North Columbia

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.

FRIDAY NIGHT: Cloudy with isolated flurries; 0-3 cm. / Moderate, northwest ridgetop wind / alpine low temperature -13 / Freezing level valley bottom.

SATURDAY: Flurries; 5-10 cm. / Moderate, west ridgetop wind / alpine high temperature -10 / Freezing level valley bottom.

SUNDAY: Mix of sun and cloud / Moderate, northwest ridgetop wind / alpine high temperature -13 / Freezing level valley bottom.

MONDAY: Sunny / Light, west ridgetop wind / alpine high temperature -15 / Freezing level valley bottom.

A skier triggered size 2 persistent slab avalanche that failed on surface hoar around 60 cm. down was reported near the Gorge area on Thursday.

There have been many recently reported avalanches on a widespread persistent weak layer surface hoar throughout this region. Here is one excellent example from the Gorge area and another from Corbin Pass.

Persistent slabs are sitting on a very 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.

60-100 cm. of recent snow is sitting on a very reactive 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.

A less reactive layer of surface hoar or facets buried in early January can be found down 80-130 cm.

The mid/lower snowpack is generally well settled and strong. 

• Be aware of the potential for large avalanches due to the presence of buried surface hoar.
• Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
• Avoid open slopes and convex rolls at and below treeline where buried surface hoar may be preserved.
• Be careful as you transition into wind affected terrain.