Avalanche Forecast

The storms of the past week have been incrementally loading an inherently weak snowpack structure. The weak layers themselves have been identified as buried surface hoar and/or buried near surface facets, 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 in the East-North Zone.

Many areas within the zone saw a widespread cycle on December 11th. That said, there are some areas further east or where the snowpack is thinner that likely did not have a cycle at all.

For many areas this storm could be what pushes the stress vs. strength ratio of the slab vs. weak layer over the edge, resulting in large and widespread natural avalanching.

Updated Regional Synopsis 20181216

Dangerous and fickle avalanche conditions remain as active weather continues into the week. Thick slabs of new snow (2-5 feet) are perched above a weak layer of faceted crystals. Avalanches triggered on this layer could be very large and life threatening.

Reports continue to come in of very large natural and triggered avalanches in the northern and eastern zones. For perspective, several of these slides have been classified as D3, or large enough to destroy a house. You can find similar snowpack structure responsible for these avalanches in many other locations throughout the Cascades, including Stevens and Snoqualmie Passes.

Anyone accessing alpine areas should limit their exposure to areas where avalanches start, run and stop. In some places the weak snow will talk to you by whumpfing and cracking. In other places, the heavy blanket of new snow is thick enough that it can give a false sense of stability while it masks the dangerous layering below.

Approximate snow totals from 12/10 - 12/16:  

• Mt. Baker: 75”

• Washington Pass: 35”

• Stevens Pass: 42”

• Snoqualmie Pass: 36”

• Paradise: 51”

• Crystal Mt Base: 29”

• Mt. Hood Meadows: 21”

• Olympics: mix of rain and snow, no net gain

The change in the snowpack is pretty dramatic with elevation. Height of snow decreases rapidly below 4500’ at Baker and Washington Pass, 5500’ at Crystal/Rainier. The Passes have better low elevation coverage, but it's still pretty thin below 4000’. With additional warm storms in the forecast, this pattern is expected to continue for awhile. Mt. Hood and Hurricane Ridge have low snow coverage below 5000’.

If you're out in the mountains, please let us know what you see.

Be cautious and get home safe.