Heightened avalanche conditions exist due to new snow and strong westerly winds. Wind slabs have formed on the lee sides of terrain features at upper elevations and will be sensitive to human triggering. In wind-sheltered areas above about 10,500 feet, human-triggered soft slab avalanches remain possible where new snow rests on collapsible crusts and older persistent weak layers. Avalanche likelihood decreases at lower elevations due to an old rain crust, but careful evaluation of avalanche terrain is still necessary in case instabilities are lingering within the new snow.
Strong westerly winds have formed thick wind slabs on the lee sides of terrain features. Where this avalanche problem overlays the persistent slab avalanche problem, a triggered wind slab could both propagate wider and become larger than expected. Wind slabs can be avoided by sticking to sheltered or wind-scoured areas.
An example of a wind slab located on the lee side of a ridgeline.
Soft slab avalanches will be possible to human trigger where recent snow has accumulated over collapsible crusts and older faceted weak layers. Underneath the recent storm snow, the old snowpack is highly variable due to record-warm temperatures in December and previous extreme wind events. So expect variable feedback, and don't expect the snowpack structure to remain the same from one part of a slope to another part of the slope. In some areas, this avalanche problem will feel unlikely to trigger, while right next door, an avalanche could propagate wider than expected.
One example of a collapsible crust over weak facets, now hidden under the recent storm snow. This combination could propagate an avalanche wider than expected.
24-hour snow totals as of 5am: Remote weather stations in the NW Mountain forecast are reporting .7 to 1.1 SWE, with snow totals close to a foot. In the SE Mountain forecast area, the Butte Snotel is reporting .3 SWE, with the CBMR pow cam showing about 7" of new snow. Snow showers were ongoing during the 5am hour, so hopefully those numbers grow this morning.
This winter has been plagued by drought conditions and well-above-average temperatures. Thick crusts have formed on southerly facing slopes, or those slopes were melted back to dry ground. Some of the most concerning weak layers now exist where crusts thin through aspect changes and overlay weak facets. Extreme wind events in December further created wildly varying snow surfaces. A rain event on Christmas further poured some salt in the wound and made a rain crust up to about 10,700ft. The current storm has now finally returned us to winter and created a new round of avalanche problems.
