Backcountry Advisory 

As of Wednesday, March 21

A mere days away from the official onset of spring, we finally got hit by one of those "____ kicker" winter storms that the West Coast is known for. New snowfall for the storm amounted to about 35-40 cm in the alpine terrain. Mountain top winds gusted over 150 km/h, wreaking havoc on the ski hills, and creating some interesting snow conditions. The freezing level jumped up to about 1,600m at the height of the storm, but rapidly fell with the frontal passage. The lingering "power flurries" left us with a bit of icing on the cake.

Immediately following the storm, operators throughout the Whistler/Duffey corridor noted signs of natural activity that had occurred. Some of the larger releases were suspected to have failed down in the November facet layer, although the potential for huge windslab formations during the storm made it difficult to precisely determine sliding layers from a distance. On Whistler and Blackcomb, ski and explosive testing produced for the most part isolated size 1-2 results involving the storm snow layers. A couple of surprise anomalies did however pop up. One on a west aspect at 2,050 m and the other on a south aspect at a similar elevation. Both of these larger avalanches failed on a strong melt freeze crust that dates back to the warm sunny weather earlier in the month.

The surface hoar layer that was cropping up on north aspects at treeline elevations is in some areas buried more that 100 cm below the surface. It is still a concern, especially now that for the unaware, it may be hidden well below the range of a quick test profile. If you are travelling in terrain where this layer may have been preserved, take the time to find it and to take a good look at the overlying layers. In shallow, rocky terrain, the November facets will continue to loom until the snowpack has disappeared. Predicting exactly what will trigger the slab is the big question – a person, another storm, a cornice fall, or maybe just a brief glimpse of the sun? As explained earlier, caution should be exercised also on slopes that were well cooked during the late February/early March heat wave. The storm snow layers will continue to tighten up with time. Beware though of hollow sounding slabs that allow little in the way of ski penetration. They may seem solid, but sometimes it only takes punching through a shallower part of the slab to trigger the whole slope. The resulting debris could be very hard and chunky. Remember too that conditions at this time of year may change drastically throughout the day. A slope safely travelled in the morning hours may not be such a good idea after the sun has been on it for a few hours. Keep in mind that warming of the overlying slab will aggravate any underlying weaknesses.

The forecast sunny end to the week will encourage an exodus into the mountains. If you plan on heading out, try to get as much information as possible regarding the specific terrain that you intend to frequent. Even within the Sea to Sky Corridor, conditions may be variable from one valley to the next. Add this to the mix created by sunshine, wind transport and bouncing freezing levels, and you end up with a myriad of possibilities. Travel with caution.

The backcountry avalanche danger as of March 21 is rated CONSIDERABLE trending to MODERATE. The snow stability will deteriorate with daytime warming.

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