Avalanche forecast

Avalanche forecast

Payette Avalanche Center
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Avalanche danger

Alpine
2 · Moderate
Treeline
2 · Moderate
Below
2 · Moderate
Out of date — this forecast expired 3 years ago. You’re viewing past conditions, not the current bulletin.

Highlights

Persistent slab avalanches are becoming unlikely. You are more likely to trigger a persistent slab in and around the West Mountain zone. South-facing slopes continue to harbor buried weak layers above melt-freeze crusts. 

Expect the avalanche danger to rise throughout the day as a storm moves into the region bringing siginificant snow and moderate south/southwest winds this afternoon.

Avalanche problems

  • Persistent Slabs

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

    There are persistent weak layers buried within the upper 1-2 feet of the snowpack. Buried surface hoar and small-grained facets were responsible for a snowmobile-triggered avalanche last Saturday (02/25) (pictured to the right). In the southern portion of the advisory area (West Mountain and Council Mountain), you are likely to find these buried weak layers on multiple aspects below 8000 feet. In the northern end of our advisory area (north and east of McCall), you're most likely to encounter buried weak layers on southern aspects, where facets have formed above melt-freeze crusts. 

    Overall, triggering a persistent slab avalanche is becoming unlikely. The likelihood of triggering a persistent slab avalanche is higher near the West Mountain zone. Digging into the snowpack is the only way to tell if buried weak layers are lurking. Even then, buried weak layers (especially buried suface hoar) can be spotty and difficult to find. Never base a "go or no-go decision" on one snow pit. The only sure way to avoid a persistent slab avalanche is to limit exposure on slopes steeper than 30 degrees.

    Additional Discussion: Snowfall accompanied by south winds are forecasted to increase today, especially in the afternoon hours. New snow and wind will be adding additional load to these buried weak layers. As the snowfall increases and the snowpack begins to endure more stress, dial back your terrain choices and give yourself space from slopes steeper than 30 degrees.

    (2/25/2023)

    This snowmobile-triggered avalanche was on an east aspect around 7600 ft. This avalanche failed on a layer of buried surface hoar and small-grained facets.

    Photo: Public

Avalanche Discussion

Today's avalanche forecast is sponsored by Mile High Powersports of McCall. Thanks for supporting the Payette Avalanche Center.

Within the past two weeks, we've seen light but consistent snowfall and cold temperatures. This weather pattern has been conducive for creating and burying weak layers. Intermittent snow showers with brief clearing periods (especially overnight) can create persistent weak layers. Light snowfall with light winds can quickly bury these weak layers. Small loading events of a few inches here and there can keep weak layers preserved just underneath the snow surface without much notice. Since these weak layers are within the upper 1-2 feet of the snowpack, they are subjected to large temperatures swings near the surface and therefore do not strengthen. On south-facing slopes, weak layers have formed above melt-freeze crusts. A trigger, such as a significant loading event or the weight of a large object (i.e. snowmachine) can be all that is needed to overload these buried weak layers and create an avalanche. The mountains are likely to see both of these natural and artifical triggers this weekend. 

There are four items to discuss with your travel partners to keep on your radar today:

  1. Persistent slab avalanches, will you be traveling in terrain where these are possible? If so, what is your plan to mitigate exposure to a persistent slab avalanche?
  2. Wind slabs, although unlikely, there may be some isolated pockets of wind slabs in terrain above 7000 feet, especially below ridgelines and on the leeward side of terrain features like gullies.
  3. Dry loose snow (sluff), 4-6 inches of light snow sits near the surface. In terrain steeper than 35 degrees, sluff management should be part of your travel plan.
  4. The incoming storm, a potent winter storm is forecasted to impact our region this afternoon into the evening. 6-12 inches of snow with moderate south/southwest winds are expected. Give yourself flexibility to change your plans if you notice the storm is increasing the avalanche danger.