New snow, strong winds and mild temperatures have been a recipe for reactive storms slabs and rapid cornice growth. As winds ease Tuesday, recently wind-loaded features will likely remain sensitive to human triggering.
Continued flurries and gusty winds will contribute to an ongoing storm slab problem. Strong to extreme winds have scoured windward aspects and pressed moist snow into slabs in leeward terrain. Expect to find the most reactive deposits in open areas and around ridge features at treeline and above.
Explosives testing continues to periodically trigger a weak layer of snow at the bottom of the snowpack. Two such occurrences were observed on January 22 up to size 3.5. This deep persistent layer has proven that if triggered, it will produce very large and destructive avalanches.
Monday night: Snow, 5-20 cm with Whistler on the low end of the range. Alpine low -3 C. Strong southeast to southwest winds. Freezing level 1000-1200 m.
Tuesday: Broken cloud with flurries bringing up to 5 cm. Alpine high -2 C. Light southwest winds. Freezing level 1200-1400 m.
Wednesday: Snow, 10-20 cm. Alpine high -1 C. Strong southerly winds, approaching extreme southwest at ridgetop. Freezing level 1000-1200 m.
Thursday: Mix of sun and cloud with flurries in the evening. Alpine high -2 C. Light to moderate southwest winds. Freezing level 700-1000 m.
Explosive control work Sunday produced mostly size 1 storm slabs and up to size 2 cornice/slab avalanches with up to 75 m wide propagation. Natural windslab and cornice failures up to size 1.5 were observed in lee and cross-loaded alpine terrain.
A few large to very large (size 2-3) natural storm slab avalanches were observed in the Whistler backcountry on Saturday morning, and explosives triggered storm slabs and cornice-triggered avalanches up to size 2.
Strong to extreme winds have left a variety of wind-affected surfaces in alpine and open treeline areas. Windward slopes are scoured down to the January 20 crust. On leeward terrain, moist surface snow has been pressed into slabs over the crust, and notable cornice growth has been observed at ridgetops. Overnight snowfall sits over a crust below 1700 m and on south facing slopes treeline and above.
Weak faceted grains and crusts near the base of the snowpack continue to be a concern in inland parts of the region such as the Spearhead Range.
