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Avalanche Forecast

Archived

Jan 17th, 2020–Jan 20th, 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 are widespread and may be found in areas you are not used to seeing them, seek out wind sheltered terrain this weekend to avoid wind slabs and find the best riding conditions. Steer clear of any glide cracks you come across, they've recently produced large avalanches.

Confidence

Low - Uncertainty is due to the extreme variability of wind effect on the snowpack. Uncertainty is due to the limited number of field observations.

Weather Forecast

Temperatures should begin to warm as southwest flow sets up this weekend, look for a few dribs and drabs of snow through the forecast period too.

FRIDAY NIGHT: Alpine temperature -18, light variable wind, no significant precipitation expected.

SATURDAY: Broken cloud cover, alpine temperature -8 C, light/moderate south wind, 5 to 10 cm of snow possible across the region.

SUNDAY: Broken cloud cover, alpine temperature -4 C, moderate south wind, 5 to 10 cm of snow possible across the region.

MONDAY: Broken cloud cover, alpine temperature -3 C, light/moderate south wind, trace of snow possible across the region.

Avalanche Summary

There have been a number of glide cracks that have failed naturally as very large avalanches in the Torpy area recently. Glide cracks are seemingly unpredictable and need to be given a wide berth. There are some great photos on the PGBCSki FB page.

A small wind slab was reported from west facing terrain at 2100 m Thursday. Wind slabs on west facing features are somewhat unusual but recent winds from a variety of directions have formed wind slabs in places we aren't used to seeing them.

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.

Snowpack Summary

20 to 50 cm of settled storm snow has been subject to winds from all directions. Wind slabs are likely to 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 areas of hard wind slab on alpine features.
  • Seek out wind sheltered terrain below treeline where you can avoid wind slabs and find great riding.
  • Be aware of the potential for large avalanches due to the presence of a persistent slab.

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.