The last major storm exited the region on Thursday night leaving large amounts of snow available for wind transport at all elevations. And that’s exactly what the strong winds yesterday did: move snow across ridgelines and pack it into touchy wind slabs up and down the range. With cold temperatures overnight, these recently formed slabs may still be sensitive enough for human triggering today, especially in steep alpine terrain. With the wind blowing snow into the evening yesterday, some of these wind slabs are expected to be large. We have one report of a very large natural wind slab avalanche on Mt. Wood, and many small natural avalanches in the southern half of the range, that may have occurred from the wind loading yesterday. Triggering these slabs will be most likely where they are thinner or softer: below cornices, the sidewalls of chutes and gullies, and near convexities. One such slab was triggered remotely yesterday afternoon on the Chicken Wing. As the recent wind slabs begin to bond, new sensitive wind slabs may form by this evening. Especially in the northern half of the area where the potential for a few inches of snow are forecasted to fall this afternoon. That will give SW winds more ammo to continue loading leeward slopes. In situations like this, where wind slabs could be large, and may be found with varying levels of sensitivity, cautious route finding and conservative decision making is required to manage the hazard. Pay attention to where snow has recently drifted, or is drifting anew. Hollow sounding snow, or cracking around you means that you may already be standing on wind slabs touchy enough to trigger.
Snowpack tests in Mammoth and June show that the storm slabs from 3/21-22 are beginning to settle down and become less reactive in most areas. As the snow becomes more supportable and less likely to avalanche, it will also be harder to trigger the deep persistent layers buried about 2m under the surface. That’s good news. The likelihood of you triggering the deep facet layers is very low. But the possibility of a wind slab avalanche running down and stepping down into an area where these layers are still weak is not out of the question. The resulting slide would be deadly and so it is not a scenario that we’re comfortable ruling out just yet. You can use your probe to feel down into the snowpack and see if there are less resistant layers lurking under your feet. You’ll probably find them above 9,000’ on W-N-E facing slopes. They’ll be a little closer to the surface (and thus slightly easier to trigger) in areas that received less snow during the last storm cycle. Managing the wind slab problem to avoid a smaller avalanche running down over these layers, and becoming much larger, is a good way to avoid triggering the deep slabs. Other large triggers, like a snowmobile landing a jump in just the right spot, are also more likely to result in a very large slide.