Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 1–2
A well-identified weak layer (buried surface hoar) is down about 2' at mid-elevations and found just above a prominent crust (2/13) in the upper snowpack. This layer was found on shady aspects in the Hurricane Ridge area including near ridgelines and also in snow pits near Mt Ellinor. A sensitive snowpack with collasping and whumpfing was observed in the Hurricane Ridge area earlier in the week, but not on Thursday.
We have limited information about a known weak layer in the upper snowpack, at depths that a human traveller can affect and deep enough to potentially lead to a large and dangerous avalanche. This layer may have become less likely to trigger over the week based on limited information from area snowpack tests.
Treat all open steep slopes as suspect until proven otherwise, especially shady aspects where surface hoar was more likely to have survived and buried intact. If you experience any collapsing or whumpfing, remotely trigger avalanches, or see other signs of instability, retreat to simple, lower-angle terrain.
Persistent slabs are notorious for surprising backcountry travelers; they break more widely across the slope and can be triggered from lower-angle terrain than run-of-the-mill storm slab avalanches. Dig and look for the buried surface hoar to help rule out slopes, and consider using snowpack test to gain more information, but do not use inconclusive results to deem a slope "safe" or not.
(2/26/2026)
A propogation saw test (PST) result of 79/100 End on a N aspect near Steeple Rock. This snowpack test gauges the likelihood of a fracture to propogate on a known weak layer (buried surface hoar). Numbers below 50 and indidcate a higher likelihood of fracture propagtion.
Snowpack tests like this can be helpful for identifying which slopes to avoid, but are only one piece of information from one location. They should not be used to deem a slope "safe".
Photo: Sam Luthy - NPS