Avalanche Forecast

Issued: Nov 24th, 2013 8:20AM

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

swerner, Avalanche Canada

Purcells.

You need to be the detective. Dig down, test weak layers and watch rising alpine temperatures. Feel free to send your observations to forecaster@avalanche.ca.

Summary

Confidence

Poor - Due to the number of field observations

Weather Forecast

An upper ridge of high pressure will remain over the Interior regions. At higher elevations (1600-2800m) an above freezing layer will persist through Tuesday and be pushed out by Wednesday. Monday: Mix of sun and cloud. Alpine temperatures near 0 degrees. Freezing levels rising to 2600 m. Light-moderate ridgetop winds from the West. Tuesday: Mix of sun and cloud. Alpine temperatures -1. Freezing levels 2000 m. Light westerly ridgetop winds.Wednesday: Mainly sunny. Alpine temperatures -5. Freezing levels dropping to 1500 m. Light westerly winds.

Avalanche Summary

No recent avalanche activity has been reported. The weight of a person easily triggered persistent slab problems last week. The likelihood of triggering may be decreasing, however the consequences would be huge.

Snowpack Summary

The average snowpack depths at treeline sit 70-100 cm and near a metre or more in the alpine. A surface hoar layer has been found in the Columbias 60-120 cm down and seems to be spotty, and drainage specific. I'm not sure if it exists in the Purcells. Have you seen any? Deeper in the snowpack near the base is a melt-freeze / rain crust that formed in October. This is generally found 70-110 cm down, with facetted (sugary) crystals above and below that are poorly bonded. 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 if temperatures rise in the alpine.

Problems

Wind Slabs

Recent ridgetop winds have formed wind slabs on the lee of terrain features and slopes.

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

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

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Persistent Slabs

The probability of triggering a persistent slab may be decreasing; however if triggered, the consequence would be high. Watch shallower, thin-spot trigger points.

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

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 5

Valid until: Nov 25th, 2013 2:00PM