Avalanche Forecast
Issued: Jan 30th, 2021 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Storm Slabs and Persistent Slabs.
shorton,
Avalanche Canada
Heavy snowfall is adding to an already weak snowpack and creating very dangerous avalanche conditions. Travel in avalanche terrain is not recommended.
Summary
Confidence
Weather Forecast
A frontal system will bring more snow and wind on Sunday.
SATURDAY NIGHT: Scattered flurries with 5-15 cm of snow, strong southeast wind, freezing level climbs to 1200 m with treeline temperatures around 0 C.
SUNDAY: Cloudy with continuing snowfall bringing 15-25 cm of new snow and 2-day snow totals to 40-60 cm. Snowfall eases overnight. Moderate to strong southeast winds. Freezing level around 1000 m with treeline temperatures around -1 C.
MONDAY: Cloudy with isolated flurries and a trace of new snow, light wind, freezing level drops to 900 m with treeline temperatures around -2 C.
TUESDAY: Scattered flurries with 15-25 cm of snow, moderate southwest wind, freezing level around 600 m with treeline temperatures around -3 C.
Avalanche Summary
Heavy snowfall over the weekend will likely result in natural avalanches and make human triggered avalanches very likely.
It has been a busy week for avalanche activity in the North Shore mountains, with human triggered avalanches reported everyday since Monday. These avalanches have failed on a prominent weak layer that was 30-60 cm deep at the time, and will be 60-100 cm deep by Sunday. Recent MIN reports show good examples of these avalanches (e.g. here, here, and here). North Shore Rescue responded to a serious, but non-fatal avalanche incident on Tuesday evening on Cypress Mountain. One person was involved and was partially buried. The avalanche was a size 2 storm slab on a west aspect at approximately 1100 m and failed on the recently buried weak layer.
While we are confident the new storm slabs will be very reactive on Sunday, we have some uncertainties about the likelihood of avalanches on the buried weak layer (which would be large if triggered).
Snowpack Summary
Weekend snowfall totals should reach 40-60 cm by Sunday afternoon, with deeper deposits on wind loaded slopes. This adds to snow from a midweek storm siting on a widespread crust, which could be 60-100 cm deep by Sunday. This crust also has weak facets and surface hoar on top of it in many areas. This widespread weak layer will probably take more time to gain strength than what is considered typical for the South Coast region. Click here to watch North Shore Rescue's January 29 snowpack discussion, which illustrates this concerning snowpack structure.
Terrain and Travel
- Avoid all avalanche terrain during periods of heavy snowfall.
- Only the most simple non-avalanche terrain free of overhead hazard is appropriate at this time.
- Be aware of the potential for large avalanches due to the presence of buried weak layers.
Problems
Storm Slabs
By Sunday afternoon there will likely be 40-60 cm of fresh snow from the weekend's storm, resulting in thick and touchy storm slabs. Expect natural avalanches in steep terrain during periods of heavy loading, while human triggered avalanches will be likely throughout the day.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Persistent Slabs
New snow is stressing a widespread weak layer consisting of a crust, with facets and/or surface hoar on top of it. This layer is roughly 60-100 cm deep and is expected to produce large avalanches for longer than what is typical after a storm on the South Coast.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Jan 31st, 2021 4:00PM
