Avalanche Forecast

Issued: Feb 25th, 2016 8:09AM

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

Avalanche Canada rbuhler, Avalanche Canada

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 mix of sun and cloud is expected for Friday with moderate southwest winds in the alpine. A temperature inversion is expected with a layer of above-freezing air sitting around 2000m elevation and colder temperatures in the valleys. A weak storm pulse is expected to bring around 5cm to the region on Saturday morning. Alpine winds are expected to be moderate from the southwest on Saturday with freezing levels around 1800m. Mostly dry conditions are expected Saturday afternoon through Sunday morning before a second weak storm pulse arrives Sunday afternoon.

Avalanche Summary

On Wednesday, a natural size 3.5 slab avalanche was reported from an east aspect at 2700m which released down 100cm and was 250m wide.  Three natural cornice releases size 1.5-2 were reported in the high alpine.  Numerous size 1.5-2 natural loose avalanches were reported from south aspects in the alpine.  Explosives triggered three slab avalanches on northern aspects which were 10-30cm thick. On Tuesday, a natural size 2 slab avalanche was reported from a gulley side wall feature on an east aspect at 2000m which released down 80cm. Also reported on Tuesday were skier triggered wind slabs, natural storm slabs, loose dry sluffing from steep sunny slopes, and large cornice releases. There is a lot of uncertainty for how reactive the snowpack will continue be on Friday with the continued warm temperatures and sun.  I expect that the buried weak layer from early February will continue to produce large destructive avalanches with heavy triggers such as cornice falls or smaller avalanches stepping down, but it may also still be possible to directly trigger this layer in some areas.  Sluffing can be expected from steep sun exposed slopes and cornices will become weak with warming and sun.

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

An icon showing Persistent Slabs
A weak layer of surface hoar and/or a crust down 40-70cm remains susceptible to large triggers such as cornice falls or smaller avalanches stepping down. It may be still be possible to directly trigger this layer during the heat of the day.
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

Expected Size

2 - 5

Wind Slabs

An icon showing Wind Slabs
Lingering wind slabs in the alpine may still be reactive to human-triggers.
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: North, North East, East, South East.

Elevations: Alpine.

Likelihood

Possible

Expected Size

1 - 2

Cornices

An icon showing 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.
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 26th, 2016 2:00PM