Avalanche Forecast

Issued: Mar 16th, 2019 6:47PM

The alpine rating is high, the treeline rating is considerable, and the below treeline rating is considerable. Known problems include Wind Slabs, Loose Dry and Loose Wet.

Tim Haggarty, Parks Canada

Banff Yoho Kootenay.

Watch for solar heating to weaken the snowpack Sunday with a rise in the freezing levels to follow. Surface slabs and sluffs have been serious enough in the last several days... there is significant uncertainty as to how deeper weak layers will react

Summary

Weather Forecast

Despite a stiff breeze and thin cloud Saturday, solar heating was strong. Sunday will dawn clear and winds will likely diminish: expect a significant solar shock to the snowpack. This begins a significant warming trend that will bring freezing levels to 3000m later in the week. Both size and likelihood of avalanches are expected to increase.

Snowpack Summary

15- 50cm has accumulated since March 7. Modertate to strong SW-W winds have redistributed this snow treeline and above. This snow sits over previous widespread wind effect in the alpine, suncrusts on steep S aspects and 30-50cm of sugary facets everywhere else. While a tough midpack exists in thicker areas, facets to ground are seen in many others.

Avalanche Summary

Several Natural (eg 1, 2) and human triggered eg (1, 2) slabs have been seen over the last two days. South aspects have been the most active: increased sensitivity due to solar heating, buried crusts, and slab formation due to rapid settlement are all likely factors here. Loose wet activity also started up at around 15:00 as solar heating peaked.

Confidence

Timing or intensity of solar radiation is uncertain on Sunday

Problems

Wind Slabs

Strong SW-W winds have built wind slabs in open areas above treeline. In may cases, these slabs initiate a larger loose dry avalanche as they run. In a few examples these slides have gouged to the deep persistent layers near the base of the snowpack

Watch for surface cracking and stiffer surface layers of snow.Even small avalanches may run a long ways under the current conditions.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2.5

Loose Dry

The faceted snow is easily initiated as a sluff in steep terrain that will entrain all available loose snow until it hits lower angled terrain. If a windslab or cornice initiates these, expect increased width, mass, momentum and reach.

Good group management is essential to manage current conditions safely.Use caution above cliffs and terrain traps where small avalanches may have severe consequences.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Loose Wet

While moist snow avalanches will start to become a problem themselves at lower elevations, as solar heating starts to take hold, consider a wider range of possible triggers to be available for the avalanche problems at upper elevations as well.

Be alert to conditions that change with elevation.Pay attention to overhead hazards like cornices which could trigger slabs or larger sluffs.

Aspects: East, South East, South, South West, West.

Elevations: All elevations.

Likelihood

Very Likely

Expected Size

1 - 2

Valid until: Mar 17th, 2019 4:00PM