Continued discipline and careful route finding will be required on Saturday to avoid triggering large avalanches on a buried persistent weak layer of surface hoar. This layer has been especially reactive at treeline elevations.
Southwest switching to northwesterly winds may form reactive wind slabs on a variety of aspects at treeline and above.
40-60 cm of recent snow has formed reactive slabs sitting on a persistent weak layer of surface hoar. These slabs may be especially reactive in wind affected terrain.
FRIDAY NIGHT: Cloudy / Strong, northwest ridgetop wind / alpine low temperature -16 / Freezing level valley bottom.
SATURDAY: Cloudy with flurries; 3-10 cm. / Moderate, west ridgetop wind / alpine high temperature -7 / Freezing level valley bottom.
SUNDAY: Mix of sun and cloud / Moderate, northwest ridgetop wind / alpine high temperature -12 / Freezing level valley bottom.
MONDAY: Sunny / Light, northwest ridgetop wind / alpine high temperature -13 / Freezing level valley bottom.
There was a recent report of skier remotely triggering a size 2.5 persistent slab from a ridgetop at treeline near Quartz Creek on Wednesday. This avalanche failed on the very weak layer of surface below the recent storm snow. It was reported that light wind effect had stiffened the recent storm snow just enough to be highly reactive to skier triggering. Min report HERE.
Touchy storm slabs are sitting on a weak layer of surface hoar which is likely to be reactive to human triggers. Avalanches may be larger than expected due to the presence of this weak layer.
Southwest switching to northwesterly winds may form reactive wind slabs on a variety of aspects at treeline and above.
40-60 cm. of recent snow is sitting on a very weak layer of surface hoar which has potential to surprise backcountry users by how easily it may be triggered and how wide the persistent slabs propagate across slopes. Recent avalanches on this layer have primarily been reported at treeline and below.
60-100 cm. down is an older surface hoar and/or a thin melt crust from mid January. This layer was more prominent in the north Purcells in sheltered, open slopes at treeline.
Deep persistent weak layers can still be found in the lower snowpack. These weak layers are most likely to be triggered from rocky areas with a shallow or thin to thick snowpack.
