Avalanche Forecast

Issued: Mar 6th, 2018 4:17PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is moderate. Known problems include Persistent Slabs and Cornices.

shorton, Avalanche Canada

Sea To Sky.

A buried weak layer is capable of producing large human-triggered avalanches. Stick to small supported terrain features and be cautious when slopes are getting hit by direct sunlight.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain on Thursday

Weather Forecast

WEDNESDAY: Sunny in the morning with increasing clouds in the afternoon, light southwest wind, freezing level rising to around 1400 m.THURSDAY: Flurries increasing throughout the day with 5-10 cm of snow by the afternoon, moderate southwest wind, freezing level rising to around 1200 m.FRIDAY: Another 5-10 cm of snow with freezing level rising to around 1200 m.

Avalanche Summary

No notable avalanches were reported on Monday, but reports from the weekend highlight a touchy persistent slab problem in this region.Numerous reports of whumpfing around upper treeline elevations were reported, as well as a few large avalanches. An MCR report from the Blackcomb backcountry on Sunday describes a size 3 avalanche that was remotely triggered on a west aspect around 1900 m and presumably failed on the buried surface hoar layer (see photo and details here). A size 2 slab avalanche failed in a north-facing chute at a similar elevation and triggered additional smaller avalanches on nearby slopes. Closer to Squamish, a natural size 2 avalanche failed on a south aspect at 1750 m (see photo and details here). These avalanches highlight a persistent slab problem that exists on all aspects around treeline elevations. This type of problem tends to take a while to heal, and avalanches could remain reactive to human triggers throughout the week.

Snowpack Summary

A thin sun crust has formed on solar aspects and the surface is wind affected in most exposed terrain. Last week's storms buried a weak layer composed of soft facets, surface hoar, and/or crust that is roughly 50-100 cm below the surface. This layer has produced whumpfing, sudden results in snowpack tests, and some remotely triggered avalanches. Lots of the activity has been on buried surface hoar on north aspects at upper treeline elevations. The snowpack is well settled and strong beneath this interface. Variable winds in the past month have produced cornices on many ridgelines. They will become touchier as they grow in size, as temperatures rise, and when they are subject to the strong late-winter sun on clear days.

Problems

Persistent Slabs

A layer of surface hoar, sugary facets, and/or crust is buried 50-100 cm deep and has produced widespread whumpfing, concerning snowpack test results, and a few large remotely triggered avalanches. Upper treeline elevations are the greatest concern.

Minimize exposure to steep, sun exposed slopes when the solar radiation is strong.Choose well supported terrain without convexities.Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 2.5

Cornices

Continued snowfall and strong wind from around the clock has formed large cornices on many ridgelines. Cornices are inherently unstable, unpredictable, and demand respect, especially when the sun is out.

Be careful with wind loaded pocketsGive cornices a wide berth when traveling on or below ridges.Firm cornices may pull back into flat terrain at ridgetop if they fail.

Aspects: North, North East, East, South East, South, South West.

Elevations: Alpine.

Likelihood

Unlikely - Possible

Expected Size

1.5 - 3

Valid until: Mar 7th, 2018 2:00PM