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Avalanche Forecast

Archived

Feb 8th, 2022–Feb 9th, 2022

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

Regions

North Rockies.

Warm temperatures, rain below treeline and snow up high with strong to extreme wind will increase the likelihood of triggering the buried weak layer where it is present, destabilize the snowpack below treeline and build fresh wind slabs at higher elevations.

Confidence

High - We are confident the likelihood of avalanche will increase with the arrival of the forecast weather.

Weather Forecast

TUESDAY NIGHT: Cloudy with snowfall, 5 to 15 cm new snow and rain at lower elevations, strong southwest wind, alpine temperature -1 C, freezing level 1700 m.

WEDNESDAY: Cloudy with snowfall, 5 to 10 cm new snow with the higher amounts in the southwest of the region, rain at lower elevations, strong to extreme southwest wind, alpine temperature +2 C, freezing level rising to 2200 m.

THURSDAY: Mix of sun and cloud, 5 to 10 cm new snow with the higher amounts in the west of the region, strong to extreme west wind, alpine temperature -4 C, freezing level dropping to 1400 m.  

FRIDAY: Mostly sunny, moderate westerly wind, alpine temperature -4 C, freezing level 1300 m.

Avalanche Summary

On Monday, a small skier triggered wind slab avalanche was reported and several smaller slab avalanches released naturally on the buried weak layer. Wet loose avalanches were observed below 1000 m. 

On Sunday, a deep persistent slab avalanche was likely triggered naturally by intense warming and sun and released on depth hoar or the November crust. It occurred just south of the region (see this MIN report). Explosives triggered several large wind slab avalanches up to size 3.

On Saturday, several storm and wind slab avalanches up to size 2 were observed at treeline and in the alpine. Most of these avalanches released naturally, and two were likely triggered by riders.

Snowpack Summary

The recent storm brought 10 to 20 cm new snow and rain below 1000 m. The new snow formed storm slabs in sheltered areas and wind slabs in lee terrain features from strong south and west wind. This new snow added to the previous storm which brought 40 to 60 cm for much of the region, with the most in the southwest of the region and the least to the east of the divide and in the north. 

The snow will be particularly touchy where it sits on a weak layer of surface hoar crystals. Reports suggest that the surface hoar is likely most prominent in sheltered openings at and below treeline but could extend into wind-sheltered terrain in the alpine. Example terrain features to treat as suspect include the lee side of protected ridges, openings in the trees, cut blocks, and burns.

The lower snowpack is generally strong and well-bonded. The base of the snowpack is expected to be weak and faceted in shallow, rocky slopes east of the divide.

Terrain and Travel

  • Uncertainty is best managed through conservative terrain choices at this time.
  • Potential for wide propagation exists, fresh slabs may rest on surface hoar, facets and/or crust.
  • Watch for signs of instability like whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Rain or periods of intense solar radiation can rapidly enhance the effects of warming.

Problems

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.

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.

Loose Wet

Loose Wet avalanches are the release of wet unconsolidated snow or slush. These avalanches typically occur within layers of wet snow near the surface of the snowpack, but they may quickly gouge into lower snowpack layers. Like Loose Dry Avalanches, they start at a point and entrain snow as they move downhill, forming a fan-shaped avalanche. Other names for loose-wet avalanches include point-release avalanches or sluffs. Loose Wet avalanches can trigger slab avalanches that break into deeper snow layers.