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Avalanche Forecast

Archived

Feb 23rd, 2022–Feb 24th, 2022

Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.
Alpine
Natural avalanches unlikely, human triggered possible.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

South Coast Inland.

In the south of the region, a widespread storm slab may be reactive to human-triggering, especially in wind loaded terrain. The storm snow may be poorly bonded to the underlying crust.

In the north, recently formed wind slabs are expected to remain reactive.

Confidence

Low - Uncertainty is due to the limited number of field observations. Uncertainty is due to the speed, direction, or duration of the wind and its effect on the snowpack.

Weather Forecast

High pressure remains the dominant weather feature for the rest of the week. The next storm system is currently forecast to arrive on Saturday afternoon or evening. 

Wednesday Night: Mainly cloudy with light flurries, light to moderate NW wind, treeline low around -14 °C.

Thursday: Mainly sunny, light N wind, treeline high around -5 °C.

Friday: Sunny, light SW wind, treeline high around -3 °C.

Saturday: Increasing cloud cover with light snow beginning in the evening, moderate to strong SW wind, treeline high around -2 °C.

Avalanche Summary

On Tuesday, a natural size 2 cornice release was observed in the north of the region which did not pull a slab on the slope below. This MIN report describes three size 1.5-2 slab avalanches in the Coquihalla which are expected to have occurred on Monday. 

On Monday, several natural wind slabs were observed. In the north, these were limited to size 1. In the south, they were a bit bigger at size 1.5. Loose dry avalanches up to size 1.5 were also observed in the south of the region. 

On Sunday in the Coquihalla, a skier-triggered storm slab was reported on a SE aspect at treeline which had a slab depth varying between 20 and 55 cm. The MIN report includes a great photo showing the type of avalanches we continue to expect in the south of the region where the recent wind has loaded leeward terrain features. A natural size 2 storm slab was also reported on a SW aspect at 1850 m as well as a variety of small natural and human-triggered loose dry avalanches from steep slopes. 

On Sunday in the north of the region, a very small persistent slab avalanche was reported as part of a larger snowpack settlement which occurred at valley bottom near a creek. This failed on the late-January surface hoar down around 40 cm. This suggests that in the isolated areas where large surface hoar is still preserved, the interface may still capable of producing avalanches. 

Snowpack Summary

Weekend storm totals were highly variable across the region with around 5-10 cm in the north and around 30-50 cm around the Coquihalla and Allison Pass. Recently northerly winds have redistributed this snow in exposed terrain and formed reactive wind slabs. 

A weak crust layer from mid-February is now down around 20 cm in the north and as deep as 70 cm in the south. The melt-freeze crust is reported to exist on all aspects and elevations, except for high elevation northerly aspects in the north of the region. Facets and surface hoar can be found above the crust in the north of the region. 

A weak crust/facet/surface hoar interface from late-January is buried down 40-100cm. This layer was most reactive between 1700 m and 2000 m in the north of the region. While this layer now appears to be dormant through most of the region, it may still be possible to trigger it at upper treeline or lower alpine features on northerly aspects in the north of the region with a large load like a cornice or in shallow snowpack areas.

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Closely monitor how the new snow is bonding to the crust.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

Problems

Storm Slabs

Storm Slab avalanches are the release of a cohesive layer (a slab) of new snow that breaks within new snow or on the old snow surface. Storm-slabs typically last between a few hours and few days (following snowfall). Storm-slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.