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Avalanche Forecast

Archived

Jan 15th, 2020–Jan 17th, 2020

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

Regions

North Rockies.

Wind slabs may remain sensitive to human triggering, especially in steep features near ridge crest. Although unlikely, buried Surface Hoar could produce very large destructive avalanches. This weak layer is most prevalent in the south, especially in the Torpy/McGregor zone.

Confidence

Low - Uncertainty is due to the extreme variability of wind effect on the snowpack. Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast.

Weather Forecast

It should warm up *slightly* this weekend but the forecast is largely made up of colder than average temperatures, mainly cloudy skies and a few dribbs/drabbs of snow.

WEDNESDAY NIGHT: Alpine temperature -36° C, strong east/southeast wind, trace of snow possible.

THURSDAY: Broken cloud cover, alpine temperature -30° C, strong east/southeast wind, most of the region should only get a trace of snow but the Torpy and western side of the Kakwa could see as much as 15 cm of snow with the Renshaw picking up 5 to 10 cm of new snow.

FRIDAY: Broken cloud cover at dawn clearing throughout the day, alpine temperature rising to -17° C, light variable wind at most elevations with moderate southwest wind at ridgetop, no significant precipitation expected.

SATURDAY: A few clouds at dawn building to broken cloud cover by sunset, alpine temperature rising to -10° C, moderate to strong wind generally out of the south, trace of snow possible.

Avalanche Summary

Control work on Tuesday produced one size 2 avalanche on a southwest facing feature around 1400 m in the Pine Pass zone. 

Also on Tuesday, a natural size 2 persistent slab avalanche was observed on a south facing slope around 1750 m in the mountains near Crescent Spur, this avalanche is suspected to have failed on the late December Surface Hoar. 

Ongoing cold temperatures are likely tempering avalanche activity.

The latest report of avalanche activity on the surface hoar layer described in the snowpack summary was from January 9. It occurred near the McGregors on a southerly aspect at 1500 m, there's also a great visual of this kind of activity from January 10th in the Torpy on the PGBCSki FB page.

Snowpack Summary

Around 20 to 50 cm of storm snow has accumulated since late last week. This has created soft surface conditions in sheltered terrain but strong wind has redistributed the snow in exposed terrain, forming wind slabs. The wind changed directions from southwest to northeast over the weekend, meaning that wind-affected snow and wind slabs may be found on all aspects at and above treeline. 

A weak layer of feathery surface hoar buried in late December remains a concern. The layer has been found across much of the North Rockies region, but it has only become a problem in particular areas, such as around McBride and the McGregors/Torpy. It seems to be most prevalent in sheltered treeline features 50 to 150 cm below the surface.

Terrain and Travel

  • Recent wind has varied in direction so watch for wind slabs on all aspects.
  • Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
  • Back off if you encounter whumpfing, hollow sounds, or shooting cracks.
  • Avoid convexities as well as steep, open and/or sparsely treed slopes at and below treeline.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind 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.