Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Sat
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
2 · Moderato
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In sintesi

The chance for very large avalanches is maintaining dangerous conditions. Ongoing warm temperatures, light precipitation, and isolated fresh drifts will add to the uncertainty. Continue to avoid traveling on or below large open slopes, especially at upper elevations.  

Problemi valanghivi

  • Deep Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    3–4

    The uncertainty 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 the prolonged warming 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

Avalanche Discussion

The warm temperatures continuing into Friday are especially concerning since we're only 4 days out from the last known deep slab avalanche. Other weather factors like light precip, rain at pass level, and blowing snow above treeline will complicate conditions. On Wednesday, a party was lucky to walk away uninjured from a cornice fall involvement on the Rooster Comb, adjacent to Stevens Pass Resort. Also on Wednesday, observers north of Stevens Pass reported hearing a loud booming noise that they suspected was cornice fall. This is good evidence that more cornices could fall and could trigger a larger avalanche. Given the bounty of uncertainty at play with avalanche conditions, forecasters remain concerned about the potential for 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 storm was on the heels of a whopping 6" of water equivalent and strong wind from February 20-23rd. 

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