Avalanche Forecast

Sunday ushers in Dr. Jekyll's benign weather following Mr. Hyde's Saturday storm

Saturday night: Decreasing cloudiness, up to 5 cm of snow, moderate west winds decreasing to light, treeline temperatures cooling from -5 C to -9 C, freezing level dropping to valley bottom.

Sunday: Clearing in the afternoon, no new snow expected, winds becoming northeast and light, high treeline temperatures near -7 C, freezing level around 200 m.

Monday: Mainly sunny, no new snow expected, light northeast winds, high treeline temperatures near-7 C, freezing level at valley bottom.

Tuesday: Increasing cloudiness, no new snow expected, winds becoming southwest and increasing to moderate, high treeline temperatures near -5 C, freezing level at valley bottom.

On Saturday, operators reported numerous small to very large (size 1-3) avalanches releasing naturally in the storm snow across elevations and aspects. Although natural avalanche activity is tapering, avalanche conditions may remain primed for human-triggering on Sunday. Avalanches in the new snow have the potential to step-down to recently reactive weak layers, producing very large, destructive avalanches. Cornices may also reach their breaking point, triggering persistent slab avalanches on slopes below. 

On Thursday, we received reports of two large (size 2-3) avalanches that released on a persistent weak layer on northwest and southwest aspects between 1700-1900 m. There are valuable photos and accounts in this MIN report and this MIN report. Notably, skiers remote-triggered these avalanches while traveling uphill. Several small (size 1-1.5) sympathetic avalanches also released on nearby terrain features during these close calls. 

Saturday's powerful storm brought 40-70 cm of snow to the mountains. Gradual warming and extreme southwest winds likely accelerated and compounded slab formation. Storm slabs may be poorly bonded to previous snow surfaces, which include hard wind-scoured surfaces, cold light snow, and possible surface hoar in sheltered areas. Stay alert to changing slab conditions as you move into wind-exposed terrain, and monitor the bond of the new snow to the old snow surface. 

A culprit weak layer of facets (sugary snow) can be found down 120-190 cm deep over a widespread crust that formed in early December. There has been abundant evidence over the past week that this weak layer is reactive to human triggering and has the potential to propagate across terrain features. These conditions require wide, conservative terrain margins and disciplined backcountry travel techniques. Get more details and photos in our forecaster blog. 

• The trees are not a safe haven, travel at treeline requires expert knowledge and diligence.
• Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
• Remote triggering is a concern, avoid terrain where triggering slopes from below is possible
• Cornice failures could trigger very large and destructive avalanches.
• Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.