Avalanche Forecast

We have an inherently weak snowpack structure in the East Cascades. The weak layers themselves have been identified as buried surface hoar and/or buried near surface facets (from December 9) and appear to be blended into the form of basal facets and even depth hoar as one moves further east, or up in elevation. Basal facets have been observed in the Wenatchee Mountains, the Chiwaukum Range, and above 5500ft near Washington Pass. In short, it is a poor structure and one in which it will be hard to develop confidence in for some time.

Many areas within the zone saw a widespread cycle on December 11th. That said, there are some areas further east where the snowpack is thinner, received less precipitation during this time, and likely did not have a cycle at all. The details have yet to reveal themselves regarding avalanche activity from the storm on the 18th, due to low visibility and High avalanche danger. We do know that ski patrollers were successful at making explosive triggered slides within the new snow at Mission Ridge. One of these stepped down to basal facets near the ground, resulting in a 20" to 40" deep crown that propagated approximately 120 feet wide. This was on a Northeast aspect at 6400ft. An old professor of mine used to say “faceted grains are strong in compression, but weak in shear.” They can hold up to an enormous amount of weight, but when they do fail, wide propagations can be expected.

Why has the avalanche danger been so high for so long? Two reasons: A very active and wet weather pattern and widespread persistent weak layer.

For perspective, the approximate snow totals from 12/9-12/18 are:

• Mt Baker: 93”

• Washington Pass: 45”

• Stevens Pass: 66” mid-mountain

• Snoqualmie Pass: 59” mid-mountain

• Crystal Mountain 57” Green Valley

• Paradise: 70”

• Mt Hood Meadows: 37” mid-mountain

• Olympics: 20”

In many areas, a layer of buried surface hoar and/or weak sugary facets was buried on December 9th. This layer has been the cause in numerous natural, explosive, and skier triggered avalanches. As this layer gets deeper it gets harder to assess … in short, the scenario is tricky and getting more dangerous by the day.

Higher snow totals along the Hwy 542 corridor /Mt Baker area have driven several avalanche cycles during this period. Loading from recent storms has been more incremental to the east and south and we have not yet experienced a widespread cycle …

When will we reach the breaking point? It’s hard to say. What we do know is we have a deep weak layer, reports of very large explosives triggered slides at Mission Ridge and Crystal Mountain, and more storms on the way.

Be patient and continue to stick to lower angle slopes with nothing above you.  This is a good time to avoid areas where avalanches can start, run, and stop.

We’d like to thank all of you who have sent NWAC your observations. If you are out in the mountains, let us know what you see.