Avalanche Forecast

SUNDAY NIGHT: Broken skies, cooling overnight. Decreasing northwest wind, temperatures dropping to -8 C, freezing level to valley bottom.

MONDAY: Broken skies, clearing in the afternoon. Light northwest wind, high temperatures dropping to -5 C, and freezing level dropping to valley bottom.

TUESDAY: Sunny. Light southwest wind. High temperature -6 C. Freezing level at valley bottom.

WEDNESDAY: Sunny with increasing cloud. Increasing southwest wind. High temperature -8 C.

On Saturday, explosives near the Trans Canada triggered very large avalanches (size 2.5-3.5) failing on the early December facet/crust layer. This included a historical size 4.5 avalanche which started at ridgeline, created new trim lines, and destroyed mature timber. Avalanche reports also included small (size 1-2) wind slab avalanches reactive to skiers and failing naturally; and solar radiation-triggered wet-loose avalanches to size 2 on southerly aspects.

Between Thursday and Friday, large (size 1.5-2.5) storm and wind slab avalanches failed naturally, these averaged 30-60 cm deep, and in some cases a weak layer of surface hoar was reported at the interface. In the same timeframe, another round of very large (size 2.5-4) deep persistent avalanches failed naturally, with rapid loading and warming temperatures being the likely trigger. An impressive report documents a size 4 avalanche in Rogers Pass here.

The past week numerous very large (size 2.5-3.5) deep persistent slab avalanches occurred in both the Selkirks and Monashees. These avalanches failed on the early December facet/crust layer, typically 100-150 cm deep. One notable pattern is that many of these avalanches released at relatively low elevations (1700 to 2000 m) in open clearings, burns, and slide paths. In many cases, they were triggered by smaller avalanches starting at higher elevations. This layer is likely to plague our snowpack for the remainder of the season and will be a low probability but extremely high consequence result if triggered.

A variety of snow surfaces can be found: crusts at lower elevations and solar slopes into the alpine, wind press and wind slabs in open and exposed terrain, and dense powder in sheltered areas. Surface hoar growth has also been reported.

The most recent snowfall covered a layer of surface hoar now down 20-30 cm, this interface was responsible in the most recent natural storm slab avalanches reported Jan 20-21. The top 50-100 cm of snow of the snowpack has variety of little layers that may or may not be a problem. These layers include surface hoar and crusts from January snowfalls and facets buried at the start of January. While none of these upper layers are necessarily going to remain a long-lasting problem, there is a fair bit of uncertainty about their spatial distribution and whether they will remain reactive with the warm temperatures.

The primary weak layer that remains a widespread concern across the Columbia Mountains is a deeply buried crust/facet layer that formed in early December. It is typically down 100-150 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 avalanche activity continue on this layer.

• Pay attention to the wind, once it starts to blow fresh sensitive wind slabs are likely to form.
• Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
• The trees are not the safe-haven they normally are. Terrain at and below treeline is capable of producing large destructive avalanches.
• Uncertainty is best managed through conservative terrain choices at this time.