In the past 24 hours, winds have averaged 15-25 mph with gusts to 50 mph at near- and above-treeline weather stations. These strong winds have been blowing from the west and northwest, loading easterly slopes near ridgelines and on the lee sides of prominent terrain features. That’s complicated the avalanche picture for today and tomorrow.
On some slopes, these freshly-formed wind slabs can be a danger in their own right. That’s mostly steep, east- and southeast-facing slopes above treeline, where the drifted snow fell on recent snow instead of bare ground. Similar conditions may exist on isolated northeast slopes and on the same aspects near-treeline. In this terrain, you can trigger slabs of drifted snow one to two feet thick. Avoid slopes steeper than about 35 degrees where you see dunes or find dense deposits of cakey, drifted snow.
On northeasterly slopes, the Wind Slab avalanche problem may overlap with a more widespread Persistent Slab avalanche problem. Where the winds deposited snow on slopes that harbor old, collapsible snow near the ground, the drifted snow is increasing the likelihood and potential size of triggered avalanches. The layer of old, faceted snow was the failure plane for a spate of natural and triggered avalanches when it was buried by heavy snowfall Friday. In some cases, the crowns ran long distances and connected across terrain features. People reported some slopes failing remotely, resulting in one very close call. In that incident, the two riders triggered a slope above them, but safe travel protocols - riding one at a time - kept the avalanche from having far more serious consequences.
The danger posed by the Persistent Slab avalanche problem will linger, especially on slopes where it is exacerbated by the wind-loading of the past 24 hours. Be on the lookout for steep slopes where the snowpack is deep enough and continuous enough to cover ground features. Carry avalanche rescue gear, rely on safe travel protocols, and look for obvious signs of danger, like collapses and shooting cracks. Follow those practices even on trips up closed ski areas, where there’s been no mitigation on slopes that are steep enough to slide.
Thanks to everyone who's contributed observations so far this winter. Special thanks to people who reported unintentionally triggered avalanches and/ or close calls. These are invaluable to other backcountry travelers, and they help us to confirm or fine-tune our forecasts. If you're out and about, please let us know what you see. It doesn't need to be dramatic or technical; just report some basics information about where you went, what kind of slopes you rode, and what the snow was like. Alerting us to any recent or triggered avalanches can be especially helpful.