Weak layers near the bottom of the snowpack make it possible to trigger a big persistent slab avalanche. Additionally, a few inches of recent snow has been drifted into fresh wind slabs that are possible to trigger. Remain cautious of big open slopes where a persistent slab could be triggered from a shallower spot and break deep and wide. Steer clear of freshly drifted slopes, especially in terrain where a slide could have big consequences, like above cliffs, trees or gullies.
This problem will be more likely at upper elevations, but the weak layer can also be found at mid elevations and it is worth digging down to evaluate it.
Dangerous avalanche conditions exist near Island Park, West Yellowstone, and in the southern Madison and southern Gallatin ranges, and the avalanche danger is CONSIDERABLE. These areas have a snowpack with buried weak layers that produced big avalanches over the last couple weeks. New snow and wind are adding weight to the snowpack, increasing the chances for a person to trigger a big persistent slab avalanche today. Ian was in the Lionhead area on Friday where he saw evidence of many recent large avalanches (video, observation). Yesterday I went to Taylor Fork and saw a similar snowpack which has also produced big avalanches (video, observation). The new snow and wind alone are enough to create fresh wind slabs that can easily be triggered and may be large enough to bury or injure a person. Choose routes that avoid slopes steeper than 30 degrees, and be cautious of flatter terrain directly below steep slopes.
Near Cooke City, and in the northern Madison and northern Gallatin Ranges, weak layers near the bottom of the snowpack make it possible to trigger a big persistent slab avalanche. Avalanche danger is MODERATE in these areas. Although persistent slab avalanches have become less likely, their size could be many feet deep and hundreds of feet wide with potentially unsurvivable consequences (last Monday’s avalanche on Chimney Rock is an example). Additionally, a few inches of recent snow has been drifted into fresh wind slabs that are possible to trigger, similar to a wind slab avalanche triggered by skiers yesterday on Mt. Blackmore. Remain cautious of big open slopes where a persistent slab could be triggered from a shallower spot and break deep and wide. Steer clear of freshly drifted slopes, especially in terrain where a slide could have big consequences, like above cliffs, trees or gullies.
In the Bridger Range avalanches are unlikely and generally safe avalanche conditions exist. Over the last couple days, moderate to strong winds drifted a few inches of recent snow into small wind slabs (obs. from northern Bridgers), and a few small fresh slabs may form with today’s wind. These will be generally small and should stabilize quickly. Remain alert for small unstable drifts if you are riding or skiing in terrain where a small slide would have big consequences. Avalanche danger is LOW in the Bridger Range.
