Backcountry Advisory 

As of Wednesday, April 13

Alpine: CONSIDERABLE

Treeline: CONSIDERABLE

Below Treeline: MODERATE

Travel Advisory : April has ushered in the most enjoyable snow conditions of the winter and since the beginning of the month we have received about 150 cm at the 1,650 metre weather plot on Whistler Mountain. The winds accompanying the major storms have been consistently strong from 90 to 180 degrees (east through to south). Between storm cycles there has been some wind transport of the surface snow. Cornices are beginning to take on a normal winter look and they are failing with little or no trigger.

During the week of April 4, these factors finally combined to provide enough of a load to stress the snowpack weaknesses that formed earlier in the season around the late January and early March rain crusts. Numerous large avalanches to size 3.5 have been observed on all aspects during the past 10 days. Some have initiated with large triggers (cornice fall, explosives), while others have required very little in the way of an overload. Most have been on north quadrant aspects with steep/rocky start zones or an unsupported convex roll. These large occurrences are becoming increasingly difficult to predict – in some cases the slope will continue to tolerate a load until something or someone hits the exact "sweet spot" or until a bit more snow falls.

If you are heading into the backcountry, stick to the very mellow terrain and avoid traveling under large slopes that could be triggered by a cornice fall from above. The avalanches that we have seen so far may only be the tip of the iceberg. Remember that even if you think you are traveling as safely as possible, someone above you may not be.

Avalanche Activity : Explosive testing and ski cutting on Whistler and Blackcomb have been producing numerous storm snow avalanches and some deeper slabs that are running on the January and March crusts. In some cases the avalanches appear to have initiated in the storm snow and then stepped down once or twice to old facetted crystals around one of the crusts.

A couple of interesting avalanche events occurred on April 12. On Cowboy Ridge the seventh skier on the slope triggered a 75 cm slab that carried him to the bottom of the slope and straight into the bar. At this time the sliding layer in unknown.

On Whistler Mountain, in the Flute area, a small piece of cornice or maybe even the sonic waves from a bomb hung over the cornice triggered a size 3 avalanche that ran into a favourite snowboard jump site. The NNE facing rocky slope had been well controlled with explosives the previous day and had been skied (there were four sets of previous tracks over the 80-180 cm crown line). Perhaps a bit of overnight wind-transported snow was enough to tip the balance. The failure plane was a layer of facets within the March crust.

Snowpack : The March 8 melt-freeze crust is in most areas well buried below a variable depth of snow and the late January crust is even deeper. You may find a softer layer of old facetted crystals sitting on or within both of these crusts. Depending on aspect and elevation, the storm snow is made up of variable layers that in some spots include weak melt-freeze crusts. The storm snow layers have been settling and tightening in with time after the storms. The deeper weakness are a bit of a time bomb and can be expected to continue performing.

As is usual at this time of year, any available loose surface snow will be easily moistened by exposure to the sun and may begin to sluff naturally.

Weather : Unsettled conditions are expected to persist until Friday when another Pacific system may be upon us. Temperatures are expected to remain cool but may climb up a bit with the arrival of the storm.

Conditions may change rapidly so try to keep up with most current information. Call 604-938-7676 or see the Whistler-Blackcomb website for local advisories (they are updated by the mountain forecasters as quickly as possible). Province wide info can be obtained from the CAA at avalanche.ca. If you are proceeding into avalanche terrain, travel with extreme caution. The avalanche danger will rise with warming and/or more snowfall.

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