Persistent Slabs
- Alpine
- Treeline
- Below treeline
- Likelihood
- Possible
- Size
- 2–3
Last week's snowfall and wind added a significant amount of new load to the snowpack—especially in the Soldier Mountains— and our persistent weak layers are now buried 2-3 feet deep. While less natural activity occurred in this zone compared to further north, several significant slides were observed—including these large ones on Peak 1 in the Soldiers.
The lack of snowfall and significant wind the last few days have provided our snowpack a much-needed breather. However, we're about to poke one last sharp stick in the eye of the persistent slab problem. Today will be by far the warmest and sunniest day since the start of the January 10th storm cycle. To reduce the likelihood of triggering a persistent slab avalanche today, I'd recommend three things:
- Choose moderate slopes with low consequences. With a persistent slab problem, this is our primary line of defense.
- Avoid slopes with evidence of recent or past wind drifting. Wind loading may have created a dense slab atop the weak layers. This is especially the case in the Wood River Valley, where less snow fell last week and any sort of slab is uncommon outside of wind-affected areas.
- Avoid slopes that are facing the sun today. The warming temps and sunshine may be adding more stress to buried weak layers.
ADDITIONAL DISCUSSIONObservers in upper elevation terrain continue to report that wind slabs are becoming less reactive. This doesn't mean you should stop monitoring the effects of wind as you travel. As discussed above, you’re more likely to trigger a persistent slab avalanche where a stiff, wind-loaded slab sits over buried weak layers. Last Thursday, we found this type of snow structure during our site investigation of the fatal avalanche that occurred Wednesday in Baker Creek (see video at right, more details in the Forecast Discussion below).