Avalanche Forecast

Precipitation will begin on Friday evening, as a frontal system enters the region from the north. Moderate to heavy snowfall is forecast for Saturday, with a clearing trend forecast for early next week.

Friday Overnight: Cloudy with light precipitation, trace to 15 cm of new snow accumulation at higher elevations. Freezing level around 1500 m. Moderate to strong southwesterly winds. 

Saturday: A stormy day with moderate to heavy snowfall, 10-30 cm of accumulation. Freezing level around 1000 m. Moderate to strong southwesterly winds. 

Sunday: A mix of sun and cloud with light snowfall. Freezing level at valley bottom with alpine temperatures around -10 C. Light to moderate northwesterly winds.

Monday: Mainly clear. Alpine temperatures plummeting into the -20s. Light northeasterly winds. 

Natural and human-triggered storm slabs are likely on Saturday.

On Wednesday, we received numerous reports of reactive wind slab avalanches mostly up to size 1.5 and several larger ones up to 2.5 from alpine features. These wind slabs ran naturally and were easily triggered by the weight of a skier. Explosive control also initiated some larger persistent slabs up to size 2.5.

Last week, near-daily reports came in of human-triggered persistent slab avalanches on the January 30th weak layer, with the associated surface hoar layer taking both recreationists and professionals by surprise. The most reactivity on this layer has been seen between 1600-2200 m in open areas in the trees, in cut blocks, and on steep convexities. Reactivity has tapered, but we would continue to be cautious as the snowpack is tested with new load.

Continued snowfall throughout Saturday will add to 10-25 cm of recent storm snow above the old hard surface. This old surface is comprised of near-surface faceting, and in some areas surface hoar growth overlying a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline.

Several weak layers exist in the upper snowpack including buried crusts, facets, and a prominent weak layer of buried surface hoar. This surface hoar has been the dominating feature in the past few weeks and is most prominent in sheltered openings at and below treeline. It was buried in late January and exists 50 to 100 cm deep in the snowpack. Reactivity on this layer has begun to taper, but significant snowfall on Saturday could be enough to wake this layer up, initiating large and surprising avalanches. 

The facet/crust layer that formed in early December is now buried around 120 to 250 cm. The last reported avalanche was on January 31 from a large explosive, and before that on January 23. Although unlikely, the layer could be triggered from a large load like a cornice fall or a shallower slab avalanche could step down to this layer. 

• Storm snow and wind is forming touchy slabs. Use caution in lee areas in the alpine and treeline.
• Shooting cracks, whumphs and recent avalanches are strong indicators of an unstable snowpack.
• Be aware of the potential for large avalanches due to the presence of buried surface hoar.
• Surface hoar distribution is highly variable. Avoid generalizing your observations.