Avalanche Forecast

Issued: Feb 23rd, 2016 8:50AM

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

rbuhler, Avalanche Canada

Purcells.

Sun exposure and afternoon warming will maintain the potential for large destructive avalanches. Conservative terrain choices with low overhead exposure are essential.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

A ridge of high pressure dominates for the next several days. A mix of sun and cloud is expected on Wednesday with light alpine winds from the west. Freezing levels are expected to drop below valley bottom overnight and reach around 1500m in the afternoon. Mostly sunny conditions are expected for Thursday with light westerly winds and freezing levels reaching around 1800m in the afternoon. Mostly sunny conditions are expected on Friday with moderate southwest winds in the alpine and freezing levels reaching well over 2000m.

Avalanche Summary

On Monday, a few size 1 ski cuts were reported from steep convex features. These were on an east aspect at treeline and were 20-40cm thick. Skier triggered sluffing from steep terrain features below treeline was also reported. Reports from Sunday include a natural Size 2 persistent slab avalanche and a Size 2.5 cornice failure. Several Size 1 skier-triggered wind slabs were also reported and explosives control produced slab avalanches up to Size 3. On Saturday one person was killed and another was hospitalized in a large avalanche in the Quartz Creek area west of Golden. This size 3 snowmobile-triggered slab avalanche occurred on a S-SW aspect in the alpine and is suspected to have released on the Feb. 12 interface.

Snowpack Summary

20-30 cm of snow in the past few days has added to the recent storm slab bonding reasonably well to a crust 40-60 cm below the surface, that was buried on February 12th. However, in isolated areas (such as shady sheltered treeline slopes) there may be a weak layer of surface hoar at the storm snow/crust interface that is touchy to human triggers and may result in wide propagations. The early January surface hoar/ facet layer is typically down 70-120 cm. Avalanche activity at this interface has tapered-off over the past week, but I'd be reluctant to trust this potentially destructive layer just yet. In general, the lower snowpack is well settled and strong, apart from some thin snowpack areas where basal facets exist.

Problems

Persistent Slabs

A weak layer of surface hoar and/or crust down 70-90cm is susceptible to large triggers such as cornice falls or smaller avalanches stepping down. Wide fracture propagations are likely.

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.>Choose conservative lines and watch for clues of instability.>

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 4

Wind Slabs

Recent storm snow is sensitive to human triggering and particularly deep and touchy in wind-loaded features.

Avoid exposure to terrain traps where the consequences of a small avalanche could be serious.>Be cautious as you transition into wind affected terrain.>

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 3

Cornices

Large and fragile cornices are will likely continue to fall of ridgecrests with sun exposure and temperature fluctuations. Not only are they a hazard in themselves, but also a heavy trigger for slabs on the slope below.

Extra caution needed around cornices with current conditions.>Cornices become weak with daytime heating. >

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 4

Valid until: Feb 24th, 2016 2:00PM