Bitterroot

Avalanche problems

• 

  Wind Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Wind slabs are possible at upper elevations and along ridgelines. These wind slabs are now 24-72 hours old and becoming increasingly stubborn. If you encounter an area with newer wind slabs, expect these to be more sensitive and likely to avalanche. Natural wind slab avalanches are now unlikely.

  The wind slab problem primarily exists in the northern Bitterroot, Rattlesnake, and Seeley zones. Pockets of wind slabs are in the central and southern Bitterroot, but these areas did not see the aligned west wind that hit terrain further to the north last weekend and early this week.

  Wind slabs can often be identified by their smooth, rounded appearance and form along ridgelines, in gullies, behind rocks, or on convexities. 

  If you encounter cracking around your skis or snowmobile or see recent wind slab avalanches, step back to terrain with a slope angle under 35 degrees. 

   

  

• 

  Loose Wet

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Possible

  Size

  1–2

  Despite cooler temperatures today, expect the snow to warm with the strong solar input and lack of wind cooling it off. When the snow becomes wet this afternoon, human-triggered avalanches are likely, and natural avalanches are possible.

  The timing of wet snow is highly dependent on the refreeze last night. Most solar-affected areas got damp or wet yesterday, and it froze back up last night. Today, that crust must break down before the snow can lose strength and lead to wet loose avalanches. If you find yourself in an area with strong sun holding fresh, dry snow, expect the snow to become wet quicker.

  The typical progression of wet loose avalanches goes rollerballs, then to small point releases off rocks, trees, cut banks, and in start zones, and then to larger wet loose avalanches. If you encounter rollerballs or small wet loose avalanches, expect larger ones to follow.

  If you find yourself in wet, unsupportable snow or see natural, wet, loose avalanches, it is time to step back out of avalanche terrain and be aware of what is above you.

• 

  Persistent Slabs

  N

  NE

  E

  SE

  S

  SW

  W

  NW

  • Alpine
  • Treeline
  • Below treeline

  Likelihood

  Unlikely

  Size

  1.5–2.5

  Triggering a larger persistent slab avalanche is unlikely today, although the poor snowpack structure and ingredients for a larger avalanche remain. The two primary layers of concern are small facets surrounding a crust in the middle of the snowpack, and lingering facets near the ground.

  These layers had a good test last week, with over an inch of water weight falling on them. By now, the weak layers have adjusted to that additional load, and we have not seen an avalanche on these layers in a few days.

  To our east, outside the forecast area, a snowmobile triggered a persistent slab avalanche adjacent to a near-miss avalanche from January. This area has a shallower, more continental snowpack but is worth noting if you are recreating in the Skalkaho Pass area.

  You are unlikely to see signs of instability like cracking or collapsing before triggering an avalanche.  Smaller avalanches, such as fresh wind slabs described above, can step down and trigger a larger avalanche on persistent weak layers.

  Dig down into the snow, and if you find softer snow around hard crusts, or loose sugary snow below a firmer slab, recognize the potential for a large and dangerous avalanche. Reduce your exposure by sticking to slopes without rollovers or convexities and free of terrain traps or use slope angle to avoid the problem altogether by sticking to slopes less than 30 degrees.