Avalanche forecast

Rattlesnake

West Central Montana Avalanche Center
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Avalanche danger

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

Lingering pockets of buried surface hoar make it possible for skiers and riders to trigger a persistent slab avalanche above 7000'. The chance is higher in the east Rattlesnake. Reduce the possibility by avoiding convexities and slopes over 35º, especially on shaded north slopes. Below 7000' warm temperatures have created crusts that reduce riding quality, and limit avalanche potential. 

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1–1.5

    The primary concern in the Rattlesnake is a layer of buried surface hoar 6"-8" below the surface. Reactivity of this layer is rather patchy, with no results or instability noted in the West Rattlesnake outside of Snowbowl over the weekend and a skier triggered slide reported at Wisherd ridge on Sunday. The layer can be found throughout the zone. Slides on this layer will most likely be small and are unlikely to bury a person unless a terrain trap like a gully is involved. It is certainly deep enough to take you for a ride and rake you through trees or over a cliff. 

    You are most likely to find this buried surface hoar above 7000' and northerly aspects. The best way to manage it is to avoid slopes and convex rolls over 35º. If you choose to ski steeper terrain, carefully assess the snowpack for a lower-density stripe of buried surface hoar. Use small, safe, and representative convex rolls to test the reactivity of the layer to skier travel. Avoid traveling in or above terrain traps. 

    (1/15/2023)

    Skier triggered avalanche on Wisherd Ridge

  • Loose Dry

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1

    It is possible for skiers and riders to trigger small wind slab on easterly slopes at upper elevations in the Rattlesnake today. These will be small, likely less than D1, but enough to carry you into hazards. 

    Avoid wind loaded pockets greater than 35º just below ridge line in upper elevation terrain today.

Avalanche Discussion

Overall the avalanche hazard is trending lower. Mild temps, calm winds, and isolated new snow have contributed to a mostly stable snowpack, with the exceptions noted above in the problems. Most notable is the surprise overproducing storm that hit the northern Bitterroot. Elsewhere, there is just enough reactivity and uncertainty in the upper elevation layers to keep it at moderate. Buried surface hoar is a tricky one, the touchiness dropped considerably over the weekend in both the Rattlesnake and Seeley zone, but it's still down there waiting for someone to hit the sweet spot and trigger it. Basal facets in the southern Swans and Southern missions remain a slight concern that is an unlikely but still plausible and high consequence problem.   At least in the Rattlesnake, the basal facets have bonded and become unreactive, so we can remove them from the problems list.  

Throughout the forecast area, crusts extend to 7000' and lower the possibility of avalanches at mid-elevations. Despite the low hazard, exceptions exist, and avalanche conditions could be found. Continue to stay alert to changing snow conditions and red flags as you travel.

The lower elevation snowpack, unfortunately, continues to shink. In the central Bitterroot, slopes are almost bare to 6000' on the south aspects and 5300' on the north. Wet loose avalanches have been a concern for the past week at lower elevations. Today temperatures should be cool enough today to keep snow surfaces mostly frozen. The freeze-thaw cycle has reduced the likelihood of natural loose wet activity if it does warm up. You could kick off small loose wet on steep slopes if temperatures climb higher than forecast.

We received a lot of high-quality observations over the weekend. Thank you to those who sent them in. You can submit new observations here.

Ski and ride safe

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