additional load of the new snow has pushed these weak layers past the tipping point. Any avalanche could step down to the bottom of the snowpack.

Avalanche Problems

Deep Persistent Slabs

Any avalanche in the upper snowpack will likely step down to the weak snow at the bottom of the snowpack and produce large full depth avalanches.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Back off if you encounter signs of instability like whumphing, shooting cracks or recent avalanches.Minimize overhead exposure; avalanches may reach the end of run out zones.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1.5 - 2.5

Storm Slabs

20-40 cm of new snow has left storm slabs primed for human triggering, especially on steep and wind loaded slopes.

Avoid freshly wind loaded features.If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Possible - Likely

Expected Size: 1 - 2