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Avalanche Forecast

Archived

Feb 23rd, 2019–Feb 24th, 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.

Wind slabs at upper elevations remain a concern. Persistent slabs at lower elevations still have a potential for human triggering.

Confidence

High - The weather pattern is stable

Weather Forecast

SUNDAY: Sunny with cloudy periods / light east wind / alpine temperature -19MONDAY: A mix of sun and cloud / light to moderate east wind / alpine temperature -20TUESDAY: A mix of sun and cloud / light northeast wind / alpine temperature -18

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. 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

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.