Lizard-Flathead

Wind slabs are expected to remain reactive in exposed high elevation terrain on Tuesday. It may still be possible to trigger a buried weak layer in isolated areas but the likelihood is decreasing with the cooler weather. 

Dry and mainly sunny conditions are expected for the week except for a weak disturbance Tuesday night which may bring light flurries. A major warming event is current forecast to arrive late Wednesday which may persist for several days. 

Monday Night: Light flurries in the evening then clearing, light to moderate SW wind, freezing level dropping to valley bottom.

Tuesday: A mix of sun and cloud with a chance of flurries overnight, moderate SW wind, freezing levels reaching around 1500 m.

Wednesday: A mix of sun and cloud, moderate NW wind, freezing levels climbing to around 2000 m.

Thursday: Mainly sunny, moderate SW wind, freezing levels reaching near 2500 m with an inversion.

An early report from Monday includes explosives triggering numerous of cornices, with some subsequently triggering slabs on the slope below. 

On Sunday, a ski cut triggered a size 1.5 wind slab at 1950 m on a north aspect which was 15-25 cm thick and a skier accidently triggered a size 2 wind slab which failed down 30-60 cm on the mid-January crust. An explosive-triggered size 2.5 wind slab was also reported which failed on the mid-January crust down 30 cm and then stepped down to an older layer 100 cm deep in the snowpack. 

This MIN report summarizes the recent conditions well and describes natural and human-triggered slab avalanches size 1-2 as well as whumphing and shooting cracks. 

On Saturday, a natural cornice fall triggered a size 2 storm slab which failed down 30 cm and then stepped down to deeper layers in the snowpack. Several natural wind slabs size 1.5-2.5 were also reported in alpine terrain on NW-NE aspects. A small cornice failure was also reported which did not trigger a slab. 

A new melt-freeze crust is expected on solar aspects into the alpine and on all aspects at lower elevations. Ongoing periods of strong wind from the southwest through northwest have formed reactive wind slabs and large cornices in exposed terrain at higher elevations. 

The January 30 interface is now typically down 20-40 cm and consists of a melt-freeze crust at lower elevations and on solar aspects extending into the alpine, spotty surface hoar in sheltered areas at and below treeline, and small facets in some areas. 

The widespread January 18 rain crust is now around 50-70 cm deep with weak faceted snow above. This layer appears to have woken up with the weekend warming and at least three avalanches likely involved this layer.

The early December crust/facet persistent weak layer is now 100-200 cm deep. This layer produced numerous large avalanches in January but is now considered dormant. See this forecaster blog on how to manage this layer as it may come into play again later this season. 

• Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
• Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
• Look for signs of instability: whumphing, hollow sounds, shooting cracks, and recent avalanches.
• Cornices become weak with daytime heating or solar exposure.