Avalanche Forecast

Local enhancements in snowfall amounts possible near McBride.

WEDNESDAY NIGHT: Increasing cloud with flurries bringing up to 5 cm in most areas, strong southwest wind, freezing level valley bottom.

THURSDAY: 5-10 cm new snow in most areas, strong southwest ridgetop wind, freezing level 1100 m.

FRIDAY: 5-10 cm new snow, moderate westerly ridgetop wind, freezing level valley bottom.

SATURDAY: Up to 5 cm new snow, light to moderate southwest ridgetop wind, freezing level 800 m.

Observations from McBride and Valemount areas show evidence of a widespread natural avalanche cycle that took place during the previous storm. Several natural and machine triggered storm slabs size 2-3.5 (!) were reported on Tuesday near Valemount at alpine and treeline elevations. At least one of the very large machine triggered avalanches was initiated from a wind loaded start zone at the top of a large alpine feature, propagated for hundreds of meters along a ridge and ran to valley bottom. Thankfully the rider was able to escape unharmed.

Recent reports have been of excellent riding quality in the 40-80 cm of recent snow. Thick, reactive wind deposits up to 100 cm deep exist in lee features at upper elevations. The recent snow sits on old, facetted and/or extensively wind affected snow that sat on the surface during the extended cold, windy drought period. Some very large avalanches since the end of the storm have shown incredible propagation of hundreds of meters in alpine and treeline features, indicating that this layer is weak and may persist for some time. On the other hand, this MIN from Clemina describes very limited reactivity at this interface below treeline.

We've now got 80-180 cm of snow above the early February persistent weak layer which is composed of surface hoar. This layer is most prevalent at treeline and in "treeline-like" features like cutblocks. On steep south-facing terrain, this layer may consist of facets on a sun crust. We are awaiting reports of avalanche activity during the storm, specifically whether they indicate step- downs to this layer, to determine whether or not it continues to be a problem.

• Fresh snow rests on a problematic persistent slab, don't let good riding lure you into complacency.
• Be aware of the potential for large avalanches due to the presence of a persistent slab.
• Keep in mind that human triggering potential persists as natural avalanching tapers off.
• Uncertainty is best managed through conservative terrain choices at this time.
• Be especially cautious as you transition into wind affected terrain.