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Avalanche Forecast

Archived

Jan 3rd, 2021–Jan 4th, 2021

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

Regions

Sea To Sky.

In the midst of an active weather pattern, snowfall amounts are uncertain on Monday. If it snows a lot, expect reactive storm slabs, choose simple terrain and avoid overhead hazard. If it snows a little, expect reactive storm slabs, choose simple terrain and avoid overhead hazard

Confidence

Moderate - Uncertainty is due to the timing, track, & intensity of the incoming weather system. Forecast snowfall amounts are uncertain.

Weather Forecast

Disagreement between weather models leaves us with a high degree of uncertainty around the tracking of the low pressure system, how much precipitation it will bring and where the bulk of it will fall on Monday.

Sunday night: Flurries, 5-10 cm, strong southwest wind, freezing level 800 m.

Monday: Snow, 5-20 cm, moderate southwest wind, alpine high -5, freezing level 1000 m.

Tuesday: Snow 10-15 cm, strong southerly wind, alpine high -5, freezing level 1000 m.

Wednesday: Snow 20-40 cm, strong southwest wind easing to moderate, alpine high -4, freezing level 1300 m.

Avalanche Summary

A large, natural storm slab avalanche cycle size 3-4 occurred near Pemberton over the weekend. Natural and explosive triggered storm slabs size 1-2 were reported elsewhere. This MIN report from Friday illustrates the active avalanche conditions during this storm.

Explosive triggered persistent slab avalanches size 2-2.5 were reported Sunday. Several large natural and human triggered persistent slab avalanches occurred early last week:

  • There was a fatal avalanche in the South Coast Inland region (near the Sea to Sky boundary) north of Pemberton in the Railroad Pass area last Monday that resulted in two fatalities. It was reported to be a size 2 persistent slab avalanche on a west aspect, around 1650 m. The RCMP press release can be viewed here, and the Avalanche Canada report can be found here.  
  • A size 2.5 avalanche was triggered on Monday by a skier on Rainbow Mountain, which resulted in a full burial and, thankfully, a successful rescue. The avalanche failed on a 60 cm deep crust and facet layer on a northeast aspect around 1800 m. 
  • A natural size 3 persistent slab avalanche was reported on Mount MacBeth on Monday, check out this MIN report for details of this observation.

These avalanches highlight the ongoing potential to trigger persistent weak layers in the snowpack. 

Snowpack Summary

10-30 cm of new snow between Sunday night and Monday afternoon and strong southwest wind, continue to build widespread storm slabs. Recent storm totals are well over 100 cm.

The snowpack is currently quite complex. The layer of greatest concern is a melt-freeze crust from early December, found around 100-200 cm deep in the snowpack. This crust may have surface hoar or sugary faceted grains sitting above it. There have been several recent large natural and human triggered avalanches on this layer and new snow loads as well as large loads from storm slab avalanches have potential to trigger these layers.

The remainder of the snowpack is well-settled.

Terrain and Travel

  • Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
  • Use conservative route selection. Choose simple, low-angle, well-supported terrain with no overhead hazard.
  • Storm slabs in motion may step down to deeper layers resulting in large avalanches.
  • Be aware of the potential for large avalanches due to the presence of buried persistent weak layers.

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.