Warm and windy storm conditions are expected to drive the avalanche hazard to HIGH on Saturday morning. Storm slabs overlie a touchy weak layer which may increase the potential for wide propagations and remote triggers.
Summary
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
Warm storm conditions are expected for Friday overnight and Saturday morning with 10-15mm of precipitation forecast and freezing levels reaching around 2300m. Alpine winds are expected to be strong from the southwest. A dry break is expected for Saturday afternoon before the second storm front arrives Saturday night. Another 15-20mm of precipitation is expected by midday Sunday. Freezing levels are expected to stay above 2000m during this second storm and alpine winds should stay strong from southwest. Monday is currently forecast to be mainly dry with cooler temperatures.
Avalanche Summary
On Thursday, a size 1.5 storm slab was ski cut on a northwest aspects at 2050m. This slab failed on the late-February surface hoar layer down 25-30cm. Numerous small ski cut avalanche were also reported to be failing on this layer through the region. Loose sluffing was also reported from steep sun exposed slopes. On Wednesday there was a report of a size 2.5 avalanche that was remotely triggered by a group on a ridge. This avalanche occurred in the northern part of the region on a NE aspect. In addition, there were reports of numerous size 1.5-2 natural storm slab avalanches and several size 2 explosive triggered storm slabs. These were on a variety of aspects between 1900 and 2100 m elevation. The slabs were releasing on the late-February crust/surface hoar layer down 30 cm. Natural slab avalanche activity is expected during the storm on Saturday due to the combination of new snow, strong winds, and warm temperatures, which is expected to overload the weak surface hoar layer from later February.
Snowpack Summary
30-40cm of recent storm snow overlies a layer of well-developed surface hoar (up to size 20mm) which is very reactive to human triggers. This layer is widespread above 1700m except on south aspects where the interface was cooked by the sun and now exists as a buried sun crust. Significant wind transport has been noted so expect to find deeper, more destructive slabs in exposed lee terrain. 80-100cm below the surface you will likely find the mid-February crust/facet/surface hoar layer. Although this layer has become less likely to trigger, avalanches failing at this interface could be large and destructive.
rbuhler,
Avalanche Canada
