Signs of instability like pinwheeling and tree bombs will clue you into surface layers becoming unstable as temperatures rise on Wednesday.
The first sign of instability at one of our deeply buried weak layers could be a large, destructive avalanche. Choose terrain that won't expose you to the consequences.
Shifting winds have been acting on 10 to 15 cm of loose snow sitting on a freezing rain or rime crust, likely forming small wind slabs on a wide range of aspects in exposed areas. Southwest winds has and will continue to be the primary factor here.
A persistent weak layer of surface hoar is buried 50 to 70 cm down. This depth is prime for human triggering. Below treeline this layer may present as a rain crust.
Deeper in the snowpack, near the ground, the snowpack is very weak and can be triggered under the right circumstances. Be especially suspicious of shallow, rocky, or cross-loaded areas with variable snow depths.
Sunshine and warming on Wednesday will destabilize the surface on steep, sun exposed slopes. Wet loose avalanches in motion have potential to trigger weak layers deeper in the snowpack to create larger, more destructive avalanches.
No new avalanches were reported in the region on Monday.
Sunday's avalanche activity in the region consisted mainly of small (size 1 or less) dry loose releases from steeper terrain with skier traffic and ski cutting.
Although persistent and deep persistent avalanches have been on an encouraging decline in the region, forecast warming through Thursday brings real concern for the potential for natural as well as human triggering deep weak layers in the snowpack.
Generally up to about 10 cm but locally up to 20 cm of new snow has buried a new weak layer. It consists of faceted snow as well as surface hoar that has been observed at anywhere from 3 -10 mm in size in sheltered areas up to about 2200 m. On steep solar aspects this interface likely presents as a crust. At higher elevations the new snow has been getting blown around by variable winds and forming wind slabs on a range of aspects as a result.
A freezing rain or rime crust buried on January 18 now sits about 15-30 cm deep.
Additional, locally variable layers of crust, surface hoar, and facets may also be found in the top 30 to 50 cm of the snowpack. These layers have not yet produced widespread avalanches but are being tracked by professionals in the region along with the layers below, which are a more widespread concern.
Layers that are presently a concern include a surface hoar layer developed in early January, down roughy 50-70 cm and a melt-freeze crust from late December that is now down approximately 70-90 cm. These layers are responsible for our persistent slab problem.
Our deep persistent slab problem stems from a weak layer created in mid-November and it is now buried 100 to 190 cm deep. These layers are a major concern and can produce large or even very large avalanches with human or machine triggers.
Tuesday night
Cloud increasing throughout night, small amount of precipitation in western part of region, winds light to moderate from the Northwest, treeline temps around -6 C.
Wednesday
Mainly sunny. Winds moderate from the Northwest, treeline temps around 0 C. Likely above freezing layer from 1500-2000 m, particularly in the western part of the region.
Thursday
A mix of sun and cloud, nil precipitation, winds moderate from the Northwest, treeline temps around +2 C. Likely above freezing layer from 1500-2000 m, particularly in the western part of the region.
Friday
A mix of sun and cloud, trace precipitation, winds moderate from the Northwest, treeline temps around 0 C.
More details can be found in the Mountain Weather Forecast.
