Benjamin Spillman, Reno Gazette Journal
Unusual snowpack conditions in the Sierra Nevada are contributing to a type of avalanche problem that in the past decade has rarely been widespread in the region.
That’s according to the Sierra Avalanche Center, a non-profit organization that partners with the U.S. Forest Service to observe and analyze snow conditions in the Lake Tahoe area and beyond.
“There could be avalanches in places that have never seen avalanches before,” said Brandon Schwartz, lead forecaster for the center.
The biggest contributor to unstable conditions is buried surface hoar which leads to persistent slabs.
Surface hoar is a type of frost that forms on top of the snow. Typically in the Sierra Nevada the frost doesn’t last long before warm temperatures or strong winds break it down.
But this month, in certain locations across the forecast region, the frost managed to survive subsequent snowstorms. That means it’s buried now and forming weak layers that can break and create slab avalanches.
Schwartz said in the past 12 seasons widespread buried surface hoar conditions have only occurred three times. This season it’s already happened four times. In the Sierra Nevada it’s much more common to encounter avalanche problems related to storm and wind loaded snow.
“(Surface hoar) is generally destroyed by wind and warm temperatures leading up to the next storm,” he said. “(Recent storms) have come in with less wind and colder temperatures.”
Schwartz said the reason it’s important to be aware of the condition is because it’s so unusual for the Sierra Nevada.
Backcountry clearings below treelines, which are often the types of places skiers, snowboarders and snowmobilers love to ride, are where the persistent slabs are forming.
“The backcountry public needs to approach differently and manage terrain differently when dealing with this type of weak layer,” Schwartz said.