Avalanche Forecast

Issued: Mar 13th, 2017 4:50PM

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

Avalanche Canada shorton, Avalanche Canada

It's uncertain how the snowpack will respond to a warm, wet, windy storm. It's time to be extra conservative with your terrain choices.

Summary

Confidence

Moderate - Due to the number and quality of field observations

Weather Forecast

TUESDAY: Scattered flurries with 5-10 cm of snow, strong southwest winds, freezing level around 2000 m.WEDNESDAY: Wet flurries with 5-10 cm of snow, strong southwest winds, freezing level around 2200 m.THURSDAY: Morning flurries then clearing in the afternoon with freezing levels dropping to 1500 m and strong southwest winds.

Avalanche Summary

On Sunday, several large cornice triggered slabs were reported in the southeast part of the region (up to size 2.5) and ski cutting produced a few size 1 slabs in the latest storm snow. On Thursday, explosive avalanche control along the White River (in the northwest corner of the region) produced over 10 deep persistent slab avalanches releasing on basal facets. Most of the avalanches were size 3, including several than ran full path to valley bottom taking out mature forest and blocking the river with up to 8 m of debris. While these avalanches were triggered with explosives, warm temperatures or solar radiation can have a similar impact on deep weak layers.Expect a range of avalanche problems during the next few days of warm weather. Touchy wind slabs will form at higher elevations, unstable wet snow may exist at lower elevations, and the possibility of large persistent slab avalanches will remain.

Snowpack Summary

A warm, wet, and windy storm will form fresh wind slabs at higher elevations while rain with fall below treeline. March has delivered regular storms with roughly 50-90 cm of snow sitting above crust and facet interfaces from February. In some areas the snow above these interfaces may have a poor bond. The mid-pack in this region is generally strong, but the bottom third of the snowpack is composed of weak sugary facets roughly 1-1.5 metres deep. This remains a concern and should be on your radar, especially with the recent loading and ongoing warming.

Problems

Wind Slabs

An icon showing Wind Slabs
Steady snowfall and strong southwest winds are continuing to form touchy wind slabs in the lee of exposed terrain.
Use conservative route selection, choose moderate angled and supported terrain with low consequence.Be alert to conditions that change with elevation and time of day.Be cautious as you transition into wind affected terrain.

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

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2

Deep Persistent Slabs

An icon showing Deep Persistent Slabs
Storm loading and warming may increase the likelihood of triggering large deep persistent slab avalanches.
Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.Avoid steep convexities or areas with a thin or variable snowpack.Watch for clues, like sluffing off of cliffs, that the snowpack is warming up.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3

Valid until: Mar 14th, 2017 2:00PM