Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2–3
What and where is it? Triggering a wide, 1-3 foot thick slab avalanche is possible in sheltered and wind-loaded terrain. Several days of heavy, dense snowfall, rain, and warm temperatures formed thick, meaty slabs on most middle and upper elevation slopes. Multiple crusts are buried in the upper 3 feet of the snowpack, providing possible failure layers for the slabs above.
How can you recognize it? Assume the slab + weak layer setup exists on all slopes. You may or may not experience obvious signs of instability—snowpack collapsing or cracks shooting out from your skis or sled—before triggering an avalanche.
How can you manage it? While a surprising lack of widespread snowpack collapsing or cracking yesterday indicates that the snowpack is adjusting to the huge load from the recent storms, triggering powerful avalanches is still on the table. As you change elevation and aspect or travel in different drainages, you'll see a lot of variability in the buried crusts:
- How many crusts?
- How thick are they?
- How hard are they?
- Did small facets form above or below them?
Unfortunately, accurately predicting which slopes are trouble and which are safe to ski or ride is challenging. You may be able to trigger avalanches remotely—from flat terrain below, above, and to the sides of steep slopes.
Additional Discussion: Weak, sugary, faceted snow in the bottom part of the snowpack is now buried 3-5 feet deep on W-NW-N-NE-E-SE facing slopes at middle and upper elevations. Triggering a huge slide on these layers isn't as likely, but the resulting avalanche would be unsurvivable. You're most likely to poke this beast 1) where the snowpack is less than 4 feet deep and 2) in windy and/or rocky areas where the snowpack depth is variable.
(12/20/2025) Large natural avalanche on Gladiator Peak in the Boulder Mtns.
