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Avalanche Forecast

Archived

Feb 28th, 2019–Mar 1st, 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.

Human triggered avalanches remain possible, especially in wind loaded areas and at lower elevations where buried surface hoar layers exist.

Confidence

Moderate - Due to the number of field observations

Weather Forecast

THURSDAY NIGHT - Cloudy with scattered flurries, 5 cm / southwest winds 10-20 km/h / alpine low temperature near -15FRIDAY - Mainly cloudy with isolated flurries / southeast winds 10-20 km/h / alpine high temperature near -18SATURDAY - Mainly sunny / east winds 10-15 km/h / alpine high temperature near -25SUNDAY - Sunny / northeast winds, 10-20 km/h / alpine high temperature near -17

Avalanche Summary

On Monday, size 1 wind slabs were reactive to human traffic. One size 2.5 natural wind slab avalanche likely occurred overnight Monday.Several size 2 wind slab avalanches were triggered with explosives 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 group ascended a steep slope near treeline. See the report here.

Snowpack Summary

Up to 15 cm of new snow and previous variable wind directions will mean that wind slabs can be found on all aspects at upper elevations.  Older wind slabs will be buried under the new snow and may be difficult to detect.A weak layer of facets (sugary snow) and surface hoar (feathery crystals) that was buried in mid January is down approximately 40-80 cm.  This layer is most prominent between 1600 m and 1900 m, but it has been found up to 2200 m in some areas. This weak layer may exist in combination with a crust on south facing slopes.  Recent snowpack tests and avalanche reports suggest that this layer remains reactive to human triggers.The bottom half of the snowpack is composed of weak, sugary facets.

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.