South Columbia

Tricky winter conditions have returned to the alpine. Recent storm snow overlies a touchy weak layer and is reactive to human-triggering. Use a conservative approach to terrain selection.

Fair - Timing, track, or intensity of incoming weather system is uncertain

Unsettled spring conditions are expected on Monday. Mainly cloudy conditions with light flurries (1-4mm) are expected with the possibility of sunny breaks. Alpine winds are forecast to be moderate-strong from the SW. Freezing levels are expected to be around 1000m in the morning and 1800m in the afternoon. A weak storm system is expected to reach the interior early Tuesday morning and is forecast to bring 5-10mm of precipitation to parts of the region during the day. Moderate SW winds in the alpine are forecast to switch to the NW as the front passes. Freezing levels are expected to be around 1200m in the morning and 1500m in the afternoon. A weak ridge of high pressure should bring mainly sunny and dry conditions for Wednesday.

On Saturday, isolated natural avalanche activity was reported up to size 2. Skiers and explosives also triggered avalanches up to size 1.5. These were mainly storm slabs with thickness of 10-30cm. One wind slab was reported to have been triggered remotely from 30m away suggesting that the weak layer is very reactive in some areas. On Monday, lingering storm slabs are expected to be reactive to human-triggering, especially in steep alpine terrain and wind-loaded terrain features. If the sun is out in the afternoon, extra caution should be given to steep sun-exposed slopes.

15-30cm of recent snowfall overlies a weak layer that was buried on Friday. This weak layer typically consists of surface hoar and/or facets overlying a melt-freeze crust that exists everywhere except high elevation north-facing terrain. In exposed alpine terrain, strong SW winds have redistributed the recent storm snow forming thicker wind slabs in leeward features. Large cornices exist in the alpine and may become weak with daytime warming. There are three dormant persistent weak layers that we are continuing to track. The late-March crust is down 30-70cm and was reactive last week during the warm period. The mid-March and mid-February layers are typically down between 60 and 100cm and have been dormant for several weeks. These layers have the potential to wake up with sustained warming, a significant rain event, and/or a big cornice fall.