Purcells

Storm conditions will quickly elevate the hazard on Saturday. We are uncertain how the snowpack will react to this new loading and are recommending very conservative terrain choices if you head out during the storm.

Fair - Timing, track, or intensity of incoming weather system is uncertain

A warm storm hits the region on Saturday. Models are currently showing 15-30mm of precipitation but freezing levels are forecast to stay around 2000m during the day so much of it will fall as rain. Freezing levels are forecast to drop down to below 1000m by Sunday morning so the rain may switch to snow at the end of the storm. Alpine winds are forecast to be strong during the storm and ease by Sunday morning. On Sunday, a mix of sun and cloud is expected with freezing levels around 1000-1500m and light alpine winds. There is currently uncertainty regarding Sunday night and Monday. A second storm pulse may affect the region but it also has the potential to track too far to the south and completely miss the region.

On Thursday, a cornice failure triggered a small wind slab on the slope below and a natural size 2 slab was reported from a steep rocky sun-exposed slope.  There have been some concerning avalanches in the neighboring Columbia regions over the last few days including natural slabs releasing to ground and very reactive wind slabs over facets being remotely triggered. Saturday's storm is expected to quickly build touchy new wind slabs where the precipitation falls as snow.  At lower elevations where the precipitation falls as rain, loose wet avalanches can be expected.  The major question and my biggest concern is whether deeply buried persistent weaknesses will wake-up with the new loading.  These persistent weak layers could have the potential to result in some very large persistent slab avalanches.  However, this is probably a low probability, high consequence type of problem.

A moist snow surface has been reported to around 2500m on solar aspects and 1800m on north aspects. Wind slabs have formed in the alpine and may be overlying the early-March crust/facet layer. The late-Jan crust/surface hoar layer can be found about a metre below the surface in deeper snowpack areas. The mid-January surface hoar can be found below that. These layers have gained significant strength and have been dormant for several weeks but have the potential to wake-up with the current warm temperatures.