Avalanche Forecast

Moderate - Uncertainty is due to the fact that persistent slabs are particularly difficult to forecast. Forecast precipitation (either snow or rain) amounts are uncertain.

Snowfall will continue into Monday. Tuesday evening marks a break in the storm, with a brief clearing proceeding the next system arriving Wednesday night.

Sunday Overnight: Continued snowfall, 20-50cm cm of accumulation expected, highest amount in the Squamish area. Freezing levels rising to around 800m, dropping to 300m by early morning. Strong to extreme southwest winds easing moderate to strong.

Monday: Another stormy day, 15-40 cm of new snow accumulation, heaviest accumulation around Squamish. Winds shifting to the south in the moderate to strong range. Freezing levels around 300m. Snowfall becoming lighter, another 5-15 cm expected overnight, freezing levels dropping to valley bottom, alpine temperatures dropping to around -12 C.

Tuesday: Lighter snowfall, 5-15 cm of accumulation. Light to moderate southerly winds, freezing levels at valley bottom. Possible clearing overnight, alpine temperatures dropping to -15 C.

Wednesday: A quieter day, cloud cover building into the afternoon as another system approaches from the pacific. Alpine temperatures around -13 C, rising into the afternoon. Light northwest winds at ridge-crest.

With heavy snowfall, high wind, and warming temperatures overnight we expect a widespread natural avalanche cycle occurred.

On Friday, professional operations reported natural and explosive triggered cornice failures up to size 2 that triggered small slab avalanches on the slopes below. 

We have been paying close attention to the early December crust, which has formed a persistent weak layer in the region. The last reported avalanche on this layer was on Dec 24, but it produced several notable avalanches around Dec 16 at elevations between 1800-2100 m. Learn more about how this persistent weak layer is developing in our latest forecaster blog.

Persistent cold temperatures in the last week may have made cornices facetted and weak, highlighting the importance of avoiding overhead hazard and giving them a wide berth when travelling at ridge crest. Cornice failures can create a large load on the snowpack and trigger persistent weak layers.

Heavy snowfall continues into today, in some areas upwards of a meter of new snow has fallen, accompanied by rising temperatures and strong southwest winds. This is a recipe for very dangerous avalanche conditions. 

In open areas, strong southwest winds will be creating deep deposits of slab in lee areas. In sheltered areas, the new snow will form a touchy storm slab or loose dry problem where it is falling on an inherently weak layer formed by prolonged cold temperatures last week. This drought layer is comprised of near-surface facets and in isolated areas surface hoar sitting on a firm bed surface of hard, wind effected snow, old windslabs.

A weak layer of facets (sugary snow) can be found over a widespread crust that formed in early December (now probably down 100-225 cm). This layer has been most reactive at treeline and low alpine elevations, between 1800-2100 m.

Although we have seen a decreasing trend in avalanche activity on this layer, it has still produced some notable human triggered avalanches over the past week. This problem is particularly hard to predict. We would be very cautious with a large amount of new load overlying this now deeply buried layer that has transitioned into a tricky low-probability high-consequence problem (see the problem description and travel advice for suggestions).

The lower snowpack is well settled. Snowpack depth at treeline ranges from 200-300cm. 

• Stick to simple terrain and be aware of what is above you at all times.
• Avoid all avalanche terrain during periods of heavy loading from new snow and wind.
• Be aware of the potential for large avalanches due to the presence of a buried crust.
• If triggered, storm slabs in-motion may step down to deeper layers and result in very large avalanches.
• Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.