This past week's persistent slab avalanches were triggered on a layer of buried surface hoar or on a layer of small, faceted crystals buried 2-4 feet deep. This layer is widespread in the Ogden area mountains though there are some places where it was destroyed prior to the storm. The buried surface hoar is most dangerous where it was sheltered from the wind and buried intact. It might catch you off guard as you descend into sheltered, lower and mid-elevation slopes or gullies. Though observers near Ben Lomond noted its presence Thursday and were unable to get propagation while performing stabiity tests, this type of weak layer is deceptive and takes a while to strengthen.

Because this weak layer can be coy, your best bet for finding it is to dig about 4 feet deep, perform stabilty tests like the ECT, and make sure it doesn't exist. Buried surface hoar does not behave like a typical weak layer so a lack of cracking, collapsing, or other obvious signs of instability does not mean slopes are stable. Tracks from other people are also not a guarantee of stability. If you are not interested in digging then the easy solution is to avoid being on, connected to, or underneath slopes steeper than 30 degrees.

Left: Observed buried surface hoar near Rodeo Ridge was unreactive to stability tests Thursday. (pc:M. Henderson)

Right: One of numerous avalanches failing on buried surface hoar or small facets on Monday in the Cutler Ridge area. (pc: B. Brandt)

There is plenty of snow available for transport and wind drifts should be considered suspect and avoided in steep upper elevation terrain. Drifts often appear rounded, scalloped, or otherwise textured and form in the lee of terrain features such as rocky outcrops and sub-ridges. These drifts may be more sensitive than usual as some of them may be siting on small surface hoar or granular faceted snow formed Thursday night.

Cold, dry snow under the heat lamp and with mountain temps rising into the mid 30s at 8500' will conspire to dampen the snow surfaces on the steep sunlit slopes. With prolonged dampening, both natural and especially human triggered wet avalanches will be likely with daytime warming. Please choose terrain to avoid the steep sun-drenched slopes by midday - particularly those above roads and infrastructure. The danger may rise toward Considerable with extended warming....