Persistent Slabs
- Alta quota
- Limite del bosco
- Sotto il limite del bosco
- Probabilità
- Possible
- Dimensione
- 2–3
The new year is ringing in with northeast wind blowing in the teens mph on the ridgetops this morning, but should start tapering by mid-morning to 5 to 10 mph. The wind has been blowing for 2 days and the addition of windblown snow to the top of the snowpack has added stress to several layers of buried weak snow above 2,500'. We don't know exactly how much weight it would take to trigger one of these slides, but there's a chance the weight of a human is enough, especially near a thin spot in the snowpack which is typically close to a rock outcrop. This problem may not give any warning signs, but a whumpf is the most likely red flag.
Wind Slab: The more likely, but less consequential problem today, is triggering a small wind slab that could be up to 1' deep in the upper elevations. Several human-triggered wind slabs were triggered yesterday in Turnagain Pass. The bigger concern with triggering a wind slab is that it may be enough weight to trigger a larger persistent slab avalanche described above. Before the wind started blowing, the snow surface was getting weak with facet and surface hoar growth. When a wind slab is formed on top of layers like this, it may be easier to trigger and the chance of triggering them could linger for days even if the winds calm down.
Cornice Fall: Cornices are likely to have grown over the last few days of windy weather. They can be tricky to see when approaching so it can be helpful to get a good look from down the ridge a ways. Cornices tend to break back further than expected so give them a wide margin if possible.
(12/31/2024)
Snow pluming off John Mountain from east winds yesterday.
Photo: Daniel Krueger