Avalanche Forecast

Issued: Feb 4th, 2015 8:36AM

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

triley, Avalanche Canada

Purcells.

If more snow than forecast arrives during the day on Thursday, avalanche danger may reach HIGH.

Summary

Confidence

Fair - Timing, track, or intensity of incoming weather system is uncertain

Weather Forecast

Snow starting on Thursday with 5-10 cm expected during the day combined with moderate Southwest winds and alpine temperatures around -5. Snow and moderate wind continuing on Friday with another 5-10 cm forecast during the day and a further 10-15 cm overnight when the winds become strong Southwest and the freezing levels climb up to about 2000 metres. The North of the region may be cooler as the bulk of the warm air should be deflected to the Southeast by the cold arctic air that is sitting on the Eastern side of the Rockies. The storm should continue on Saturday with another pulse of 10-15 cm of snow and strong Southerly winds pushed into the region from the coast.

Avalanche Summary

Several natural and skier controlled avalanches up to size 1.5 mostly on North or Northeast aspects. There were a couple of remotely triggered avalanches up to size 2.0 that released down about 40 cm above the end of January crust. There was one skier accidental size 2.0 (reported yesterday as size 1.5) on a Northeast aspect in the alpine that released down 40-60 cm on the mid-January surface hoar (3.0 mm).

Snowpack Summary

A thin layer of new storm snow (10-20 cm)has fallen on a variety of old surfaces, including hard crusts, breakable crusts at higher elevations, and surface hoar in some areas. A melt freeze crust can be found up to about 2200m. At higher elevations, the surface is heavily wind affected. The depth of the mid-January surface hoar is highly variable across the region and it may have been destroyed by warmth at low elevations. Where it does exist, it can be found between 30 and 70 cm below the surface. The mid-December surface hoar layer lies below a strong mid-pack down about 60 to 120cm. Both of these persistent layers have been reactive recently. The mid-November weak layer of crusts and facets can still be found near the bottom of the snowpack. It has been unreactive lately, but should be on your radar in shallow snowpack areas where there is more chance of triggering.

Problems

Storm Slabs

Forecast new snow and wind are expected to result in natural avalanches releasing within the storm slab, or on the buried crust. Incremental loading from several pulses of moisture may make it difficult to forecast the timing of natural avalanches.

Use ridges or ribs to avoid pockets of wind loaded snow.>Minimize exposure during periods of heavy loading from new snow, wind.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 3

Persistent Slabs

Buried persistent weak layers may be over-loaded by the forecast new storm snow resulting in human triggering, or storm slab avalanches in motion stepping down to the deeply buried weak layers.

Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.>Be aware of the potential for large, deep avalanches due to the presence of buried surface hoar.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

2 - 4

Deep Persistent Slabs

Deeply buried weak layers may react to large loads like an avalanche in motion, or could be triggered by light loads in thin and variable snowpack areas.

Stay clear of thin areas that may propagate to deeper instabilities.>Pay attention to overhead hazards like cornices.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Unlikely

Expected Size

3 - 6

Valid until: Feb 5th, 2015 2:00PM