Bollettino valanghe

Stevens Pass

Northwest Avalanche Center
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Pericolo valanghe

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

In sintesi

Tuesday is a relatively calm day before the next winter storm arrives in the afternoon. Dangerous conditions persist with over 2ft of new snow at mid and upper elevations. Avalanches 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

    There's been a lot of new snow over the past two days. At lower elevations the storm snow is bonding well to old layers, but you could trigger a shallow soft slab that breaks within the soft new snow. How the storm snow is bonding to older layers becomes more variable the higher you go. Slabs could break within the new snow, at the old snow interface, or even deeper on a number of weak layers at higher elevations. If you find one of these areas, slides may fracture widely or be triggered from adjacent slopes. 

    You can look for signs of instability like recent avalanches, shooting cracks, and listen for whumphing collapses.  These are direct signs of instability, but there's no guarantee you'll get them as you travel or before triggering an avalanche. To hedge your bets, stick to lower-angled slopes and simple terrain, away from larger terrain features, especially at upper elevations. 

    Loose snow slides may also run fast and far on Tuesday. Look for fan shaped avalanches to clue you into these. 

     

    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. These may be most likely in the eastern portion of the zone, where the underlying structure is weaker. Control work triggered some slides down to this layer on shaded aspects on Tuesday, and skiers triggered a large and surprising avalanche on it in the adjacent East Central zone (Feb 22). Now that theres a heavy new slab of snow on top, conditions are primed for human triggering on some slopes. Slabs could be over 2.5ft deep, and fracture wide 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 hefty amount of new snow, 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

The storm totals keep ticking upwards. As of the time I wrote this there was about 20" of new snow at 4,800ft. Observers have been reporting significantly more snow with elevation. A wide natural avalanche was observed on a SE aspect at 5,600ft in Highlands Bowl, and control work at SPMR triggered a few avalanches that broke down to the early February Crust. Riding conditions continue to be excellent with the drop in temperatures, but unfortunately, stability remains in question. Tuesday will be another good day to give larger slopes some respect and consider sticking to lower angle and/or forested terrain. With another powerful storm knocking at our doorstep, very dangerous conditions are set to develop overnight into Wednesday. 

The intermittent dry spells we've had so far in February have created a number of potential weak layers, leading to a complex during this snowy week. These layers mainly exist above 5,000ft and on aspects but may be more prevalent on all but 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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