Avalanche Forecast

Issued: Feb 22nd, 2018 4:30PM

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

pgoddard, Avalanche Canada

South Rockies.

Strong forecast winds will continue to build wind slabs, which overlie a fundamentally weak snowpack in many areas.

Summary

Confidence

Moderate - Due to the number of field observations

Weather Forecast

FRIDAY: Mix of sun and cloud with possible flurries. Freezing level at valley floor. Moderate to strong westerly winds.SATURDAY: Mainly sunny. Freezing level at valley floor. Moderate westerly winds.SUNDAY: Mainly sunny. Freezing level near 700 m. Moderate to strong north-westerly winds.More details can be found in the Mountain Weather Forecast.

Avalanche Summary

It has been fairly quiet the last couple of days, however 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, especially from a convexity or thin snowpack area. If the sun is shining, avoid exposure to steep solar aspects where loose wet avalanche activity is possible.

Snowpack Summary

You are likely to find variable surfaces in open terrain after recent strong winds took out their fury on the upper snowpack. Fragile cornices and hard and soft wind slabs can be found on many alpine and treeline slopes. Ongoing strong winds are expected to keep building wind slabs. A crust/surface hoar interface is about 40-60 cm down, but little is known about its sensitivity and distribution.The lower snowpack in this region 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

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

Unlikely - Possible

Expected Size

2 - 4

Valid until: Feb 23rd, 2018 2:00PM