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Avalanche Forecast

Archived

Nov 25th, 2021–Nov 26th, 2021

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

Regions

Purcells.

Keep your head up as you gain elevation and exposure to the wind. Forecast snowfall amounts vary through the region, expect slabs to be more reactive as snow stacks up.

Confidence

Low - Uncertainty is due to the limited number of field observations. Forecast precipitation (either snow or rain) amounts are uncertain.

Weather Forecast

Thursday night: Flurries and snow, 5-30 cm. Southwest winds, 35-45 km/hr. Alpine temperature low -6C. Freezing level 1000 m.

As this system tracks through the Purcells forecast snowfall amounts fall quickly west to east. The western peaks and areas around the Bugaboos may accumulate over 30 cm overnight and into Friday with significantly less reaching the Rocky Mountain Trench.

Friday: Snow and flurries, 5-20 cm. Southwest winds, 45-50 km/hr. Alpine temperature high -3C. Freezing level 1400m.

Saturday: Mostly cloudy with sunny breaks. Southwest winds 15-30 km/hr. Alpine temperature high -1C. Freezing level 1400 m and rising.

Sunday: Wet Flurries and snow, 10-25 cm. Southwest winds 45-60 km/hr. Alpine temperature high 1C. Freezing level 2100 m. 

Avalanche Summary

On Tuesday, November 23, explosives triggered a large (size 2) avalanche which failed on facets at the bottom of the snowpack. This was a reloaded slope (already avalanched this season) and occurred on a north aspect at 2270 m.

On Monday, November 22, explosives triggered a few small (size 1) wind slab avalanches in immediate lee features. 

Snowpack Summary

10-25 cm of recent snow is being transported by wind and developing slabs in lee features. The mid-November rain crust is down 30-50 cm, and has been reported up 2100 m.

A couple of crusts are found in the lower snowpack: A thin rain crust from early November is found 40 cm above the ground in deeper snowpacks and at the ground in shallower areas, it likely does not exist above 2300 m. A melt-freeze crust and facets from October is at the base of the snowpack, and possibly only exists above 1900 m.

Snowpack depths range from 50-140 cm at treeline elevations, and exceed 200 cm in the high alpine. Deeper snowpacks are found around the Bugaboos and northern parts of the forecast region. Snowpack depths decrease rapidly below 1700 m.

Early season hazards are very real right now, be wary of thin/shallow snowpacks, rocks, stumps, creeks, and other sharks hidden under a dusting of snow.

Terrain and Travel

  • Be alert to conditions that change with elevation and wind exposure.
  • Avoid areas where the snow feels stiff and/or slabby.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Use caution on large alpine slopes, especially around thin areas that may propagate to deeper instabilities.

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.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.