Avalanche Forecast

Issued: Nov 23rd, 2013 8:25AM

The alpine rating is considerable, the treeline rating is moderate, and the below treeline rating is low. Known problems include Wind Slabs, Persistent Slabs and Loose Wet.

swerner, Avalanche Canada

Purcells.

Forecasts are based on limited observations. Dig down, test weak layers and keep an eye on rising temperatures.

Summary

Confidence

Fair - Due to the number of field observations

Weather Forecast

High pressure will strengthen though the forecast period bringing strong inversions (warmer temperatures) at upper elevations. No precipitation expected.Sunday/ Monday: A mix of sun and cloud. Alpine temperatures 0 degrees. Freezing levels near 2500 m. Ridgetop winds from the NW. Tuesday: Mainly sunny. Alpine temperatures below 0 degrees. Freezing levels falling to 1300 m. Ridgetop winds will be light from the NW.

Avalanche Summary

No recent avalanches reported. Earlier in the week a widespread cycle up to size 3 occurred throughout the region. Many of these avalanches ran on the October crust/ facet combo near the base of the snowpack.

Snowpack Summary

The average snowpack depths at upper elevations are near a metre or more. Wind slab problems likely exist on lee slopes.A bigger concern deeper in the snowpack is a melt-freeze / rain crust that formed early October. This is generally found from 70-120 cm down, with facetted (sugary) crystals above and below that are bonded poorly. The crust/ facet combo may be more predominant on Northerly aspects and allow for wider propagations, especially in places that have smooth ground cover (glacier ice, grassy slopes, rock slabs etc.).Snowpack conditions may change and deteriorate as temperatures rise in the alpine.

Problems

Wind Slabs

Recent winds have dominated alpine and treeline areas. Touchy wind slabs are likely found lee of terrain features.

Assess start zones carefully and use safe travel techniques.>Use caution in lee areas in the alpine and at treeline. Recent wind loading has created wind slabs.>

Aspects: North, North East, East, South East.

Elevations: Alpine, Treeline.

Likelihood

Possible - Likely

Expected Size

1 - 3

Persistent Slabs

Rider triggered slab avalanches are failing on a crust that sits 60-120 cm below the surface.

Dig down to find and test weak layers before committing to a line.>Be aware of the potential for large, avalanches due to the presence of buried crust/facet combo.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Loose Wet

Surface snow may become moist and weak with warm alpine temperatures and sunshine. Small loose wet avalanches could trigger the persistent weak layer buried deeper in the snowpack.

Minimize exposure to sun exposed slopes when things warm up. Indicators are moist surface snow, sluffing from trees, cliffs and steep southerly slopes.>

Aspects: North, North East, East.

Elevations: Alpine.

Likelihood

Possible - Likely

Expected Size

1 - 3

Valid until: Nov 24th, 2013 2:00PM