Archived

Avalanche Forecast

Mar 4th, 2017–Mar 5th, 2017

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

2: Moderate

The avalanche danger rating at treeline will be moderate

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

2: Moderate

The avalanche danger rating at treeline will be moderate

Below Treeline

1: Low

The avalanche danger rating below treeline will be low

Regions: South Rockies.

A week of heavy snowfall and strong winds have left large storm slabs primed for human triggering. Avoid overhead hazards and stick to mellow terrain.

Confidence

Moderate - Wind speed and direction is uncertain

Weather Forecast

SUNDAY: Light snow with up to 5 cm accumulations in the afternoon, moderate southwest winds, alpine temperatures around -10 C.MONDAY: Cloudy with isolated flurries, strong southwest winds, alpine temperatures around -12 C.TUESDAY: Cloudy with isolated flurries, strong southwest winds, alpine temperatures around -10 C.

Avalanche Summary

On Saturday, several size 2 natural storm slabs were reported in alpine terrain and explosive control and ski cutting produced size 1-1.5 avalanches at treeline and in the alpine. On Thursday, a size 2.5 deep persistent slab avalanche was reported from the Elkford-North riding area. It was from approximately 2500 m on a SE aspect. It looked to be 24 hrs old and likely failed earlier in the storm. It failed within the basal facets (deep persistent slab) and scrubbed down to rocks.Natural activity is expected to taper off, but storm slabs will remain primed for human triggering.

Snowpack Summary

Another 15 cm of new snow on Friday brings the three day total to 20-30 cm and the total from the past week to 40-80 cm. Strong southwesterly winds have redistributed the new snow onto leeward slopes, building thicker and stiffer slabs. The new snow will likely have a poor bond to the old snow interface that consists of stiff wind slabs, crusts, and facets. The mid-pack in this region is generally strong, but the bottom third of the snowpack is composed of weak facets (sugary snow crystals). Approximately 100-120 cm of settled snow sits above this weak layer of sugary, rotten facets that developed in December. This remains a concern and should be on your radar, especially with the recent loading from snow and wind.

Avalanche Problems

Storm Slabs

Storm slabs are primed for rider triggering, especially on leeward slopes and behind terrain features that are wind loaded.

Use conservative route selection, choose moderate angled and supported terrain with low consequence.Use caution in lee areas in the alpine and treeline. Storm snow is forming touchy slabs.The new snow will require several days to settle and stabilize.

Aspects: All aspects.

Elevations: All elevations.

Likelihood: Likely

Expected Size: 1 - 2

Deep Persistent Slabs

A weak layer near the base of the snowpack has the potential for large avalanches, especially in areas with minimal rider compaction or thin variable snow cover.

Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.Be aware of the potential for full depth avalanches due to weak layers at the base of the snowpack.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood: Possible

Expected Size: 2 - 4