Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Likely
- Size
- 2.5–3.5
Recent avalanches: There was a large natural avalanche yesterday afternoon on the south side of Tincan in the Library.There was a very large natural avalanche cycle last Thursday through Friday that included many of the mountains throughout our forecast zones. Natural avalanches also occurred on Saturday in the Turnagain Pass area. Although most of these avalanches were impressively large, the biggest was on the Widowmaker path on the backside of Seattle Ridge.
There is a very weak layer of snow buried 2 to 4' deep throughout zones. Because this weak layer is so sensitive in places, it could be triggered from flat terrain below a steep slope. This is an unusual set-up especially for Turnagain Pass, Girdwood, and Seward, which typically have a stronger snowpack. Yesterday, an observer noticed obvious signs (red flags) that the snowpack is still primed to avalanche, which included a natural avalanche and whumpfing. Temperatures were above 32° F yesterday in the alpine and remained above 32° overnight, which is another red flag. All of this is clear information that the snowpack needs more time.
This is a frustrating problem to be dealing with and the weak layer is going to take time to strengthen. The best way to completely avoid this problem is to stick to simple terrain (check out the ATES map for a route planning tool). Simple terrain is less than 30°, is not connected to steeper slopes above, and doesn't have terrain traps like gullies below. If you are heading towards steeper terrain, choose a low angle approach, travel one at a time on steep slopes, and be ready to rescue.
