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Avalanche Forecast

Archived

Feb 26th, 2019–Feb 27th, 2019

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

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.

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

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.