Avalanche Forecast

Issued: Feb 24th, 2016 8:35AM

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.

The snowpack is complex and quite variable right now. Buried weak layers remain reactive and conservative terrain selection remains critical. Extra caution is required during the heat of the day, especially on sun exposed slopes and around cornices.

Summary

Confidence

Moderate - Timing or intensity of solar radiation is uncertain

Weather Forecast

A ridge of high pressure keeps the region dry Thursday and Friday before a weak storm system arrives Saturday. Thursday is expected to be mainly sunny with light alpine winds from the southwest to west. Freezing levels are expected to drop below valley bottom overnight and reach 1700-2000m on Thursday afternoon. Friday is expected to be mainly sunny in the morning with increasing cloudiness during the afternoon. Alpine winds are expected to be light from the southwest but may increase during the afternoon and freezing levels are forecast to reach 2000-2500m. There is still a lot of uncertainty as to how warm it will get on Friday. A weak storm front is currently forecast to reach the region Friday overnight bringing 5-10cm of snowfall on Saturday.

Avalanche Summary

On Tuesday, a natural size 2 slab avalanche was reported from a gulley side wall feature on an east aspect at 2000m. This released down 80cm. Two natural size 1.5 storm slab avalanches were reported from northwest through northeast aspects at 2600m and released down 40cm. Numerous solar triggered loose avalanches up to size 2 were reported from steep south-facing slopes in the alpine. A natural size 3 cornice release was also reported from a northwest aspect at 2650m. Ski cutting produced several size 1 soft wind slabs from immediate leeward features. Explosives triggered a large cornice which released a size 2.5 persistent slab on a weak layer down 140cm on a northeast aspect. 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.

Snowpack Summary

A sun crust exists on south facing slopes at all elevations. Thin wind slabs are being reported in leeward features in the alpine and large cornices remain a concern, especially during the heat of the day. The surface hoar and/or crust layer from early February is now down 40-70cm and has been responsible for some large avalanches recently. This layer is expected to become most reactive during the heat of the day, especially on sun exposed slopes. The early January surface hoar/ facet layer is typically down 70-120cm. Triggering an avalanche on this layer has become unlikely but it still has isolated potential to produce very large avalanches with a heavy trigger. 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 40-70cm is susceptible to large triggers such as cornice falls or smaller avalanches stepping down. Wide fracture propagations are likely.

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

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

1 - 4

Wind Slabs

Lingering wind slabs in the alpine may still be reactive to human-triggers.

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

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 3

Cornices

Large and fragile cornices are will likely continue to fall of ridge crests 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.

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

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

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 4

Valid until: Feb 25th, 2016 2:00PM