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Avalanche Forecast

Archived

Mar 4th, 2017–Mar 5th, 2017

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

Regions

South Coast.

Two incidents Saturday remind us that a potentially dangerous storm/wind slab remains sensitive to human triggering. Caution and restraint is urged at this time. Take a conservative approach as you travel in the mountains Sunday.

Confidence

Moderate - Wind effect is extremely variable

Weather Forecast

An unsettled pattern opens the door to a string of relatively small low-pressure systems that should deliver modest snowfall to the region throughout the forecast period. Cold air currently in place will help to keep freezing levels low, at least through Tuesday. All bets are off Wednesday, when the weather models show an influx of moist warm air that will likely push the freezing level up towards 1800m and deliver 10 to 20mm of precipitation. SUNDAY: Overcast skies, freezing level near valley bottom rising to 500m in the afternoon, light SW wind, 1 to 5cm of snow. MONDAY: Overcast skies, freezing level around 500m, moderate SW wind, 1 to 5 cm of snow. TUESDAY: Overcast skies, freezing level rising to around 800m in the afternoon, strong SW wind, 10 to 20mm of precipitation expected. Visit avalanche.ca/weather for a more detailed mountain weather forecast.

Avalanche Summary

There were two significant avalanche accidents on the South Coast Saturday. Please recognize that at the time of writing, details are sparse, and in an evolving situation like this some information may prove to be incorrect. The first incident occurred west of Whistler in the Sea-to-Sky region. Initial details suggest the avalanche occurred on a west-facing feature. Size is estimated to be 2 to 2.5, approximately 80m in width with a 100cm crown. One critical burial was reported. The second incident occurred in the South Coast region where one person was reported to be fully buried in a feature called the Tony Baker Gully near Cypress Mountain. North Shore SAR has removed the person from the scene with reportedly serious injuries.These incidents serve as reminders that dangerous conditions still exist and caution is required when planning and carrying out trips in the region.

Snowpack Summary

Strong winds out of the south/southwest have taken the 30 to 100cm of recent storm snow and formed it into a reactive slab. Recent observations suggest this slab ranges from 20 to 100cm in depth throughout the region, but it could easily be twice that deep on lee features at and above treeline. Fluctuating temperatures have likely resulted in weaknesses within this recent storm snow too. This slab is currently bonding poorly to the old surface that includes a sun crust on southerly aspects, and surface hoar on shaded aspects. Below this interface is the mid-February crust which may remain active. This crust has been reported to have facets above it, and should be easy to find and test in your profiles.  The mid and lower snowpack appear to be well settled and strong.

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.