The bottom line: You can trigger avalanches in recent storm snow, especially above 4,000ft. Steer around steep roll-overs and convex terrain. Dig in the snow to check old snow surfaces for potential weak layers.
Snow and Avalanche Discussion
For Sunday, expect minimal wind and light snow accumulation. Concerns for avalanches will be primarily in the recent snow, but there are some old snow surfaces to watch. Depending location, aspect, and elevation, the recent snow is sitting on crusts, surface hoar, or facets. You can use snowpack tests to assess older weak layers 1-3 feet below the surface. If the sun comes out on Sunday afternoon, expect small loose avalanches on sunny slopes.
Regional Synopsis
January 16, 2019
Since Friday, January 11, we’ve enjoyed a spell of generally nice weather in the mountains. This allowed for some great views, enjoyable outings, and lots of snow observations. A more active weather pattern beginning Thursday, January 17th will bring this nice weather to a close.
During this time period, the snow surfaces around the area have changed dramatically. This forms the foundation for a few current trends we are seeing in the mountains.
New Snow Problems
Reports from around the area indicate a wide variety of snow surface conditions prior to new snow on January 17th. We’ve heard about breakable crust, very icy surfaces, sugar facets, surface hoar, and rime. What snow surface you encounter can depend on aspect, elevations, and general location.
As a series of winter storms impact the area, how will the new snow bond to the old snow surface? This can be tricky to predict. As the snow starts to pile up, make lots of shallow snow observations. Shovel tilt test, hand shears, and small slope test can all help you track how the new snow is bonding to the old snow at different aspects and elevations. Stop and take a look at where the snow is failing. Do you see large grains of snow? Do they look like feathers? Do they act like sugar? How far below the current snow surface are they?
Old Snow Problems
There are still lingering persistent weak layers in the eastern zones of the cascades. You are most likely to find weak older snow in areas further east from the Cascade crest where snowpacks are shallower, more variable, and generally weaker. In some locations, weak snow near the ground can still be found. These basal facets have hung around all season. The only way to gain information about these old persistent weak layers is to get out your shovel and dig. Because of the size of our forecast zones and the variability in the snowpack, it's important to make snow observations as you travel. We’ll keep watching these old layers, but let us know what you see while you are in the mountains.
Avalanche Problems
Storm Slabs
You can trigger storm slab avalanches on slopes over 35 degrees and generally above 4000ft. Over 8 inches of heavy snow fell overnight Friday into Saturday. The storm snow has classic strong over weak layering, set up for slab avalanches conditions. Use small test slopes and quick tests to check the bonding of the snow in the top 2 feet of the snowpack. Avoid steep roll-overs, convexities, and unsupported, rocky slopes. These trigger points are features where you can more easily trigger avalanches.
On Saturday, observers reported small natural avalanches about 8-10 inches deep in the storm snow below treeline in the Alpental Valley. If you travel to upper elevations, you may be able to trigger avalanches more easily in wind affected terrain. If the sun comes out on Sunday afternoon, expect small loose avalanches on sunny slopes.
