Avalanche Forecast

Issued: Feb 22nd, 2019 5:20PM

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.

cgarritty, Avalanche Canada

South Rockies.

New snow will be adding to our wind slab problems at upper elevations over Friday night. Meanwhile, riders can still trigger persistent weak layers at lower elevations. Terrain like cutblocks, steep forest openings, and gullies remain suspect.

Summary

Confidence

Moderate -

Weather Forecast

Friday night: Mainly cloudy with scattered flurries bringing a trace to 5 cm of new snow. Light to moderate southwest winds.Saturday: Mainly cloudy with isolated flurries and a trace of new snow. Light to moderate northeast winds. Alpine high temperatures around -16.Sunday: Sunny with cloudy periods. Light variable winds. Alpine high temperatures around -18.Monday: Cloudy with sunny periods. Light to moderate east winds increasing over the day. Alpine high temperatures around -15.

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: LINK 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. In sheltered terrain, around 20 to 30 cm of recent soft snowfall may be found.The mid-January weak layer of surface hoar or faceted grains is buried around 50 to 80 cm. 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 middle of the snowpack is generally consolidated. The bottom half of the snowpack is unconsolidated and composed of weak and sugary faceted grains. There is potential for shallower avalanches to step down to these deeper weak layers.

Problems

Wind Slabs

Light new snow amounts will be resupplying our already active wind slab problem over Friday night. Winds are set to shift from southwest to east, so touchy new slabs may be expected on a variety of aspects.

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 - Likely

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

Possible

Expected Size

1.5 - 2.5

Valid until: Feb 23rd, 2019 2:00PM