Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

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

Dangerous conditions exist with 2ft of new snow at mid and upper elevations. Slopes are now primed for human triggered slab avalanches, these could be up to 3ft deep if they break on more deeply buried layers of facets and crusts. With potential to trigger large and wide slabs, stick to lower angle or lower elevation slopes. 

Problemi valanghivi

  • Storm Slabs

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

    The new snow is stacking up quickly. Storm slabs should be most reactive in the morning, and instability is expected to linger through the day, especially at middle and upper elevations. Slabs could break within the new snow, at the old snow interface, or even deeper on a number of weaker layers at higher elevations. The new snow recently buried a layer of facets and surface hoar on sheltered, shaded slopes above 5,000ft. If you find one of these areas, slides may fracture widely or be triggered from adjacent slopes. Loose snow slides may run fast and far on Monday. Look for fan shaped avalanches to clue you into these.

    You can look for signs of instability like shooting cracks, and listen for whumphing collapses. Although with over 2ft of new snow and variable underlying layers, you may not receive direct signs of instability. Stick to lower angled and simple terrain, away from larger terrain features especially at upper elevations. 

     

    Example storm slab in terrain below treeline.

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Likely
    Dimensione
    2–2.5

    At and above 6,000ft, slides could run on more deeply buried weak layers including weak snow and a crust from early February. This weak structure has recently produced large and surprising avalanches in the adjacent East Central zone. Now that theres a heavy new slab of snow on top, conditions are prime for human triggering in this area. Slabs could be over 2.5ft deep, and break widely across terrain features. Whumphing collapses are good indicators that you could trigger a large persistent slab, but if you don't receive these signs it doesn't mean that you can't trigger one. 

    With a complex snowpack and dangerous conditions, keep it simple with your terrain choices. Use well supported and lower angle slopes, and stay well away from larger open faces.

    (2/22/2024)

    A skier triggered avalanche (D2) on facets above the early February crust. The crown was 100' wide x 4"-1.5' deep and it was triggered from below on a 30-degree terrain. It ran to either side of the low-angle slope. 6,200ft in East Central zone.

Avalanche Discussion

Sunday was a very stormy day. Temperatures were warm with snow line right around pass level most of the day. Observers found about a foot of new snow at Skyline Lake at 11am, 2ft at 5,000ft by 2pm, and it continued to snow. You're likely to find a couple feet of new snow or more at 5,000ft by Monday. Riding conditions should be quite good with the drop in temperatures, though unfortunately stability is in question. It'll be a good day to give larger slopes some serious respect. Monday might be a nice day to stick to forested terrain. 

The intermittent dry spells we've had so far in February have created a number of potential weak layers, leading to a complex set up going into a snowy week. We expect these will begin to get stressed and break at some point, the question is when. These layers mainly exist above 5,000ft and on aspects besides due south. Check out the obs from forecasters on Jim Hill on the 19th and see the profile and images of the weak grains in the gallery below. In the East Central zone, backcountry travelers have triggered a number of avalanches just above the early February Crust. The most recent was on the 22nd and was up to 1.5ft deep on a W aspect at 6,200ft in the Teanaway.

If you get out, you can submit an observation here.

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