Avalanche Forecast

THURSDAY NIGHT: Snowfall slows down with 5 cm overnight, bringing storm totals into the 15 to 30 cm range, winds moderate to strong wind from the southwest and veering west, treeline temperatures steady around -3 C with freezing level falling to around 500 m. Around 1000 to 1500m is may remain at or above freezing overnight (temperature inversion).

FRIDAY: Mix of sun & clouds, light to moderate wind from the northwest, treeline temperatures around -2 C and freezing level again approaching 1000 m.

SATURDAY: Warming temperatures overnight with freezing level rising from 1500 m Friday at sunset to 2500 m Saturday afternoon. Above freezing temperatures to all but the highest peaks is possible. With an inversion developing valley floors will be colder under the valley fog. Mostly sunny, light wind from the northwest

SUNDAY: Warming pattern continues with zero or warmer temperatures between 1500 to 2500 m. Increasing clouds, light wind from the west or northwest. At lower elevations, under the valley fog, expect below freezing temperatures.

I take a long term view on the importance of recent avalanche activity -- events of the past week are relevant to the upcoming WARM weekend. This week we saw numerous very large (size 2.5-3.5) deep persistent slab avalanches occurring 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.

There were also numerous reports of smaller storm and wind slab avalanches reactive to human triggering. These smaller avalanches could step down to produce large avalanches in very rideable terrain..

The top 70 to 100 cm of snow of the snowpack is generally young and soft with a variety of little layers that may or may not be a problem. These include little surface hoar, thin crusts, and maybe even soft facets from early 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 be reactive with the upcoming warming.

The primary weak layer that remains a widespread concern across the Columbias 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.

• Dial back your terrain choices if you are seeing more than 20 cm of new snow.
• Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
• Storm slabs in motion may step down to deeper layers resulting in large avalanches.
• 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.