Avalanche Forecast

Issued: Feb 24th, 2019 3:39PM

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

dsaly, Avalanche Canada

South Rockies.

Expect to find wind slabs at higher elevations on various aspects. Persistent slabs at lower elevations remain a concern and still have the potential for human triggering.

Summary

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

SUNDAY NIGHT: Clear. Alpine temperatures near -25C. Ridgetop winds light to moderate from the east.MONDAY: Mix of sun and cloud and isolated flurries in the evening, trace to 8 cm accumulating into Tuesday. Alpine temperatures near -22C. Ridgetop winds moderate from the east-northeast.TUESDAY: Mix of sun and cloud. Alpine temperatures near -24C. Ridgetop winds moderate from the northeast.WEDNESDAY: Sunny with cloudy periods. Alpine temperatures near -15C. Ridgetop winds light from the east-northeast.

Avalanche Summary

Several large (size 2) wind slabs were triggered with explosives control in the Castle area on Friday after a bout of strong to extreme southwest winds. Slab depths ranged from 20-60 cm.A MIN report from Grizzly Peak in the Elkford area on Thursday describes a persistent slab failing on the mid-January persistent weak layer as a ski touring group ascended a steeper slope near treeline. See the report here.On Thursday in adjacent Waterton National Park a recent large (size 2) deep persistent slab avalanche was observed. It occurred on a steep feature below treeline that was noted for its thin snowpack and for being reverse loaded by winds.

Snowpack Summary

Wind slabs exist in open, exposed areas at higher elevations. They may be found on all aspects due to variable wind directions. A weak layer of surface hoar or faceted grains buried mid-January is 50 to 80 cm below the surface. It is found on shaded and sheltered slopes and is most prominent between 1600 m and 1900 m but has been found up to 2200 m. It may overly a melt-freeze crust on south aspects. Recent avalanche reports and snowpack test results suggest that this layer remains reactive to human triggers.The bottom half of the snowpack is composed of weak and sugary faceted snow crystals.

Problems

Wind Slabs

Winds have shifted from southwest to easterly, new wind slabs may be found on a variety of aspects and cross-loaded features.

Use caution in freshly wind-loaded features, especially near ridge crests and in steep terrain.If triggered, wind slabs may step down to deeper layers resulting in large avalanches.Keep an eye out for reverse loading created by variable winds.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Persistent Slabs

A weak layer of surface hoar is buried around 50 to 80 cm, which is best preserved in shaded and sheltered areas between 1600 m and 1900 m.

Use added caution in open terrain features such as cutblocks, gullies and cutbanks.Be aware of the potential for wide propagation.

Aspects: All aspects.

Elevations: Treeline, Below Treeline.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 2.5

Valid until: Feb 25th, 2019 2:00PM