Avalanche Forecast

TUESDAY NIGHT: Clear skies, light wind from the northwest, treeline temperatures around -12 C.

WEDNESDAY: Clear skies in the morning with increasing cloud in the afternoon, light wind from the southwest, treeline temperatures warming to -6 C.

THURSDAY: Moderate snowfall with 10-20 cm of new snow, strong wind from the southwest, treeline temperatures warming to -4 C with freezing level reaching 1000 m.

FRIDAY: Mix of sun and cloud, moderate wind from the northwest, treeline temperatures around -4 C.

A notable natural avalanche cycle occurred on Monday. Numerous very large (size 3) avalanches were reported in the Selkirks, including neighbouring Glacier National Park. These layers occurred at all aspects and elevations and involved both storm slab and deep persistent slabs.

The avalanche cycle was less dramatic in the Monashees, where there were primarily size 1 storm slab avalanches. However, there were two notable deep persistent slab avalanches in the Monashees that occurred on open treed slopes at 1750 and 1850 m.

Last week's warm storm produced a similar spike in very large deep persistent slab avalanches. We have ample evidence that this problem remains a very serious concern in the Columbias. Large avalanches will be most likely when this weak layer is stressed by heavy loads or dramatic warming.

20-30 cm of recent snow has likely been redistributed into leeward terrain at upper elevations. The upper snowpack contains a complex mix of crusts and small surface hoar layers. We are uncertain about where the most reactive layers may exist, but have noticed the following trends:

• A thin breakable rain crust is buried 30-50 cm deep and is found into the alpine in the Monashees and up to 1800 m in the Selkirks.
• A surface hoar layer is buried 40-80 cm deep and has been reactive in some sheltered terrain at treeline and below, particularly around Glacier National Park.
• A suspect layer of facets formed during cold weather at the end of December is 70-100 cm deep, but has not been reactive recently.

While none of these may be obvious widespread weaknesses, the combination and complexity require careful travel in avalanche terrain.

The one widespread weak layer in the Columbias is a more deeply buried crust/facet layer that formed in early December. It is typically down 80-140 cm, but as deep as 200 cm in wind loaded terrain. There has been regular avalanche activity on this layer at all elevations for over a month, and we expect to see continued sporadic very large avalanches.

• Be carefull around freshly wind loaded features.
• Carefully monitor the bond between the new snow and old surface.
• Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.
• Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
• Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.