Just when we all thought that summer had kicked in early with a vengeance, Mother Nature dumped 20 cm of low density new snow on the mountains on May 28 and 29. The snow rapidly lost its winter-like quality, but that didn't stop the late season die-hard skiers and riders from enjoying the turns. In spite of the moderate to strong S and SW winds associated with the snowfall, very little in the way slab formation was noted on Whistler Mountain on May 29. However sluffing and snowballing did begin to occur naturally with the first brief glimpses of sunshine.
Forecast further warming on Thursday could moisten the full depth of storm snow and cause even more significant sluffing. Given a long smooth slope and the underlying melt freeze crust, a considerable volume of "schmoo" could become entrained in the sluff. The long range forecast is calling for another brief return to winter on the mountains over the weekend with a series of unseasonably cool systems arriving in our region beginning on Friday.
Last week's record high temperatures produced numerous deep slab avalanches in the backcountry. Most appeared to have been triggered by cornice fall, and the suspected failure plane was the November facet layer. In several cases, the slab ran to the ground. We can expect to see renewed activity of this nature when the temperatures warm again and the critical crusts within the snowpack are destroyed. When this happens, the mountains are not the place to be!
As of May 30, the backcountry avalanche danger is rated as MODERATE. This will increase with daytime warming and sunshine. Check for the most current information before you plan to head out.