Bulletin d’avalanche

Stevens Pass

Northwest Avalanche Center
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Danger d’avalanche

Fri
Alpin
3 · Marqué
Limite forestière
3 · Marqué
Sous la limite
2 · Modéré
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Périmé — ce bulletin a expiré 5 years ago. Vous consultez des conditions passées, pas le bulletin en cours.

Points saillants

The chance for very large avalanches is maintaining dangerous conditions. Sun and warming temperatures will add to the uncertainty and could cause wet avalanches and cornice fall. Continue to avoid travel on or below large open slopes, especially at upper elevations.  

Problèmes avalancheux

  • Deep Persistent Slabs

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    3–4

    The unpredictability of these unsurvivable avalanches should keep you out of major avalanche paths. Avoid going into, or underneath open or sparsely treed terrain with large start zones above you. Continue to tread carefully and add a large margin of terrain between where you travel and where these avalanches could occur.

    A persistent weak layer of facets on or within a crust that was buried in mid-January has been the culprit for avalanches for over a month. Slopes 5000ft and above and on east/south/west aspects are of most concern. Avalanches have run up to size of D4, over 1500ft wide, and at least 10 feet deep as recently as March 1st. An added concern is the potential for warming and the sun to drop large cornices which could, in turn, trigger avalanches. Avoid slopes with overhead cornices. Make sure not to travel on overhung snow on leeward sides of ridges. 

    A deep persistent slab avalanche ran naturally at around 10:30pm on February 26th in a path known as West Camp on Rock Mountain above Highway 2 east of Stevens Pass. Southeast to Southwest aspects with the crown running from around 6200ft to 5400ft. Photo: WSDOT

  • Loose Wet

    • Alpin
    • Limite forestière
    • Sous la limite forestière
    Probabilité
    Possible
    Taille
    1–2

    Another day of warm temperatures and sun could be enough to see wet avalanches on steep slopes that have yet to slide in the past couple of days. If the snow is getting soft and wet, move to lower-angle and more shaded terrain.  These avalanches are generally easy to avoid and manage, but they can be dangerous around terrain traps.  With the uncertainty and dangerous conditions on Thursday, it's best to stay off of slopes prone to wet slides.

    Wednesday night will stay warm with freezing levels hovering at 5,000ft. During the day, cloud cover and wind will also be factors determining the likelihood of wet avalanches. Pay attention to how soft surfaces are and if the snow has melted enough to slide downhill. 

    (3/2/2021) Large rollerballs on a NE aspect at 4800ft in Henry Creek. Photo: Adam Butterfield

Avalanche Discussion

The warm temperatures Wednesday night into Thursday are especially concerning since we're less than 3 days out from the last known deep slab avalanche. Other factors like cloud cover and wind could determine the extent of melting or warming of the snowpack.  Given the bounty of uncertainty already at play with avalanche conditions, forecasters remain concerned about the potential for more very large avalanches. We're in a prolonged period of historically unstable conditions and dealing with a weak layer that has challenged even seasoned professionals. The deep slab problem continues to pose high consequences and demands conservative terrain and travel choices. 

Reports of impressive deep slab avalanches continue to trickle in involving the mid-January facet-crust layer. This includes very large natural avalanches on Benchmark and Fortune Mountains just north of Stevens Pass in the West Central Zone.  On Monday, WSDOT avalanche teams triggered an 8ft deep D3 avalanche on the southeast face of Rock Mountain east of Stevens Pass (the remaining hangfire in West Camp path), along with several D2 soft slab and wet loose avalanches. In the Chiwaukum Mountains, a natural D3.5 avalanche in upper-elevation north-facing terrain is suspected to have run on Sunday. At Snoqualmie Pass, very large natural avalanches ran on successive days into early this week, including an impressive D3.5 avalanche on Chair Peak. A massive avalanche (D4) ran naturally in the West Camp path on Rock Mountain last Friday night. Also last Friday, a partial burial occurred on the edge of the Stevens Pass Ski Area boundary, with the avalanche running on a storm interface.

These very large and destructive avalanches ran during a prolonged period of High to Extreme avalanche danger. A fast burst of snow, totaling about 2" of water equivalent accumulated by the night of February 26th with westerly wind driving direct-action avalanches into the 28th. This came on the heels of a whopping 6" of water equivalent and strong wind from February 20-23rd. 

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