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Avalanche Forecast

Archived

Jan 11th, 2022–Jan 12th, 2022

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

Regions

Northwest Coastal.

A touchy storm slab with warming temperatures is creating tricky avalanche conditions and old weak layers deep in the snowpack have the potential to wake up this week. Use extra caution around steep south facing slopes in the afternoon if the sun is shining brightly. 

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather.

Weather Forecast

An offshore ridge of high pressure is expected to build on Wednesday bringing a break in the weather before the next storm system arrives on Thursday night. 

Tuesday Overnight: Snowfall at higher elevations 5-15 cm, moderate SW wind, treeline temperature around 0 °C, freezing level as high as 1000 m. 

Wednesday: Mainly cloudy with sunny breaks in the afternoon, moderate to light SW wind, treeline high around 0 °C, freezing level as high as 1100 m. 

Thursday: A mix of sun and cloud, light variable wind, treeline temperature around +2 °C, freezing level as high as 1500 m with a temperature inversion.  

Friday: Potential for heavy snowfall/rainfall, strong S wind, treeline temperature around +2 °C, freezing level as high as 1300 m. 

Avalanche Summary

Early reports from Tuesday suggest that the natural activity has tapered off but a few natural wind slabs were still observed in the north. Explosives were triggering numerous storm slab avalanches on Tuesday morning. At lower elevations, natural loose wet avalanches have started to be reported. 

On Sunday and Monday, a natural avalanche cycle occurred in the north of the region where 50-80+ cm of storm snow had accumulated. These were primarily storm slab avalanches up to size 4 which were most reactive in wind loaded terrain. In the south of the region, a variety of natural avalanche activity was reported but it doesn't seem to be as widespread as in the north and the avalanche size was generally smaller. 

On Monday in the far south of the region, explosives triggered a deep persistent avalanche which failed on basal facets near the ground. While this appears to be an isolated event so far, it could be an indicator that deeper weaknesses in the snowpack could be waking up with the warming temperatures. 

Snowpack Summary

40-80 cm of storm snow accumulated over the weekend, with the highest amounts along the immediate coastal areas and the north of the region. Recent strong SW winds have redistributed this new snow into wind slabs in exposed terrain. Below the recent storm snow is a highly variable snow surface which includes heavily wind-affected surfaces (scouring, old wind slabs, sastrugi, etc.) from last week's outflow winds, widespread faceting from the prolonged cold temperatures, and/or small surface hoar in sheltered terrain. This weak interface and a hard bed surface may increase the reactivity of the new storm slabs.

The early December rain crust is up to 10 cm thick, down 100-200 cm in the snowpack, and exists to an average of 1400 m in elevation. While this layer had generally gone dormant in the region through the cold period, it still has the possibility of waking up and will be tested this week with the forecast warming event and ongoing snow accumulation. Extra caution is necessary while the snowpack undergoes this substantial warming after the prolonged period of cold conditions. 

Terrain and Travel

  • Continue to make conservative terrain choices while the storm snow settles and stabilizes.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.
  • Extra caution for areas experiencing rapidly warming temperatures for the first time.
  • Avoid avalanche terrain during periods of strong sun.

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.

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.