Bollettino valanghe

Snoqualmie Pass

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

Mon
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
Open full map
Non aggiornato — questo bollettino è scaduto 6 years ago. Stai vedendo condizioni passate, non il bollettino in corso.

In sintesi

Avalanches have been easy to trigger and should be another red-flag indicator for you to stick to conservative terrain on Sunday. Avoid slopes greater than 35 degrees if you see cracking in the snow or suspect wind-loading. The potential for weak layers deep in the snowpack to cause very large and destructive avalanches still exists.

Problemi valanghivi

  • Storm Slabs

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

    Storm Slabs were sensitive to human triggers on Saturday, with many recreationalists and professionals getting surprised by how easily the storm snow was failing. Slabs were failing easily at all elevation bands and should continue to do so on Sunday. The winds have been blowing from the east and have played a part in creating thicker and possibly more reactive slabs at all elevations, loading some unusual features. These slabs may break in surprising ways, propagate far distances, or even be triggered remotely. Use hand pits, uptrack tests, and test slopes as you travel to determine the reactivity and slab potetial of the new snow. Convex rollovers, steep open slopes, and rocky terrain near gullies and cliffs will be the most likely locations for you to trigger and avalanche. Many reports from Saturday indicated that treed slopes we often consider “safe” were showing signs of instability. Just because an area has trees doesn't mean that there aren't convexities, steep slopes, or a poor snowpack structure that can cause an avalanche. If you notice the snow surface cracking while you travel or blocks of snow failing easily in your tests, then avoid slopes over 35 degrees.

    (2/13/2021) This slab was remotely triggered by a skier on Saturday (2/13) at Snoqualmie Pass in an area generally considered as "safe". The debris ran across a popular travel route for skiers and snowshoers. [Photo: Andy Berner]

  • Deep Persistent Slabs

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

    Our persistent weak layers are getting buried deeper by the day. We have reported activity on these layers as recently as Thursday and they may still be active this weekend, especially with additional loading. You could travel all day or even several days in a row and not see any activity on these layers, giving you a false sense of security. Don’t get lulled into large start zones or big open slopes thinking that this problem has gone away. The weak snowpack structure is still in place, but we have some uncertainty around what it would take to trigger it at this point. We do know that any avalanche occurring on these buried weak layers would be very large and destructive. 

    (2/9/2021) Persistent slab avalanches that may have run naturally on an east aspect at around 4900ft in the Knox Creek drainage above Cle Elum Lake. These are suspected to have run on the mid-January crust later in the storm cycle of Feb 5-9th.

Avalanche Discussion

On Saturday, Alpental Pro Patrol reported sensitive slabs as deep as a foot triggered during control work. Multiple public observations reported sensitive slabs in the 6-10” range triggered by humans on both skis and snowmobiles. Many of these slides were triggered in the below treeline band or in the trees, which surprised a lot of people. As you might imagine, reports indicate that the new snow is not well bonded to the old snow surface. A subtle layer of weaker snow buried on 2/11 may be to blame for slides being so sensitive and breaking widely. The wind certainly was also a major player in creating slabs, possibly on aspects or elevations you may not be used to. Recent avalanches are a great red-flag indicator that the snowpack is unstable, and we saw a lot of them on Saturday.

The new snow instabilities and recent avalanches discussed above are enough on their own to drive Considerable danger, which is the level at which most avalanche accidents occur. Persistent weak layers lurking deeper in the snowpack should have you dialing back your terrain choices even more from what you would normally pursue at Considerable danger. These layers have been the cause of a week’s worth of near-misses and avalanche involvements, including a fatality earlier this week. It’s difficult to predict if or when this new snow will be enough to tip the scales and create very large avalanches on these layers again. Don’t leave it to chance, keep your terrain selection mellow and let us know what you’re seeing out there.

During the ongoing Covid-19 pandemic, continue to follow the latest guidance from local, state, and federal health officials. Avoid unnecessary risks that could impact first responders and stress medical resources.  Wear a mask when appropriate, practice social distancing, and consider recreating closer to home.

Regioni coperte