Sawtooth & Western Smoky Mtns

Natural and human-triggered wet avalanches are likely where the sun and warm temperatures turn the snow surface to mush. Stability will deteriorate on very steep, sunny slopes first, followed by more shaded middle and lower elevations during the heat of the day. Triggering a large avalanche remains possible where the wind has stiffened the snow on more shaded, cooler slopes at middle and upper elevations.

WET AVALANCHE CONCERNS

It's Day 3 of an extended warmup. Here are some wet avalanche scenarios you need to consider:

Thin Wet Loose Slides: These avalanches are commonly small (photo). They are not likely to bury you but can sweep you off of your feet and carry you where you don't want to go. They often originate near warm cliff bands and rocks on very steep slopes that directly face the sun. They are most prevalent in the Smokys, White Clouds, Sawtooths, and near Banner Summit where there's more recent soft snow at the surface. We've observed dozens of these slides in the past few days across all forecast zones. While the "prime" locations for these avalanches have flushed, I'd expect to see a few more of these today. 

Gouging Wet Loose Slides: These large wet avalanches are more likely today. Mild overnight temperatures mean any crust you find this morning is likely to be thin. Hiding below the crust is a goopy mess of wet, unfrozen snow. The deeper this layer of wet snow gets, the larger the potential slide. Thin wet loose slides that originate at upper elevations can tap into deeper wet snow as they cascade down warm mid-elevation slopes (photo). Where the snowpack is less than about 2 feet thick, some slides could involve the entire snowpack. These avalanches are most likely on very steep, rocky slopes that are sheltered from the wind.

Wet Slabs: Ben spotted a wet slab avalanche yesterday on an E/SE-facing slope at 9,700' in the Boulder Mtns. It was a large, destructive slide that broke over 300' wide (photo). Wet slabs occur when meltwater pools and spreads along a weak layer in the snowpack, weakening the bond of the overlying slab. These slides are notoriously difficult to predict. Their occurrence depends on several variables that are unknowable on any given slope. However, we do have the main ingredients for a wet slab avalanche problem; defined weak layers of snow and plenty of meltwater production. It's not uncommon to see loose avalanches "flank out" or widen to release a wet slab lower on a slope. Today is only Day 3 of a prolonged warmup. This problem will remain an uncertain undercurrent as long as the snowpack remains mostly wet. 

Cornices: Large cornices sit atop many steep, alpine ridgelines (photo). Cornice failures are likely in the next few days as warm temperatures cause these features to sag and break. Give cornices a wide berth and limit the time you spend below them. While dangerous in their own right, a tumbling cornice may trigger one of the avalanche problems described above. 

It's important to address the uncertainty associated with forecasting wet snow avalanches but rather than getting lost in the weeds let's take stock of what we know. We have several factors going against us: record warm temperatures, long hours of hot spring sun (high sun angle), consecutive weak freezes, progressively more water in the snowpack, persistent weak layers and crusts that can pool meltwater, and lots of faceted snow that can quickly turn to mush. All of these factors get worse in the next few days but it's hard to know when/if the mountains will come completely unglued. Unfortunately, the only way to manage uncertainty is avoidance. It's going to get harder and harder to find consistently dry and/or supportable snow without wallowing in slush back to the car. Let the heatwave run its course, be conservative and give yourself options (BBQ at the tailgate sounds appropriate) if you miss your window.