Avalanche forecast

Bitterroot

West Central Montana Avalanche Center
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Avalanche danger

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

Triggering a larger avalanche on buried persistent weak layers remains possible. This is most likely in upper elevations where the snowpack has remained dry through the recent warm weather. Red flags like cracking, collapsing, and whumfing will not be obvious before an avalanche fails.

If we receive the higher end of the forecasted snowfall totals today, new snow avalanches are possible. Look for red flags like cracking in the new snow. If you encounter this, step back your terrain selection to avoid avalanche terrain.

Avalanche problems

  • Persistent Slabs

    • Alpine
    • Treeline
    • Below treeline
    Likelihood
    Possible
    Size
    1.5–2.5

    Triggering a large and destructive persistent slab avalanche is possible at upper elevations on north aspects and in isolated areas at mid elevation where the snowpack is deeper. The primary layer of concern is facets in the lower third of the snowpack. 

    You are most likely to encounter and trigger an avalanche on this problem in areas where the snowpack has remained dry and no melt-freeze crust exists at the surface. Avalanches will be much less likely on south and west aspects where the top portion of the snowpack has been wet and will freeze into a supportable crust by the end of the day today. 

    The sensitivity of this problem has decreased, but the consequences of any avalanche triggered are high. You will not see obvious red flags before an avalanche fails. The best way to identify the problem is to dig in the snowpack and look for poor structures with a firm slab on top of weak, unconsolidated snow. If you find this, individual risk tolerance will dictate how steep of a slope you are willing to expose yourself to, but if you want to avoid the problem, avalanches are unlikely on slopes 30 degrees or less.

    Large natural slab avalanche in the Swan Range, just north of the forecast area.

  • Storm Slabs

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

    Storm slab instability will rise through the day as the new storm arrives. Avalanches will be small but have the potential to run far and fast on a firm bed surface. 

    Cracking in the new snow and recent avalanches indicate that enough snow has fallen to tip the scale toward avalanches. To manage exposure, use slope angle and good sluff management. Avalanches are unlikely on slopes under 30 degrees. 

    Example of storm slab starting to show signs of cracking.

Avalanche Discussion

Today's forecast contains some uncertainty about where the rain/snow line will fall. Last night, the storm underproduced with just an inch or two of new snow.  If the rain line stays high and we receive just a few inches of snow today, avalanche danger will trend toward low. If we receive the forecasted 5-7 inches of new snow, new snow avalanches will be likely.

What happened to the wet snow problem? Low and mid elevation snowpacks have melted to the point where there is no longer enough snow to produce widespread avalanches, even with a rain on snow event. Wet snow avalanches are now very isolated in their distribution to only pockets of lingering snow at these elevations. 

We have reached the point with the persistent slab problem where slope angle and exposure are a matter of personal risk tolerance. Although triggering an avalanche is trending toward unlikely, any avalanche triggered could be large and unsurvivable. 

Statistics show that avalanches are most likely on 38-degree slopes. Should you stick to 30-degree slopes or 35 if you find poor snowpack structure? Studies have shown a range of a few degrees of error when people measure slope angle. People can think they are on a 35 degree slope when they are at the bullseye of 38. Our advice is that avalanches are very unlikely on slopes under 30 degrees. If you find a slab over persistent weak layers and want to avoid the avalanche problem completely, stick to slopes 30 degrees or less.

Please let us know what you see in the mountains today, especially regarding new snow totals and the rain/snow line. 

Ski and ride safe. 

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