Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
2 · Moderato
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Non aggiornato — questo bollettino è scaduto 5 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Ongoing mild temperatures and strong sun will maintain a threat of wet avalanches on slopes steeper than 35 degrees. Time your travel to be off of and out from under sun-exposed slopes before the snow becomes wet and weak. Steer around wind features and drifts at upper elevations where you still may be able to trigger a large wind slab avalanche.

Problemi valanghivi

  • Loose Wet

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    Wet avalanches can develop quickly and catch you by surprise. They will first become active on the east aspects and later on the west aspects. Conditions may change dramatically through the day and as you change aspects and elevations. Plan ahead and be ready to move to more shaded aspects or slopes that are under 35 degrees. Take note of how much the surface snow has frozen or melted.  Anticipate when surfaces will become wet and weak. Move off of steep slopes before the snow is unsupportive and weak enough to entrain an avalanche.  

    Monday will be the second day in a slow and ongoing wet loose avalanche cycle. There's still enough dry snow available to produce avalanches especially at mid to upper elevations and on northeast and northwest aspects. Only the most northerly and shaded slopes are free from the effects of the strong April sun. 

    (4/11/2021) Natural wet avalanches ran in very steep, east-facing terrain. Stevens Pass zone

  • Wind Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1–2

    You may be able to trigger wind slab avalanches on leeward sides of ridges where slopes are steeper than 35 degrees. While these avalanches are becoming harder to trigger, they could still be big enough to kill you. Avoid thickly loaded leeward slopes and steer around unsupported and wind-sculpted features. Other indicators of wind slab conditions are textured snow surfaces and firmer or supportive dry snow.

    Wind slabs formed through the 10th with strong west through north winds. Slabs formed on a variety of surfaces and could be up to 2 feet deep. At Snoqualmie Pass, a skier was injured on April 10th after getting caught in a wind slab avalanche that ran on a layer of weak snow. While the same weak layer hasn't been observed in this zone, it's worth keeping an eye out for it. If you travel to upper elevations, look for hard-over-soft layering 1-2 feet below the snow surface on cold, shaded slopes. 

    (4/10/2021) A small wind slab avalanche triggered on an inconsequential test slope. This was on a leeward, 40 degree slope at ridgetop. Lanham creek, E, 5,450ft.

Avalanche Discussion

On Sunday, observers reported numerous wet loose avalanches with a few that were big enough to bury or kill a person. Some northerly aspects may have stayed dry, while other slopes quickly became moist. On Saturday, I went to Lanham creek and was able to easily trigger wind slab avalanches on small test slopes on the leeward sides of a ridge at 5,500ft. I also investigated northerly aspects, which held a mostly dry, winter-like snowpack. 

A storm starting on the 9th delivered 20-40cm of very cold snow with strong northwest winds. On Sunday, the sun came out and temperatures nudged above freezing but stayed relatively cool for this time of year. An earlier storm on the 7-8th brought 20-60cm of snow. This was also followed by a brief warm-up and wet avalanche cycle last week. Both storms brought the most snowfall to the mountains near and west of the pass.

Regioni coperte