Avalanche forecast

Stevens Pass

Northwest Avalanche Center
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Avalanche danger

Wed
Alpine
3 · Considerable
Treeline
3 · Considerable
Below
2 · Moderate
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Out of date — this forecast expired 6 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Dangerous avalanche conditions continue after a long period of heavy snow, rain, and strong wind near and above treeline.  Avoid being on, under, or near slopes 35 degrees and steeper at mid and upper elevations where you can trigger dangerous persistent slab avalanches. Small avalanches in surface snow are possible below treeline.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Likely
    Size
    2–3

    Persistent slab avalanches could be very large and could bury or kill you. These dangerous and surprising avalanches can catch even the most experienced backcountry travelers. With uncertainty about how easily you can trigger these avalanches, it's important to give them some time to heal. You may be able to trigger slides from long distances away. The best way to stay safe is to avoid where these avalanches exist. Keep your distance from slopes 35 degrees and steeper that are open enough and tall enough to produce large avalanches. Make sure you're not standing below or adjacent to steeper slopes. Use clues to stay out of avalanche paths, like trees stripped of uphill branches or openings in vegetation that continue up-slope. Watch for obvious signs of instability like recent avalanches, whumphing collapses, or cracks shooting through the snow.

    The most dangerous slopes will be at the highest elevations, where snow stayed mostly dry and where southwest to west wind drifted snow over the past few days. Avoid any areas that appear to be covered with thick drifts snow. You can find a thin weak layer of small facets (and in places surface hoar) above a crust buried about 3-4 feet below the surface. The layer became active on December 14th and was involved in a widespread cycle of large, natural avalanches on Dec 18th through the night of the 19th. What we know about these avalanches is that most occurred on northerly aspects above 5,400ft. There were a couple of reported slides that we suspect involved this layer on southerly aspects and as low as 5,000ft.

    (12/18/2020) Part of a remotely triggered persistent slab avalanche (D2) that was ~500ft wide and 15"-20" deep. Lanham creek, 5800ft, NE.

  • Storm Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    Watch for triggering avalanches in recent storm snow. Cold snow will fall with cooling temperatures on Monday night. Following travel advice for the Persistent Slab avalanches will keep you from triggering avalanches in the storm snow as well. At upper elevations, this new snow may be drifted and adding stress to the underlying weak layer. In addition, you may be able to trigger small avalanches on lower elevation slopes. At the lowest elevations, you may find heavy wet snow that has yet to freeze. 

Avalanche Discussion

The past week has been the most active and dangerous period of the season to date. Observers noted a prolonged cycle of natural avalanches in the zone up to D2.5 (big enough to injure, bury or kill a person) with some over 4 feet deep. Many of these had widely propagating crowns, and most suspected to have run on facets and surface hoar above the prominent December 9th crust. Some smaller avalanches reported on Sunday and Monday only involved recent storm interfaces and/or wet surface snow. On Monday, I caught a foggy glimpse of a couple of crowns in terrain adjacent to Stevens Pass Mountain Resort that ran on Friday and Saturday nights, including a size D2 on a northwest aspect around 5,400ft in Big Chief Bowl. On Sunday, observers reported a slab avalanche on Lichtenberg Mtn, SE, 5600ft with a crown depth estimated at 1-2 meters (up to 6 feet). On Saturday, observers reported a widespread cycle of slab avalanches mostly on northerly aspects above 5,000ft, including the northeast bowl of Arrowhead and much of the Rooster Comb, above Lake Susan Jane. On the 17th a party remotely triggered a large D2 avalanche on a northeast aspect at 5800ft above Lanham Lake with a crown about 500ft wide. On the 16th another party triggered a size D2 avalanche on a NE aspect at 5450 feet near the top of a peak northwest of Josephine Lake and Nasikelt peak. 

Regions covered