Avalanche Forecast

Issued: Feb 26th, 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 and wind-affected surfaces as you gain elevation. 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

TUESDAY NIGHT: Clear with cloudy periods. Alpine temperatures near -17C. Ridgetop winds 10-15 km/h from the northeast.WEDNESDAY: Sunny with cloudy periods. Alpine temperatures near -10C. Ridgetop winds 10-15 km/h from the east.THURSDAY: Mix of sun and cloud with isolated flurries, trace to 5 cm. Alpine temperatures near -14C. Ridgetop winds 10-15 km/h from the east-southeast.FRIDAY: Mainly cloudy with scattered flurries, trace to 5 cm. Alpine temperatures near -19C. Ridgetop winds 15-25 km/h from the east.

Avalanche Summary

On Monday, small (size 1) wind slabs were reactive to skier traffic.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 last 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.Also last 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

Moderate winds are smoothing alpine start zones and reverse loading lee terrain. Wind slabs exist in open, exposed areas at higher elevations and may be found on all aspects due to variable wind directions.Below this stack of wind-affected surfaces, a weak layer of surface hoar or faceted grains buried mid-January is down 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 bottom half of the snowpack is composed of weak and sugary faceted snow crystals.

Problems

Wind Slabs

Moderate to strong winds have scoured and smoothed alpine start zones and reverse loaded lee terrain. Expect to find wind slabs 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: East, South East, South, South West, West, North West.

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 27th, 2019 2:00PM