Avalanche forecast

Stevens Pass

Northwest Avalanche Center
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Avalanche danger

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Out of date — this forecast expired 6 years ago.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

Highlights

Heightened avalanche danger exists at upper elevations where you can trigger avalanches in recently drifted snow. At these same elevations, it may still be possible to trigger a very large and deadly avalanche on isolated slopes. The best way to deal with the uncertainty of triggering avalanches on deeply buried weak layers is to stick to slopes less than 35 degrees.

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Watch for triggering avalanches in recently drifted snow. Avoid leeward slopes where the snow looks thick and pillowed. Watch for wind features in the snow and areas of deeper snow adjacent to shallower areas. Feel for stiffer snow under your skis or feet as signs of drifting. Avalanches will be largest and most dangerous at the highest elevations. Sticking to windward, or non-loaded, slopes and terrain under than 35 degrees in slope angle.

    Westerly wind drifted cold snow onto wet, rain-soaked surfaces on Monday night as temperatures plummeted. This may have created a poor bond for newly formed wind slabs. Like the deep persistent slabs, it's a good idea to give the snow time to adjust and bond.  The photo to the right shows an impressive avalanche triggered in wind drifted snow on Tuesday.

    (12/22/2020) On Tuesday, avalanche workers intentionally triggered a fresh wind slab avalanche on an ENE aspect at 5,000ft near Stevens Pass. The crown was 200ft wide and 18-24" deep.

  • Deep Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Unlikely
    Size
    3

    Deep persistent slab avalanches could be very large and easily could bury or kill you. These dangerous avalanches can catch even the most experienced backcountry travelers. Triggering a deep persistent slab avalanche is unlikely but not impossible. With uncertainty about how easily you can trigger these avalanches, it's important to give them time to heal. You may get little warning before an avalanche occurs. 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.

    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. 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 weak grains have been rounding and gaining strength over the past week. The layer became active on December 14th and was involved in a widespread cycle of large, natural avalanches this past weekend. These avalanches occurred on a variety of aspects above 5,400ft. 

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

Avalanche Discussion

With sunny skies on Thursday, you may see a few small loose avalanches on steep southerly slopes. We're enjoying some quiet weather after what has been the most active and dangerous period of the season to date. This pause is a good time to recap recent avalanche activity.

On Tuesday, observers reported a cycle of avalanches near treeline in the 8" of snow that fell since Monday.  This came on the heels of a prolonged cycle of natural avalanches in the zone up to D3, (big enough to break a tree or bury a car) some with crowns over 4 feet deep. Some of these propagated widely, and most are suspected to have run on facets and surface hoar above the prominent December 9th crust. Smaller avalanches that ran 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 very large slab avalanches ran on Lichtenberg Mtn (both SW and SE) at 5600ft with crown depths 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. 

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