Avalanche Forecast
Issued: Feb 26th, 2022 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Wind Slabs and Persistent Slabs.
jleblanc,
Avalanche Canada
Reactive wind slabs will likely form throughout Sunday. Diligently watch for changing conditions and rising hazard as the day progress.
Summary
Confidence
High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.
Weather Forecast
A shift in the weather pattern is expected from Saturday on. Continued snowfalls, rising temperatures, and back-to-normal winds are expected up to Tuesday.Â
Saturday night: Cloudy with flurries up to 5 cm. Freezing level returning to valley bottom. Alpine temperatures around -8C. Strong southerly winds up to 60 km/h.
Sunday: Snow 5-10 cm. Freezing level rising to 1400 m. Alpine temperatures around -6 C. Strong southerly winds up to 60 km/h.
Monday: Snow 10-15 cm. Freezing level rising to 1400 m. Alpine temperatures around -4 C. Moderate southerly winds gusting 50 km/h.
Tuesday: Snow 5-10 cm. Freezing level rising to 1600 m. Alpine temperatures around -2 C. Moderate southerly winds gusting 50 km/h.
Avalanche Summary
Friday, two massive natural cornice falls were observed in the region. One of them triggered a very large (size 3) persistent slab avalanche just outside Valemount on a south-facing alpine slope. The other cornice fall had debris the size of a very large truck. This evidence is showing that a large amount of snow is still easily being transported. It also highlights the fact that persistent slabs remain a concern in this region, although a large load is required to trigger an avalanche.Â
Snowpack Summary
Last week's extensive northerly winds have created heavily wind-affected surfaces in exposed areas and wind slabs in lee areas. Continued cold temperatures have transformed surface conditions since the latest snow (20-100 cm), about a week ago. A thin sun crust was observed on steep south-facing slopes at lower elevations. Large feathery surface hoar crystals have also been observed in sheltered areas on all elevations. Below ~1200 m, 15-25 cm of snow is now overlying a thick melt-freeze crust.Â
Up to 120 cm now overlies a weak layer formed in mid-February. This layer is comprised of surface hoar in sheltered areas, a melt-freeze crust at lower elevations, a sun-crust on steep solar aspects, and hard wind-affected snow in the alpine and exposed treeline. The late-January surface hoar/crust layer is now down 50-150 cm in the snowpack. During the last week, there was isolated reactivity on these layers. We will keep monitoring their reactivity as the next series of snowfalls will affect the region.
Terrain and Travel
- Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
- Wind slabs are most reactive during their formation.
- Closely monitor how the new snow is bonding to the old surface.
- If triggered, wind slabs avalanches may step down to deeper layers resulting in larger avalanches.
Problems
Wind Slabs
Strong winds and expected snowfalls (up to 15 cm) will likely reload previously scoured slopes and build fresh and reactive wind slabs on any exposed terrain, lee features, and around ridgelines. Uncertainty remains in how well the developing slabs will bond to underlying varied snow surfaces.
Aspects: North, North East, East, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Persistent Slabs
There are two prominent weak layers in the upper meter of the snowpack.
An upper layer exists down ~50-100 cm and is comprised of surface hoar in sheltered areas, a crust at lower elevations and on solar aspects, and hard wind-affected snow in the alpine and exposed treeline. Be particularly cautious in sheltered areas where surface hoar may be preserved, or south-facing aspects where past wind-loading had occurred and a sun crust may be buried.
The lower layer may be found 100-150 cm deep in the snowpack. This layer consists of faceted snow, a sun crust on steep solar aspect, and most notably large surface hoar crystals in sheltered terrain. This layer 'woke up' in the neighboring regions during the last storm and should be treated with caution with this incoming one. The most reactivity on this layer has been seen between 1600-2200 m in open areas in the trees, in cut blocks, and on steep convexities. Terrain features to be suspect of include the lee side of ridges, openings in trees, cut blocks, and burns, especially on northerly aspects where the layer may not be capped by a firm crust.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: Feb 27th, 2022 4:00PM
