Bollettino valanghe

Swan Range

Flathead Avalanche Center
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Pericolo valanghe

Tue
Alta quota
2 · Moderato
Limite del bosco
2 · Moderato
Sotto il limite
1 · Debole
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In sintesi

It is possible to trigger a large avalanche that fails on a weak layer buried 1-3 feet below the surface. Recent northerly winds have drifted snow into thick, hard slabs in unusual locations. Both problems may not give you feedback until it is too late. Seek out terrain protected from the wind and avoid common trigger points. 

Problemi valanghivi

  • Persistent Slabs

    • Alta quota
    • Limite del bosco
    • Sotto il limite del bosco
    Probabilità
    Possible
    Dimensione
    1.5–2.5

    A weak facet/crust exists 1-3 feet below the surface. These layers have produced large natural avalanches in the past week. Although slabs are becoming more difficult for a human to trigger, the consequences may be severe.

    If you decide to flirt with steep terrain harboring these weak layers, your best chance of not triggering a large avalanche is to avoid common trigger points. These include convex rollovers and thin parts on the slab. Other ways to add margins for error are to choose slopes with long, smooth runouts and to only expose one person to steep terrain at a time. If you don’t want to dance with the dragon, stick to slopes with low slope angles. 

    (1/11/2024)

    The avalanche crown averaged 2.5 feet thick and failed naturally or was remotely triggered. This is an out-of-bounds avalanche in a popular side-country location just east of the WMR ski area.

    Photo: Mark Dundas

  • Wind Slabs

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

    Recent north and east winds have drifted snow into hard slabs at all elevations. Cold temperatures are slowing the strengthening process of these old slabs of drifted snow. Look for and steer around dune-shaped drifts and feel for hard, hollow-like snow beneath your feet or machine. Hard slabs are difficult to manage and may not fail until you are way out on the slope. Your best tool for managing hard slabs is by avoiding terrain where they exist.

    (1/12/2024) Crown in the upper reaches of Shed 9 on Snowslip Mtn Photo: Adam Clark

Avalanche Discussion

Although the danger rating is Moderate, the avalanche conditions remain tricky. The likelihood of triggering a large slab avalanche is becoming less, yet still possible. Cold arctic air remains in place and can turn a simple mishap into a life-threatening situation.

The largest uncertainty in today’s avalanche problem rests with the Persistent Slab problem. Arctic air has kept many users out of the backcountry, reducing the number of observations. Due to the higher-than-usual uncertainty, the safest bet is to treat all slopes above 5000 feet as potential suspects for having these weak layers. The picture is not totally clear yet with this problem, but here is what we know:

  •  Reported avalanche activity failing on persistent weak layers has occurred on east-facing aspects between 5000-7000 feet (see visual). Additionally, north of the border, a rider remotely triggered two large avalanches failing on a similar weak layer. These occurred on January 10th (observation).
  • Before the storm, facet/crusts and weak surface snow were documented on most aspects above 5000 feet. The facet/crust appeared weakest and most noticeable at middle elevations (photo facet/crust before the storm).
  • The weak layer is buried 1-3+ feet down from the surface. It will be buried deeper where winds have drifted more snow. You will be able to feel it with your probe or pole in areas where it does exist.
  • The snowpack is significantly thinner the closer you are to the continental divide. In that terrain, look for large facets near the ground (observation, avalanche observation).

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