West Slopes South

Dangerous avalanche conditions are expected to develop in the West South zone this weekend. Strong winds, warming temperatures, and continued precipitation may overload a weak upper snowpack, resulting in both natural and human-triggered slides. Slopes may reach this tipping point at different times, so ease into terrain slowly as you keep an eye on rapidly changing conditions.

Avalanche Burial: At around 12:00 pm on Thursday, February 19th, a group of snowmobilers were riding near the Shoestring Glacier on Mt Saint Helens. On their second pass across a slope, two riders were traveling together when they triggered a large avalanche. Unknown to the first rider, the second was fully buried by the slide. Once realizing their friend was missing, the team quickly initiated an avalanche rescue. They located the buried rider with an avalanche transceiver and a probe strike. When they initially reached his airway, he was purple and not breathing. After several rescue breaths, the rider began breathing on his own and eventually regained consciousness. The buried rider was able to ride out under his own power with no injuries. Avalanche: HS-AM-R2-D2-U, NE, 6000 ft.

Well, if that doesn't catch your attention, I'm not sure what will. Conditions are changing in the West South zone as a major wind event and continued snowfall on a warming trend begin on Saturday. Winds will be coming from the east/southeast, meaning areas closer to the crest will likely see stronger wind speeds than what is forecast in the mountain weather forecast. With east wind events, you can expect to find slabs forming on atypical aspects or lower in the terrain than you are used to. 

Whether by wind or heavy snowfall, any slab that develops will rest over a weak upper snowpack. You'll find facets, surface hoar, and weak crusts all within the top 3 feet of the snowpack, which is the generally accepted depth a human can influence. Most of the week, the snow above the 2/7 has been light and fluffy, resulting in minimal reported avalanche activity. However, the involvement on Mount St. Helens is a reminder that not all areas in our large zone contain the same conditions and that consequential avalanches can occur at any hazard rating. 

Moving forward, we expect conditions to begin to change. This is not your typical Pacific Northwest snowpack structure, so you shouldn't treat it as such. Buried surface hoar at the 2/13, faceting around the 2/7, and low-density snow are all weak grains waiting to be capped by a heavier load. Don't roll out your typical playbook and expect that everything will be fine. Tune your senses into what the upper snowpack and weather are telling you wherever you're recreating and then choose appropriate terrain based on those observations. Whether these weak layers start to rear their ugly heads on Saturday or not for a few more storm days remains to be seen. But the structure is there, we're just waiting on the when, not so much the if.

Most low-elevation terrain lacks the snowpack and general exposure to wind to pose much avalanche hazard on Saturday. At all elevations, travel hazards are still a challenge. Open creeks, holes, and shallowly buried rocks and stumps are widespread throughout the mountains. Some of these hazards were easy to identify last week, but are now hidden under a few inches of new snow.