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Avalanche Forecast

Archived

Jan 7th, 2022–Jan 8th, 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 avalanches possible, human triggered probable.
Treeline
Natural avalanches unlikely, human triggered possible.
Below Treeline
Natural avalanches unlikely, human triggered possible.

Regions

Lizard-Flathead.

Storm stabs may continue to be reactive to skiers. The most reactive deposits will be around steep and convex features in open terrain, or anywhere wind encourages slabs to form.

Confidence

Moderate - Uncertainty is due to how the snowpack will react to the forecast weather. Uncertainty is due to how buried persistent weak layers will react with the forecast incoming weather.

Weather Forecast

Friday night: Snowfall tapering overnight, 5-10 cm with the far south of the region possibly accumulating upwards of 20 cm overnight. Strong SW wind. Treeline high around -16 °C.

Saturday: Mostly cloudy with isolated flurries, up to 5 cm. Moderate SW wind. Treeline high around -8 °C.

Sunday: A mix of sun and cloud. Moderate W wind. Increasing temperatures with a treeline high around -4 °C.

Monday: Cloudy with sunny breaks. Moderate SW wind. Treeline high around -4 °C.

Avalanche Summary

On Friday, explosives triggered storm slabs to size 2.5, and skiers triggered avalanches to size 2.

Evidence of a natural storm slab avalanche cycle size 2-2.5 was observed on NE aspects Wednesday and Thursday, likely having run during the storm earlier in the week. 

On Monday and Tuesday, storm slabs were reactive to explosive up to size 2 and ski cuts produced storm slabs and loose dry avalanches up to size 1. By Wednesday, explosive results were limited to size 1 loose dry.

On Sunday, a size 2.5 persistent slab avalanche was triggered on an E aspect at treeline. This avalanche is detailed in a MIN post and features in our latest blog post, Photos of recent persistent slab avalanches in the southern interior.

Snowpack Summary

Upwards of 40 cm new snow accumulated by the end of Friday with warming temperatures. In open terrain and upper elevations, wind developed more reactive deposits formed around lee and convex features.

An accumulated total of 40-70 cm of new and recent snow now sits over variable and potentially weak snow surfaces including widespread facets, wind affected snow, and/or surface hoar in sheltered areas, which may make for a weak bond at this interface.

The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 90-200 cm. Activity on this layer has been sporadic, the most recent persistent slab avalanche in the region was on January 2. This layer has created a low likelihood, high consequence scenario which is best managed through conservative terrain choices and disciplined backcountry travel techniques.

Terrain and Travel

  • Seek out sheltered terrain where new snow hasn't been wind-affected.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.
  • Avoid shallow, rocky areas where the snowpack transitions from thick to thin.

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.