Expect avalanche danger to rise by Monday with precipitation favoring the west slope of the Cascades. Avalanche concerns will be most significant at upper elevations, while thin snow cover will continue to make travel difficult below treeline. Careful snowpack evaluation, cautious route finding, and conservative decision-making will be essential.
Avoid avalanche terrain if you observe warning signs such as shooting cracks, collapses, and recent avalanches.
Plan and prepare for changing conditions. The highest snow accumulations are expected near Mt. Baker, Mt. Rainier, and Snoqualmie Pass.
Snowpack and Avalanche Discussion
Heading into an active weather pattern, the common themes across the region are shallow snow cover and weak and variable snow surfaces. In the past week, observers reported widespread facets and surface hoar covering slopes in most regions. The potential for human triggered and natural avalanches will increase near and above treeline as the forecasted snow will not likely bond well to the old snow surface.
The recent stretch of cold clear weather has allowed the top few inches of the snowpack to become weak and faceted. Preserved surface hoar has been observed in several forecast zones. Andrew Kiefer photo.
Throughout the region, significant variation in snowpack structure exists at two scales:
1. Low and High Elevations
A winter snowpack has yet to develop below treeline in the Cascades and Olympics. New snow will be falling on bare ground or very shallow snow cover. Going up in elevation, the snowpack increases sharply, with an average of 2-3ft of snow on the ground above treeline. There have been no reports of recent avalanches at upper elevations.
2. West and East of the Cascade Crest
The snowpack structure varies as you move from the west side to the east side of the Cascade Crest. To the west, rain events and warm temperatures in late November have left a consolidated and strong mid and lower snowpack. Future instabilities will likely be the result of a poor bond at the new/old snow interface or within new snow. To the east, cooler temperatures and continued snowfall have preserved deeper buried layers of weak faceted (sugary) snow. These layers will have increasing potential to produce dangerous avalanches with an added load of new snow.