Purcells

Strong solar inputs will destabilize the snowpack in the afternoon. Loose wet sluffing, cornice failures, and solar triggered slab avalanches are all possible and are most likely on steep sun-exposed slopes.

Fair - Due to the number of field observations

A ridge of high pressure should keep the region dry and mostly sunny until Friday afternoon. On Thursday, expect sunny conditions with light alpine winds and freezing levels reaching well over 2000m in the afternoon. On Friday, increasing cloudiness is expected during the day with alpine winds progressively increasing to moderate from the SW. Freezing levels are forecast to be around 1500m in the morning and around 2500m in the afternoon. On Friday afternoon or evening, a weak frontal system is forecast to reach the region. Models are currently showing 1-3mm of precipitation. By Saturday morning, the system should have passed and mostly sunny conditions are expected by Saturday afternoon. Freezing levels are expected to stay high for the weekend.

On Tuesday, skiers and explosives triggered storm slab avalanches size 1-2.  These were 30-60cm thick slabs on north through east aspects in the alpine.  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.  A skier also remotely triggered a storm slab avalanche from 30m away.  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.  Over the weekend, isolated natural avalanche activity up to size 2.5 was reported as well as skier triggered avalanches up to size 1.5. Solar triggered slab avalanches, cornice releases, and loose wet sluffing are all expected to have occurred on Wednesday. On Thursday, the same types of solar related activity are expected. If a supportive crust forms Wednesday night, stability will begin to improve. Human-triggering remains a major concern at higher elevations, especially north facing terrain where the storm slab is unaffected by the sun on Wednesday.

The sun on Wednesday is expected to have melted the snow surface at lower elevations and on sun-exposed slopes into the alpine. A new surface crust is expected form as temperatures drop overnight. In the north of the region, 20-60cm of recent snowfall overlies a weak layer that was buried on Friday. 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, strong SW winds have redistributed the recent storm snow forming thicker 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.