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Avalanche Forecast

Archived

Feb 28th, 2020–Mar 2nd, 2020

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

Regions

North Rockies.

For all the region except the north, a strong storm on Friday night will build slabs that will likely be reactive this weekend, requiring terrain avoidance and a conservative mindset to travel safely. For the north, treat the danger as CONSIDERABLE with less snow but windy.

Confidence

Moderate - Forecast snowfall amounts are uncertain.

Weather Forecast

FRIDAY NIGHT: Cloudy with snowfall, accumulation 15 to 25 cm for most of the region and 5 cm in the north around Pine Pass, moderate south switching to northeast wind, alpine temperature -8 C.

SATURDAY: Cloudy with snowfall and afternoon clearing, accumulation 5 to 10 cm for most of the region and trace around Pine Pass, moderate northeast wind, alpine temperature -10 C.

SUNDAY: Mix of sun and cloud, moderate increase to strong southwest wind, alpine temperature -10 C.

MONDAY: Cloudy with snowfall and afternoon clearing, accumulation 5 to 15 cm, strong decreasing to moderate northwest wind, alpine temperature -8 C, freezing level rising to 1000 m.

Avalanche Summary

Within the past few days a few small (size 1) to large (size 2 to 3) wind and storm slab avalanches were reported in the area. They generally occurred within the upper 20 to 50 cm of snow, on north to east aspects, and at treeline and alpine elevations. Some of them may have slid on the melt-freeze crust described in the Snowpack Summary. A few loose avalanches were also noted and they were generally small.

Avalanche activity is expected to increase this weekend due to the stormy conditions that will bring more snow and wind to the region.

Snowpack Summary

A storm on Friday night for most of the region (except around Pine Pass and north) will drop around 20 to 30 cm of snow by Saturday afternoon. This will overly previously wind-affected snow in exposed terrain and otherwise around 20 to 50 cm of soft snow in sheltered terrain. The new snow will fall with south switching to northeast wind, so slabs are expected to be found on all aspects and at all elevations. There are also a couple buried melt-freeze crusts in the snowpack and all this snow may not be bonding well to them. Cornices have been reported as growing large and fragile.

The lower snowpack is strong in many parts of the region with two main exceptions:

  • A weak layer of surface hoar buried 50 to 100 cm has been a problem around treeline elevations at Pine Pass. The layer has also been observed in other parts of the region, such as Torpy, but seems to be less of a problem further south towards McBride. Although unlikely to trigger, an avalanche on this layer would be large.
  • Steep slopes where the snowpack is shallow and rocky could harbour weak basal facets.

Terrain and Travel

  • Dial back your terrain choices if you are seeing more than 20 cm of new snow.
  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Make conservative terrain choices and avoid overhead hazard.
  • Be aware of the potential for large avalanches due to the presence of buried surface hoar.
  • Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.

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.