Bitterroot

Triggering an avalanche on persistent weak layers is likely at upper elevations and possible at mid elevations. Human triggered wind slabs are possible along ridgelines on all aspects. 

 Avoid slopes over 30 degrees, and be aware of what is above you, as remote triggering is possible. Collapsing, whumpfing, and cracking are obvious signs of instability. 

East winds and warmer temperatures have been the story for the past two days. The low pressure system passing below us through Idaho has given us light ridgetop winds out of the east. With this came an increase in temperatures and low clouds. Cloud cover decreases as you move north through the zone, with Seeley lake having only a few lingering clouds yesterday. This system did not bring significant snowfall, with totals of only a few inches of snow and 0.1" to 0.2" SWE (snow water equivalent) since Saturday.  At Lost Trail Pass, dense fog and light winds warmed the snow surface Friday and Saturday but not enough to create wet snow avalanche activity.

This has done little to help with our snowpack, and we are continuing to deal with sensitive persistent weak layers. The two layers of concern continue to be the layer of buried surface hoar from late November on all aspects and depth hoar on northerly aspects. The natural avalanche cycle on these layers has paused for now, although any significant load will bring with it another natural cycle. 

Snowpit scores on these layers are increasing. Extended column tests (ECT) are not propagating across the column as readily, but propagation saw tests (PST) are still consistently failing to the end. Observers are reporting widespread collapsing and whumpfing. This highlights why putting too much faith in snowpit tests alone in light of obvious instability is a dangerous decision making trap. 

How much snow was available for transport by the east winds is highly variable depending on elevation and surface conditions. Wind slabs exist on north through east aspects from previous winds and, in some areas, may be hidden by new snow. In the Seeley lake area, new snow totals have been higher the past two days, and wind slab has formed on west aspects. The bottom line for the wind slab is to stay off any hollow feeling snow along ridgelines and avoid any visibly loaded features. 

Between 4000 and 5500’, avalanche danger is low, with the exception of the terrain around Lolo Pass, where pockets of increased hazard may exist in sheltered areas.

Conservative decisions are still necessary in the backcountry. As the slab above the persistent weak layers gains strength and avalanches become harder to trigger, it will become tempting to move out onto steeper terrain. Do not let a lack of unstable results in snowpits convince you to travel in avalanche terrain when the snowpack structure is still so poor. Any avalanche that does break will be large and destructive. 

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Ski and ride safe.