Avalanche Forecast

Across the northern interior ranges, heavy snow for the North Rockies will prevail Friday night. Up to 25 mm is forecast for the North Rockies with 10 mm for the Cariboo and North Columbia. Note that the North Columbia will receive the bulk of its precipitation on Saturday as the front slides south. Winds will be 30-40km/h with gusts to 50. 

Thursday Overnight: Snow 10 cm. Alpine temperatures -10 and freezing levels valley bottom. Strong westerly winds. 

Friday: Snow amounts 5-10 cm. Freezing level rising to 1800 m. Alpine temperature near -5 with strong westerly winds. 

Saturday: Snow 15-20 cm. Freezing level rising to 1500 m and alpine temperatures near -5. Strong West wind. 

Sunday: Snow 5-10 cm. Freezing level valley bottom and alpine temperature near -10. Moderate Southwest wind.  

Storm slabs will likely be reactive on Friday. Expect to see some reactive storm slabs and deeper wind slab on leeward slopes and terrain features. 

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 done 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. Reactivity has begun to taper but this buried weak layer should not be taken lightly as it may now present a low-probability, high-consequence problem. 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. 

Up to 20 cm of recent storm snow is expected to bond poorly to the old snow surface. This old surface is comprised of near-surface faceting, 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. It was buried in late January and exists 50 to 100 cm deep in the snowpack. The surface hoar is most prominent in sheltered openings at and below treeline.

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.