Avalanche Forecast South Rockies

Date Issued: Valid Until:

Avalanche Canada cgarritty, Avalanche Canada

Avalanche Forecast

Mon Feb. 11th ยท 4:53PM

Alpine

Danger Ratings Considerable

Treeline

Danger Ratings Considerable

Below Treeline

Danger Ratings Considerable
Storm Slabs Storm Slabs
Persistent Slabs Persistent Slabs
Deep Persistent Slabs Deep Persistent Slabs

Alpine

Danger Ratings High

Treeline

Danger Ratings High

Below Treeline

Danger Ratings Considerable

Alpine

Danger Ratings Considerable

Treeline

Danger Ratings Considerable

Below Treeline

Danger Ratings Moderate
The pieces are in place for a significant snowfall enhancement as the incoming storm collides with embedded arctic air. Avalanche danger will increase over the day as new snow accumulates and is affected by wind.

Confidence

Moderate - Forecast snowfall amounts are uncertain

Weather Forecast

Monday night: Increasing cloud with isolated flurries beginning with a trace of new snow. Light southwest winds, increasing to strong in the alpine.Tuesday: Cloudy with periods of snow bringing 20-30 cm of new snow, decreasing overnight. Light southwest winds, increasing to strong or extreme in the alpine. Alpine high temperatures around -11.Wednesday: A mix of sun and cloud with continuing isolated flurries and a trace of new snow. New snow totals up to 40 cm. Light west winds. Alpine high temperatures around -9.Thursday: Mainly cloudy with isolated flurries and a trace of new snow. Light southeast winds shifting to southwest in the evening. Alpine high temperatures around -7.

Avalanche Summary

A social media post from the Marten area of Elk Valley on Thursday describes touchy persistent slab conditions, with lots of smaller slabs releasing over the mid-January surface hoar layer. Check out the post here. Of note is the fact that this area was previously untracked, leaving the mid-January layer undisturbed. This is something to bear in mind as dry conditions persist and the motivation to step out of well-traveled terrain increases. Areas where this layer is undisturbed are far more likely to hold reactive persistent slabs.

Snowpack Summary

Forecast new snow will bury a variable surface of heavily wind affected old storm snow at alpine and wind-exposed treeline elevations, while adding to 25-35 cm of lower density storm snow from last week in sheltered areas above 1700 metres. In these sheltered areas, this older storm snow may cover a layer of weak, feathery surface hoar crystals. Below 1700 metres, the new snow will accumulate above a thinner cover (5-10 cm) of the same storm snow that instead overlies a melt-freeze crust.The mid-January layer of surface hoar or a crust is buried around 35 to 45 cm deep. The surface hoar is found on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m but has been found up to 2200 m. The melt-freeze crust is found on south aspects at all elevations. This layer was the subject of a recent Special Public Avalanche Warning.The middle of the snowpack is generally consolidated. The bottom half of the snowpack is unconsolidated and composed of weak and sugary faceted grains. The basal snowpack is becoming even weaker under prolonged cold temperatures, especially in thin snowpack areas.

Problems

Storm Slabs

Storm Slabs

New snow will be accumulating Monday night and over the day on Tuesday. It has the potential to quickly form reactive storm slabs in areas affected by wind. Loose dry avalanches will be an increasing concern as snow accumulates in sheltered areas.

If triggered, storm slabs may step down to deeper layers resulting in large avalanches.Avoid wind loaded pockets near ridge crests and roll-overs.Be cautious of sluffing in steep terrain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Very Likely - Likely

Expected Size

1 - 2
Persistent Slabs

Persistent Slabs

New snow will add load to a weak layer of surface hoar already buried 35-45 cm deep. This layer has been reactive to human triggers, particularly in undisturbed areas. It is best preserved in shaded, sheltered areas between 1600-2200 m.

Increase caution in open features at lower elevations, such as cutblocks, gullies, and cutbanks.Be aware of the potential for large avalanches due to the presence of buried surface hoar.Watch for signs of instability such as whumpfing, or cracking, especially from 1600-2200 m.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5
Deep Persistent Slabs

Deep Persistent Slabs

The bottom of the snowpack consists of weak and sugary faceted snow. The likelihood of triggering this layer may be relatively low, but the consequences remain high. Any deep persistent slab avalanche will be large and destructive.

Avoid steep, rocky terrain and shallow snowpack areas where triggering deep layers is more likely.Use conservative route selection, such as moderate-angled and smooth terrain with low consequence.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Unlikely

Expected Size

2 - 3