Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Certain
- Size
- 1.5–2.5
Many steep slopes are near or at their tipping point. The mountains could come unglued tonight. Large, destructive avalanches will release naturally on some slopes. Triggering avalanches on steep slopes is a near certainty. Avalanche crowns have the potential to pull into "normally safe" 25-30 degree terrain.
The mountains received 2.5-4 inches of water (2.5-4 feet of snowfall) in the past 4 days, and we're looking at another 0.8-2 inches of water (8-20 inches of snowfall) by tomorrow morning. Precipitation rates—and the avalanche danger—are expected to peak tonight into Wednesday morning, while winds blow at moderate to strong speeds and temperatues remain near or just below freezing.
The intense multi-day storm is overwhelming very weak snow that formed during the month long drought, including surface hoar, facets, and facet + crust combinations. These layers exist on many slopes, the weakest of which are found at middle and low elevations. Before the weak layer was buried, it appeared to be one of the worst we've seen in recent years.
Heavily wind-loaded slopes are capable of producing avalanches that run "full track" to the valley floors.
The travel advice is simple: stay off of steep slopes and the areas beneath them.
Additional Discussion - Rain: Rain will fall at lower elevations and possibly as high as 7000' through Wednesday morning, triggering natural wet loose avalanches. Some natural wet slab activity is possible. If you're walking the dog in the rain, stay out from under steep slopes. The wet avalanches will not be as large as the persistent slabs releasing in middle and upper elevation terrain, but rain-on-snow avalanches are unpredictable and will be big enough to bury or injure people.
(2/2/2025) Debris from a large natural avalanche in the Warm Springs Ck drainage near Frenchman Bend.