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Avalanche Forecast

Archived

Feb 19th, 2022–Feb 20th, 2022

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

Regions

Purcells.

Keep terrain selection conservative as storm snow accumulates. 

Small avalanches may step down to deeper instabilities, most likely on sheltered north facing slopes.

Confidence

Moderate - Forecast snowfall amounts are uncertain. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

SATURDAY NIGHT: Light snowfall overnight, 5-10cm possible. Winds ease to light southwesterlies. Freezing levels drop below 1000 m. 

SUNDAY: Mostly cloudy with flurries bringing 5-10 cm of snow and light winds from the northwest. Freezing levels drop to valley bottom. Alpine high of -5.

MONDAY: Mix of sun and cloud, light winds from the northeast. Freezing levels at valley bottom with alpine highs of -10. Chance of flurries. 

TUESDAY: Mostly clear skies with moderate easterly winds. Freezing levels below valley bottom, with alpine highs of -20. 

Avalanche Summary

While no significant human triggered avalanches have been reported over the past week, the incoming storm will likely form reactive storm slabs as snow accumulates.

We have seen limited recent avalanche activity on the late January surface hoar layer, with the most recent report being a cornice triggered size 2.5 slab west of Forster Creek last Sunday (Feb 13). This avalanche occurred on north aspect at 2250 m. There is uncertainty about whether this problem will become more reactive with the incoming storm.

Snowpack Summary

New snow will form storm slabs at all elevations. The storm snow will bury a small surface hoar layer in sheltered terrain - which sits over a melt freeze crust on solar aspects at all elevations, and wind effected surfaces in exposed terrain. 

A layer of buried surface hoar sits 30-50cm deep in the upper snowpack, most likely to be found and triggered on north aspects in sheltered areas. This layer has produced variable results in recent snowpack tests, and may still be reactive on some steep convexities. 

The lower snowpack is well consolidated, with a crust/facet layer found 80 to 150 cm deep. It is currently considered dormant, but could become active later this season. Check out the forecaster blog for more information. 

Terrain and Travel

  • Watch for fresh storm slabs building throughout the day.
  • If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
  • Carefully assess open slopes and convex rolls where buried surface hoar may be preserved.

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.