The Bottom Line: New snow over the old surface will be the main concern. Light snow accumulations probably won't be enough to create much avalanche danger on Thursday, but avalanche danger will increase overnight and into Friday. Icy crusts may create challenging travel conditions.
Snow and Avalanche Discussion
The current snow surface is a mix of facets, crusts, and wind packed snow. On shaded aspects, weak snow on the surface is widespread in the area. We don’t have a great handle on the upper elevation extent of the weak snow in this area, but one observer reports skiing on a ‘glass carpet’ of surface hoar between 4,000 and 5,500ft. Another notes ‘dramatic faceting’ near and below treeline on shaded aspects. Folks speak of facet sluffs, a sure sign of very weak snow. As the snow accumulates into Friday, this will set the stage for our next round of avalanche activity.
New snow accumulations will be light on Thursday. However, we anticipate that whatever new snow does accumulate won’t bond well with the old surface. Continue to use standard practices and protocols for winter travel in the mountains. This includes minimizing exposure to the avalanche hazard and carrying standard rescue gear. Avalanches are unlikely, but not impossible. If you find more than 6†of new snow has drifted in or accumulated, it’s time to consider slab avalanches again. It's important to keep in mind the consequences of an avalanche in extreme terrain or that of a non-avalanche related injury or gear malfunction in a remote setting.
Large cupped surface hoar found growing over a thin, decomposing rain crust in Icicle Creek near Leavenworth on 1/14.
Avalanche Problems
Persistent Slabs
Evaluate the snowpack carefully as a weak layers may still be found at mid and upper elevations. It would likely take a very large load to initiate an avalanche on these buried weak layers. Uncertainty is higher outside of the Washington Pass corridor regarding these layers and in any place where the snowpack is less than 4 feet deep near treeline.
There are two persistent weak layers of concern:
1. A layer of buried surface hoar may be found 1-3 ft below the snow surface. This is mainly a concern above 6000ft. Be suspicious of this layer the higher you go. Documented avalanches occurred on north through southeast aspects. Snowpack tests have continued to reveal sudden results in some areas on this layer.
2. A layer of weak sugary facets can be found near the ground, particularly near the eastern edge of the forecast zone. If an avalanche failed on this layer, it could be more than 4 feet deep. Use caution if you are traveling in areas where the snowpack is thinner.
