Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
Vedi sulla mappa

Pericolo valanghe

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

In sintesi

There's still a chance that you could trigger avalanches where you find hard over soft layering just below the recent snow.  A more likely scenario will be triggering loose avalanches in the surface snow. An abundance of cohesionless, dry snow and sunny skies, these avalancheches may be easier to trigger on Thursday.

Problemi valanghivi

  • Loose Dry

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

    Watch for natural loose avalanches especially on steep, sunny slopes as skies clear. Snow falling from trees or rocks could intitiate these slides. While we don't expect natural avalanches elsewhere, you can trigger them on a range of slopes, especially 40 degrees and steeper, or above unsupported features like rocks and cliffs. You can use small, inconsequetial test slopes to see how easily the snow slides.

    If you're in terrain that overlaps with Persistent Slab distribution, you need to manage the risk of that, more dangerous, problem. There, you won't be able to simply avoid surface instabilities.

    (12/9/2024)

    A triggered cornice fall on a leeward slope resulted in small loose dry sluffing.

    Photo: Katie Warren

  • Persistent Slabs

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

    Whumping collapses are a bullseye sign of unstable snow, and the best clue that you should stick to terrain under 35 degrees. Keep a large margin away from steeper slopes. The safest option for this problem is avoiding it altogether by staying on low-angle terrain or moving to other aspects.

    The problematic snowpack structure is where you find the recent snow at 4 Finger hardness or greater with an underlying weaker layer of sugar-like facets. West and southwesterly wind on the 1-2nd may have drifted stiffer slabs over the facets on  leeward slopes at middle and upper elevations. You'll need to probe or dig to feel for stiffer slabs as these will likely be under softer, more recent snow. Under the recent snow is a wide range of surfaces formed from the January Drought Layer. In addition to well-developed facets, you might also find pockets of huge surface hoar in deep valleys and sheltered terrain. Many slopes don't have much of a cohesive slab over these persistent weak layers. In these locations, you could trigger larger loose avalanches. 

    (1/19/2023)

    An example of a persistent slab in gladed terrain, like you might be able to trigger.

    Photo: Ryan Minton

Avalanche Discussion

For Thursday, temperatures will remain cold and sun will shine through clearing clouds. This could bring some changes (crusts or stiffening) to snow surfaces and the upper layers. While we don't have many observations of avalanches in the Stevens Zone, there have been many in other zones to the north and south. The main takeaway from the current snowpack is that it is very weak, and it's difficult to determine where you might trigger persistent slab avalanches. Avoid a "stepping out" mindset, until we have better confidence with these tricky conditions.Broken clouds and small amounts of sun on Tuesday may have allowed the recent snow to gain cohesion. From the 31st-2nd, about 2ft of snow fell on widely varying surfaces. In the days since, light snow has gradually accumulated to total another 9". The new snow fell at very cold temperatures and lacked cohesion. Backcountry travelers have reported more dry loose avalanches than slabs. Many observers reported reported widespread collapsing with a few reports of propagating test results. While many tests and observations show a lack of slab cohesion, we remain concerned with lingering instabilities on the January Drought Layer (JDL) on northerly aspects. 

An NWAC Forecaster was in the Henry Creek Area on Sunday to check on the state of our weak snowpack. Traveling through the low-angle clearcuts, they experienced numerous localized collapses and found two layers of concern in snow profiles. The deepest layer is buried 20-23in down and consists of 1-2mm faceted grains over the 1/10 crust. Above that, buried 15-20", is the surface of the January Drought Layer, which is 1cm buried surface hoar over another layer of 1-2mm faceted grains. I also observed a deep crown on a steep southern aspect at 5700ft, likely a wind slab that occured during strong winds on Saturday. 

You can help us build the forecast by submitting an observation HERE or via the Avy App. 

Regioni coperte