Strong solar inputs will destabilize the snowpack in the afternoon. Loose wet sluffing, cornice failures, and solar triggered slab avalanches are all possible. A tricky weak layer is expected to be most reactive on high elevation north aspect slopes.
Summary
Confidence
Fair - Due to the number of field observations
Weather Forecast
Warm, sunny conditions dominate the weather for the forecast period. On Friday, a mix of sun and cloud is expected with moderate winds from the SW to NW and freezing levels reaching around 2500m or higher. A weak frontal system is forecast to bring increased cloud cover for Friday evening and light scattered flurries are possible in the north of the region. On Saturday, mostly sunny conditions are expected with light NW winds in the alpine. Freezing levels are expected to be around 1500m in the morning and around 2300m in the afternoon. A mix of sun and cloud is expected for Sunday with light alpine winds and similar freezing levels.
Avalanche Summary
On Wednesday, natural solar triggered avalanches to size 2 were reported. Explosives triggered several slab avalanches and a skier triggered a size 1.5 on a convex roll feature. A remotely triggered avalanche was also reported and was triggered from 25m away. On Tuesday, skiers and explosives triggered storm slab avalanches size 1-2 which were 30-60cm thick. Explosives were also used to trigger a cornice release which subsequently triggered a size 3 slab avalanche that may have stepped down to a deeper layer in the snowpack. Several remotely triggered avalanches have been reported in the last few days from up 100m away as well as whumphing and wide propagations. This suggests that the weak layer below the storm slab has been very reactive in some areas. Solar triggered slab avalanches, cornice releases, and loose wet sluffing are all expected to have occurred on Thursday with the big warm-up. On Friday, the same types of solar related activity are expected. If a supportive crust forms Thursday night, stability will begin to improve. Human-triggering remains a major concern at higher elevations, especially north facing terrain where the storm slab has been unaffected by the sun.
Snowpack Summary
Warm temperatures and strong solar are rapidly changing the upper snowpack. A moist snow surface is expected to exist to well over 2000m elevation on north aspects and to ridgetop on solar aspects. Overnight refreeze on Thursday night is expected to form a widespread surface crust which is expected to be supportive and capping at lower elevations. Down 20-60cm is a weak layer that was buried last Friday and has been very reactive recently. This weak layer typically consists of surface hoar and facets overlying a melt-freeze crust that exists everywhere except high elevation north-facing terrain. In exposed alpine terrain, recent strong SW winds had formed wind slabs in leeward features. Large cornices exist in the alpine and may become weak with daytime warming. There are three dormant persistent weak layers that we are continuing to track. The late-March crust is down 50-70cm and was reactive last week during the warm period. The mid-March and mid-February layers are typically down between 70 and 100cm and have been dormant for several weeks. These layers have the potential to wake up with sustained warming, a significant rain event, and/or a big cornice fall.
rbuhler,
Avalanche Canada
