Soldier & Wood River Valley Mtns

Today's winds are building dense slabs in exposed, upper elevation terrain and adding weight to the weak snow underneath. You're most likely to encounter enough snow for avalanche problems in the mountains on the western side of this zone (the Soldier Mountains and the mountains above the South Fk of the Boise River). If you're headed for these areas, refer to the Sawtooth and W Smoky Mtns Forecast. Much of this zone lacks enough snow for significant avalanche problems. Daily Avalanche Forecasts with danger ratings will begin when snow coverage increases. 

The main driver of avalanche activity this season is a layer of weak snow near the ground. This layer exists on all upper elevation slopes and most middle elevation slopes that face away from sun (northern half of the compass). Continued reports of large collapses in the snowpack are a clear indication that this weak snow is still a problem. Here's a look at how this setup varies across our region:

WETTER AREAS: the mountains in the northern and western portions of our forecast area (Banner Summit area down through the Western Smokys) have been favored by recent storms. Here, you'll find dense, 2-3+ foot thick slabs sitting on top of the very weak snow underneath. While the thickness of this slab makes it slightly more difficult to impact the weak layer underneath, continued reports of large collapses in the snowpack are a clear indication that this weak snow is still a problem.

DRIER AREAS: Recent storms have largely skipped over the mountains in the eastern and southern portions of our area. Here, the slab sitting on top of the early-season weak snow is in the 1-2 foot thick range. Initially, we needed the stiffening and loading effects of the wind to have avalanche issues, but this slab is becoming thick enough to produce avalanche concerns even in areas sheltered from the effects of the wind. 

A storm impacts the region today, adding complexity to this picture. Winds have been blowing at loading speeds for over 12 hours and will continue to blow as the snow falls today. The dry areas described above may only pick up a few inches, while the wetter areas may see as much as 12" with average totals in the 4-8" range. The wind is redistributing large amounts of snow today, building fresh slabs that will be reactive to your weight. Importantly, these slabs are adding weight to the weak snow at the base of the snowpack, increasing the likelihood of triggering a large, persistent slab avalanche. Smaller triggered wind slabs can be very effective triggers for weak layers deeper in the snowpack.

Before committing to avalanche terrain, take an honest account of your understanding of the early-season snowpack. Travel through the mountains knowing that triggering large avalanches is uncomfortably likely today. Pay attention to the terrain you are traveling through and the terrain above you. Large avalanches can be triggered long distances away from the slope that avalanches. Smaller wind slabs will be failing naturally and can act as triggers for large, more dangerous avalanches. 

Watch Brooke's Weekend Update to get a sense for what's been happening in our snowpack.