Avalanche Forecast

A short burst of southeast wind on Monday

Sunday night: Cloudy, 5-10 cm of snow above 400 m, winds shifting to southeast and increasing to moderate, treeline temperatures near -8 C. 

Monday: Cloudy, 5-10 cm of snow above 500 m, moderate southeast winds easing to light, treeline temperatures near -7 C.

Tuesday: Mainly cloudy, light southwest winds, treeline temperatures near -9 C, freezing level near valley bottom.

Wednesday: Cloudy, 5-10 cm of snow over 300 m, moderate southeast winds, treeline temperatures near -4 C.

On Sunday, operators reported numerous small to large (size 1.5-3) human and explosive-triggered avalanches releasing within in the storm snow on a variety of aspects. 

We also received reports of four large (size 2-2.5) explosive-triggered persistent slab avalanches failing on the early December crust/facet layer. These occurred on northwest and northeast aspects around 2000 m. A large (size 2.5) explosive-triggered cornice fall was also reported. 

A natural avalanche cycle occurred early Saturday morning that produced several large (up to size 2.5) avalanches releasing in the storm snow. Operators just east of the region reported one very large (size 3-3.5) avalanche. Below treeline, operators reported several natural small (size 1) avalanches out of steep rocky terrain. Riders near Brohm Ridge shared photos in this MIN report of touchy conditions below treeline on Saturday morning.

Bands of localized precipitation are forecast to bring another 10-20 cm of snow to the mountains by late Monday. A shift in wind direction from the southwest to southeast may form fresh wind slabs in a tricky cross-loading pattern at upper elevations. It may be possible to trigger wind slabs in lee terrain features, such as down-wind of ridges and roll-overs. Pay attention to conditions that change with exposure to wind and monitor for cracking or drum-like sounds.

An impressive storm over the weekend brought 40-70 cm of new snow to the mountains with strong southwest winds. Below the storm snow (down 60-100 cm), there is a layer of weak facets (sugary snow) above a crust that formed in early December. Over the weekend, snowpack tests at upper treeline elevations produced sudden results at this interface (see this, this, and this MIN report). On Sunday, operators reported large, explosive-triggered avalanches releasing on this layer in alpine start zones. This persistent slab problem warrants careful evaluation and conservative route-finding as the recent snow consolidates into a more cohesive slab over the weak layer.

With this storm event, a greater number of areas below treeline are meeting the threshold snow depth for avalanches. 

• 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 a persistent slab.
• Cornice failures could trigger very large and destructive avalanches.
• Uncertainty is best managed through conservative terrain choices at this time.
• Choose low-angled, sheltered terrain where new snow hasn't been wind-affected.