Bollettino valanghe

East Slopes Central

Northwest Avalanche Center
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Pericolo valanghe

Thu
Alta quota
3 · Marcato
Limite del bosco
3 · Marcato
Sotto il limite
3 · Marcato
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In sintesi

Expect increasingly dangerous conditions throughout the day with storm slabs becoming easier to trigger later. The new snow will also begin to stress persistent weak layers deeper in the snowpack, and you could trigger large and unsurvivable avalanches from steep open terrain features. Take a step back in terrain selection, and stick to lower angle and well-supported slopes while this winter storm plays out. 

Problemi valanghivi

  • Storm Slabs

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

    Storm slabs are expected to form during the day on Wednesday as the new snow stacks up. It'll be falling on a range of surfaces with an underlying theme of being weak and/or faceted. As such, the new snow isn't expected to bond well to the old surface. If you find signs of instability like shooting cracks, steer away from steep slopes. Small test slopes can work well, but with such variable old snow surfaces they may not be consistently reliable. The danger at upper elevations may be more pronounced by afternoon as strong winds readily create thicker slabs. If you observe that it's snowing hard, it's a good time to steer clear of steep slopes altogether. Besides slab avalanches, loose avalanches may run naturally during times of heavier snow.

    Any triggered storm slab could step down to more deeply buried weak layers, become very large, and propagate across terrain features. So increase your margins by sticking to lower angled slopes and creating a buffer zone between you and potential runout zones. 

    (1/7/2024)

    Example avalanche that failed on buried surface hoar in the Teanaway Drainage.

    Photo: Rob Pollard

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    2–3

    A problematic snowpack structure exists, and has been speaking to us with signs of instability like whumphing collapses as recently as Sunday. The new snow may begin to stress these deeper weak layers on Wednesday. Slab avalanches could be anywhere from 2-4 ft thick and have the potential to propagate widely across terrain features. Unfortunately, this structure is widespread throughout the zone and in many parts of the region. Additionally, a  layer of buried surface hoar from January 2nd sits an inch or two above a crust from December 30th and has been the culprit of several avalanches in the southern part of the zone. Persistent slabs take persistent patience. So, your best mitigation tool will be to stay off of large, steep and or unsupported slopes.

    (1/10/2024)

    Backcountry travelers near Lake Wenatchee remotely triggered this avalanche from a low angle adjacent slope. This avalanche ran on weak, facted snow over the Solstice Crust.

    Photo: Pat Riffie

Avalanche Discussion

Expect increasing danger on Wednesday. What you find first thing in the morning is likely to change a few hours later as snowfall stacks up.

Backcountry travelers have continued to report notable signs of instability, such as whumphing collapses and propagating test results. It's been a quiet few days, avalanche-wise, but that is likely to change. To make the situation more complicated, observers across the region have also reported pockets of surface hoar and near-surface facet growth from the recent cold, dry spell. The new snow may land on a variety of weak surfaces, even at low elevations. 

Last weeks storm dropped about 3ft of snow in much of the East Central, with about 1.5ft in the eastern Wenatchees. NWAC forecasters went to the lower slopes of Cashmere on Saturday and found small faceted grains over a crust above 3,000ft. This is the classic weak structure that can result in a persistent slab avalanche. Another NWAC forecaster visited the Salmon La Sac area last week. At 4600ft, she found around 70cm of new snow with a thin melt-freeze crust from a brief warmup midstorm buried 45cm down. This new melt-freeze crust showed potential for propagation in a snowpack test. Weak snow beneath the Solstice Crust also showed propagation in these test results. The bottom line is that its complicated out there, and its about to get even more tricky. So, it'll be best to take a step back in your terrain selection, and stick to lower angle and well-supported slopes as this next storm plays out.

If you get out, let us know what you see by submitting a public observation!

 

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