Avalanche forecast

Selkirk Mountains

Idaho Panhandle Avalanche Center
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Avalanche danger

Sun
Alpine
2 · Moderate
Treeline
1 · Low
Below
1 · Low
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Highlights

Upper-elevation slopes with fresh wind-drifted slabs increase your chance to trigger an avalanche today. Steer clear of slopes with fresh cornice growth above or those that look smooth, rounded, or pillowy. Cracking in the snow surface is a clue you've traveled onto a heavily drifted area. Safer travel and riding options are found on sheltered slopes lower in elevation free from active wind-drifting.

**On January 6, a very-large (D3) glide avalanche released in St Regis Basin in the Bitterroot Mountains. Additionally, the forecast staff has observed several other glide cracks in the Silver Valley and areas north that warrant attention. Avoid traveling on or below slopes where a glide crack has opened up. These types of avalanches are difficult to forecast when they will release.**

Avalanche problems

  • Wind Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–2

    Two to four inches of new snow fell across the Idaho Panhandle and Western Montana on Friday and overnight. New snow was accompanied by moderate to strong west-southwest winds. Despite snowfall tapering Friday afternoon, moderate winds have continued and will keep transporting snow onto leeward-facing slopes. Fresh slabs formed on a variety of old snow surafces like crust, wind-stiffened snow, or soft more cohesionless snow. Depending on what's directly below, you may experience varying sensitivity in freshly drifted slabs. At lower elevations, IPAC field staff on Friday reports lighter winds and less slab formation.

    Keep an eye out for typical signs of wind transport, such as scoured ridgelines, fresh cornice growth, and lens-shaped pillowy areas that are firmer. Deeper, more concerning drifts will be found below ridgelines, in cross-loaded gullies, and possibly further down on slopes that usual from prolonged stronger winds. Monitor how snow depths and surface stiffness changes as you climb higher or change aspects. Hand pits, test slopes, and other informal methods to evaluate the uppermost layers can provide insight to bonding at the new-old interface. New snow hazards often find equilibrium quicker than persistent grains, so stick to lower-angle slopes for another day and allow these fresh slabs to mellow out before stepping out into bigger, more challenging terrain.

    This is a small crack in the wind slab. IPAC Field staff experienced this yesterday as they walked along a newly wind-loaded slope near Jeru mountain in the Selkirks.

    Photo: Jeff Thompson

Avalanche Discussion

The primary snowpack hazard is wind loading from Friday's storm. Although the wind event was relatively short-lived, winds were sustained long enough to transport both new and existing snow onto leeward slopes forming fresh slabs. Stong gusts can erode thin crust on southerly-facing slopes helping enhance snow transport. As prominent wind direction transitions from southwest to west to northwest, expect slab formation to extend their reach and possibly exist lower on the slope than you usually find them. Broad openings are more likely to develop larger hazards more quickly than treed areas near the timberline, where similar slabs may be more isolated. You can use small, test slopes to assess the sensitivity of fresh drifts before venturing into steeper, larger slopes, or you can stick to wind-sheltered areas and lower-elevation terrain.

The lack of recent natural avalanches and rider-triggered slides failing in one of the deeply buried faceted rain crusts, we've decided to remove the Persistent Slab avalanche problem. Snowpack tests have mostly stopped producing failures in these deeper layers, but isolated locations still produce propagating results - albeit with hard force or many loading steps. The grains immediately above and below both the December 7 and 18 rain crust are showing evidence of rounding and those interfaces are becoming thinner and harder. In summary, the weight of the overlying slab is helping squash these weaker interfaces making them very stubborn to unreactive.

During periods of lower-likelihood, higher-consequence scenarios, solid terrain management is crucial to offset uncertainty. Given the limited recent field observations above 7,000 feet, be aware that traveling to higher elevations could expose you to terrain where faceted grains may still be preserved. However, the slab above is likely to be thicker and stiffer. Avoid steep, rocky areas with abundant trigger spots, and choose slopes free of vegetated runouts or terrain traps to minimize your risk around the "what-if" scenario. Also, be mindful of other groups in the area, and only expose one person to a slope at a time.

A recent large glide avalanche that occurred on the night of January 6 in the St. Regis Basin, visible from Lookout Pass Ski Area. As well, several glide cracks in the Silver Valley and areas north are worth noting. Glide avalanches can involve wet, moist, or nearly dry snow and can release under both warm and cold conditions. These avalanches occur on very specific slopes with relatively smooth ground surfaces, such as slick bedrock or grassy slopes. Glide avalanches are often preceded by full-depth cracks visible across the slope. However, the time between the appearance of a crack and an avalanche can vary from seconds to months. Glide avalanches are unlikely to be triggered by a person, but natural failures are very challenging to predict. Open glide cracks are a significant indicator, especially those that have opened recently, that those slopes may be imminent to avalanche.

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