Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Almost Certain
- Size
- 3
Large, long-running, and destructive natural avalanches are ongoing this morning! Layers of weak sugary snow or facets and feathery surface hoar developed during the prolonged December dry spell on and near the snow surface, and the snow in shallow areas became loose and sugary all the way to the ground. As new snow and drifting snow overload slopes plagued by the widespread persistent weak layer, avalanches are becoming increasingly likely. Today, natural and human-triggered slab avalanches will be large, destructive, and life-threatening.
- Avalanches could be triggered remotely, from a distance, or worse, from below!
- Collapsing or whumpfs and shooting cracks indicate unstable snow.
Wind-drifted snow now overloads slopes with poor snow structure, and large avalanches of wind drifted snow failing on the December persistent weak layer are likely. Watch for and avoid stiffer drifted snow on the Lee side of prominent ridges and in and around terrain features like sub-ridges, gully walls, mid-slope rollovers, and cliff bands.
People should avoid being on and under drifted slopes at all elevations today.
As new snow stacks up it is overloading slopes plagued by persistent weak layers that are widespread and exist at all elevations across the zone. Natural soft slab and loose avalanches of new snow are very likely today on slopes steeper than 30°, even in lower-elevation terrain.
Natural avalanches are occurring, and people are very likely to trigger avalanches at all elevations in the backcountry,so be careful where you walk the dog or build a snowman, and avoid fishing beneath steep slopes with lots of new snow. In fact, people should avoid playing, walking, running, or biking on or under all steep slopes, even those in the foothills!