Avalanche forecast

Silver Valley & Bitterroot Mountains

Idaho Panhandle Avalanche Center
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Avalanche danger

Sat
Alpine
1 · Low
Treeline
1 · Low
Below
1 · Low
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Highlights

Mild temperatures, minimal loading, and generally calm conditions this week have contributed to a stable snowpack. Wednesday night did see enough wind from the Northwest to transport snow onto slopes that may not usually load from our prevailing Southwest winds. Although wind slabs have had a few days to stabilize, continue to approach wind loaded terrain with a healthy sense of skepticism. Even relatively small wind slab avalanches formed in steep start zones or convex rollovers can sweep you off your feet, into terrain traps, or over cliffs. Continue to exercise normal caution: Travel one at a time through and under avalanche terrain, and pick safe snacking spots.

Avalanche problems

  • Wind Slabs

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

    Surface snow has remained light and fluffy, meaning it has been available for wind transport. Winds out of the NW of up to 20mph Wednesday night may have loaded slopes on SE aspects, that do not usually get loaded from our prevailing SW winds; as well as our usual wind loaded terrain on NE aspects.  These slabs have had a couple days to bond, but may still have the possibility to be triggered and would be dangerous in steep (>35 degree) open slopes.

Avalanche Discussion

Yesterday we toured in the Moon Pass area. Sun and blue skies made for a glorious day to be in the mountains. These favorable conditions should prevail until precipitation is forecast to move into the area on Sunday.

While out yesterday we took note of two layers that could influence our avalanche conditions moving forward. The first is the mid-January rain crust buried 15-20cm from the surface. While we found no propagation across our Extended Column Test, we did see some reactivity both above and below this layer. We need to keep an eye on this layer to see if faceting continues around it and how it reacts to loading from the snow forecast to begin Sunday.

The second layer of interest is the growth of surface hoar. The clear nights we have had in the mountains recently have allowed heat in the snowpack to radiate back into the atmosphere. The resultant cold snow surface freezes water vapor from the relatively warm air above it into delicate feather like crystals called surface hoar. Around Moon Pass we found these had grown all aspects, some as large as 2cm. If this layer gets buried intact, before it can be knocked down by direct sun or wind, it will become a dangerous persistent weak layer that can lay dormant for weeks or months. This is most likely to happen on North aspects, sun shaded, and wind sheltered but open terrain.

In the coming weeks, keep an eye on these two layers to see if they persist and how they react to new snow loading. In the meantime enjoy the spring like conditions.

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