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Archived

Avalanche Forecast

Dec 22nd, 2018–Dec 23rd, 2018
Alpine
Below Threshold
The avalanche danger rating in the alpine will be below threshold
Treeline
Below Threshold
The avalanche danger rating at treeline will be below threshold
Below Treeline
Below Threshold
The avalanche danger rating below treeline will be below threshold
Alpine
Below Threshold
The avalanche danger rating in the alpine will be below threshold
Treeline
Below Threshold
The avalanche danger rating at treeline will be below threshold
Below Treeline
Below Threshold
The avalanche danger rating below treeline will be below threshold

Regions: Cascades - South East.

Very dangerous large avalanches are expected in many areas, particularly as you head into terrain close to the Cascade Crest. Old weak snow still exists and may fail, producing very large avalanches. Avoid all avalanche terrain.

Discussion

Snow and Avalanche Discussion

In areas receiving heavy snowfall and wind, expect a widespread and very dangerous cycle of large avalanches on Sunday.

You can still trigger very large and deadly avalanches. They could break much larger and wider than you expect. Persistent slabs have been much easier to trigger in the Eastern zones compared to neighboring areas to the west. Numerous large to very large avalanches have been reported from Washington Pass, Holden, and Mission Ridge. Some as recent as Thursday. 2-4 feet below the surface, you will find a layer of weak sugar-like snow that is the weak layer for these avalanches. To reduce your risk of being killed by a persistent slab avalanche, minimize your exposure to avalanche terrain:

Below treeline, the avalanche danger may be mitigated due to low snow conditions, but coverage and snow depth has increased over the few weeks.

Check the adjacent zones for more information that may pertain to this area.

Snowpack Discussion

Regional Synopsis: December 19, 2018

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

For perspective, the approximate snow totals from 12/9-12/19 are:

  • Mt Baker: 102”

  • Washington Pass: 55”

  • Stevens Pass: 76” mid-mountain

  • Snoqualmie Pass: 68” mid-mountain

  • Crystal Mountain 70” Green Valley

  • Paradise: 78”

  • Mt Hood Meadows: 44” mid-mountain

  • Olympics: 48”

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 of 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 snowfall 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 of the Mt. Baker area, so we have not yet experienced a widespread cycle in other areas.

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.