Silver Valley & Bitterroot Mountains

Be mindful of shallow, dense slabs of snow that have formed on top of weaker snow layers and a firm crust at upper elevations. Isolated areas directly below ridgelines and in steep gullies could harbor a stiff enough slab to fail with human disturbance and produce a small slide. Limit your exposure time in more complex terrain and run-out zones, and continue to use safe travel protocol in the mountains.

Today marks the first notable rise in avalanche danger that we have seen since the middle of January. Snowfall within the last week has been light and steady, but we have been incrementally loading very worrisome weak layers. Most notable is a layer of large, buried surface hoar that has been found on all aspects above about 5500 feet. This weak layer was initially buried by light snowfall on January 28th, and in many locations, the overlying slab has either lacked the cohesion or volume of snow to be capable of creating dangerous avalanches. We’ve been anxiously monitoring the weather and snowpack to determine when either of those variables will significantly change. Strong winds and continued snowfall last night are working to teeter us away from stability.

As the forecast team came together this morning to discuss our current predicament, certain realizations helped guide us towards today’s Considerable danger. We meet each morning prior to the forecast to share the things we are certain about, but we also have to acknowledge our uncertainties. To start, here’s what we know:

In the Silver Valley and Bitterroot Mountains, the danger remains Low. In part due to higher freezing levels, but mostly due to significantly less snowfall within the past week (Bitterroot Mountains Observation). Up north, we know that we’ve seen cooler temperatures and little bit more snow. We also know that the buried surface hoar appears to be almost everywhere above the recent rain/snow lines. Recent observations have uncovered very large feathers, intact and upright, having survived even in areas atypical like open slopes on the windward side of ridgelines, or directly on the ridgetops. We have found areas with more than a foot of recent snowfall burying this weak layer (Selkirk Mountains Observation). And lastly, we know from history that surface hoar is a weak layer that is not to be underestimated. Many avalanche professionals and recreationists alike have been involved in near-misses or accidents, where a layer of buried surface hoar collapsed and propagated an avalanche wider than expected or in a place where it was not known to exist. The signs of instability are not always there, and the potential consequence of a surprise can be severe.

Now here’s what we are less sure about: Is this weak layer as widespread as we think? It certainly seems so from recent observations, but it’s also important to note how few those observations are at times. Our forecast region encompasses thousands of acres and hundreds of mountains, and we are currently relying on weather data from a handful of remote stations and a grand total of 9 field reports since snowfall returned a week ago. The other uncertainty that we are grappling with is that we don’t have any field reports yesterday from the areas known to presently have greater overlying slab depths. That is the northern portions of the Selkirk Crest and parts of the West Cabinets.

Uncertainty can be a red flag in and of itself. Combined with the known concerns we have surrounding our snowpack structure, Considerable danger was, in some ways, an easy choice for the team this morning. We urge you to pay attention to exactly how much recent snow you are walking around or riding a machine on today. And take some time to slow down and confirm whether or not the recent snow is resting on top of large, buried surface hoar. It’s not very far down right now and the new snow is still relatively soft, so this can easily be done with quick hand pits as you move through the mountains. If you find this worrisome structure beneath you and stiffer slabs greater than 10 inches are present, we encourage you to do two things. First, steer away from slopes steeper than 30 degrees and avoid traveling near or underneath large, steep, open terrain. And second, consider dropping us an observation on the website or the Avy App to help us get a better handle on the distribution and sensitivity of our current avalanche problem. It takes a village to keep track of the conditions out here and we have greatly appreciated all the observations we’ve been getting thus far.

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IPAC is now on the Avy app! View, submit, and share observations on the go using the AvyApp. Your backcountry observations are critical for building our avalanche forecasts. Avy provides a centralized location for core trip planning, and you can view streamlined, up-to-date avalanche and weather forecasts for your selected zone, using offline caching. Download Avy today - App Store and Google Play.