The Bottom Line: The snowpack is complicated in the East Central Cascades. As more snow accumulates and the wind creates fresh drifts avalanche danger will rise. This is a good time to step back, and focus on finding terrain to recreate in that isn't steep enough to avalanche.
Snow and Avalanche Discussion
Up to 7†of snow fell in the zone on the 17th with light winds. The Wenatchee Mountains east of Highway 97 were the winner. This likely preserved the old snow surface that consisted of a mix of facets, crusts, and old wind packed snow. On Thursday an observer reported collapses on a crust/facet sandwich layer down about 12" on an East aspect at 5800ft near Blewett Pass, a sign that a previous persistent weak layer is beginning to groan under its new heavy blanket.
Prior to the recent storm cycle, observes reported 'dramatic faceting' near and below treeline on shaded aspects. Another speaks of skiing on a ‘glass carpet’ of surface hoar between 4,000 and 5,500ft. Folks spoke of facet sluffs, a sure sign of very weak snow. We anticipate that the new snow won’t bond well with this old surface. The Salmon la Sac and Teanaway, and upper Icicle Creek stand to do better from this next storm rolling through into Friday. As the winds pick up and the snow accumulates, this will set the stage for our next round of avalanche activity. Avalanche danger will likely reach High by Saturday with a strong storm coming in Friday night.
Large, cup shaped surface hoar found in Icicle Creek on 1/14
Avalanche Problems
Wind Slabs
The winds will pick up on Friday after a mostly calm day. These, combined with a burst of new snow will form dense slabs, increasing the avalanche danger. Anticipate that these slabs won’t bond well with the old, weak snow surface that recently got buried. When you find more than 6” of new snow has drifted in or accumulated, it’s time to evaluate for slab characteristics. Look for shooting cracks within the new snow. Check how the new snow is bonding by using small, inconsequential test slopes and quick hand pits. Is there strong over weak? Is the new snow cohesive enough to crack? If so, it is time to avoid slopes steep enough to avalanche.
Aspects:
All aspects.
Elevations:
Alpine, Treeline.
Likelihood: Likely
Expected Size: 2 - 2
Persistent Slabs
Even if you are competent at evaluating and navigating through avalanche country, the complexities and intricacies of the snowpack are not to be taken lightly. The snowpack east of Highway 97 in the Wenatchee Mountains is substantially more shallow and weak than areas further west. Persistent slabs are a very real concern here, and in any area on the eastern edge of the range where less than 4 feet of snow is on the ground near treeline. Further west, the main layer of concern will be the new snow interface with the old snow surface.
Another layer of concern is associated with the January 3rd crust which can be found from 12” to 24” down. In the Wenatchee Mountains, this looks more like a pair of thin, friable, freezing rain crusts. Surface hoar and facets are sandwiched above, between, and below. In most places further west, the crust is supportable, but small facets can be found above this crust. Avalanches were observed on this layer as recently as January 12th starting on east aspects at 7000ft.
Finally, there is weak snow near the ground, particularly near the eastern edge of the forecast zone. If an avalanche failed on the ground, it would take the entire seasons snowpack with it, creating a very large and destructive slide. Be aware that this layer may begin to awaken with this new load, especially heading into the weekend.
