Avalanche Forecast

Issued: Feb 24th, 2018 4:52PM

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

pgoddard, Avalanche Canada

South Rockies.

Touchy wind slabs can be triggered by the weight of a person or snowmobile.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

SUNDAY: ~5 cm light dry snow. Freezing level near 1000 m. Moderate to strong south-westerly winds.MONDAY: Mix of sun and cloud. Freezing level near 700 m. Moderate west to north-westerly winds. TUESDAY: 5-10 cm snow. Freezing level near 1000 m. Moderate to strong south-westerly winds.More details can be found in the Mountain Weather Forecast.

Avalanche Summary

Snowmobilers triggered size 1.5 and size 2 wind slabs in the Crowsnest area on Saturday. On Friday, evidence of a persistent slab avalanche cycle from earlier in the week was observed near Mear Lake.On Thursday, observations of some very large slabs were made in the North Elk valley. These are thought to have failed within the last week. Whumpfing was reported at treeline in the North Elk valley as well.It is still possible to trigger a surprisingly large wind slab or persistent slab with the weight of a person or sled, especially from a convexity or thin snowpack area.

Snowpack Summary

Touchy new wind slabs were found on Saturday in the Crowsnest area. These are expected to continue to build over the next few days. Fragile cornices and hard and soft wind slabs can be found on many alpine and treeline slopes. Wind slabs overlie various surfaces, including older hard wind slabs, crusts, facets and spotty surface hoar.The lower snowpack is weak with two primary concerns:1) A widespread weak layer from mid-December composed of facets, crusts, and surface hoar that is 100-150 cm deep.2) A rain crust with sugary facets buried in late November near the bottom of the snowpack.Although the snowpack structure is variable across the region, these persistent weak layers are generally widespread.

Problems

Wind Slabs

Touchy wind slabs may be found on a variety of slopes at and above treeline.

If triggered, the wind slabs may step down to deeper layers, resulting in large avalanchesBe cautious as you transition into wind affected terrain.Avoid steep slopes below cornices.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Likely

Expected Size

1 - 2.5

Deep Persistent Slabs

Deeply buried weak layers are most likely to be triggered from thin or variable snowpack areas; or with a large load, like a cornice fall.

Avoid steep convexities or areas with a thin or variable snowpack.Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 3.5

Valid until: Feb 25th, 2018 2:00PM