Avalanche Forecast

Scattered flurries leading up to a big storm on Sunday.

FRIDAY NIGHT: Cloudy with isolated flurries and up to 5 cm of snow, moderate west wind, treeline temperatures around -6 C.

SATURDAY: Cloudy with isoalted flurries and up to 5 cm of snow, moderate west wind with strong gusts, treeline temperatures around -6 C.

SUNDAY: Snow throughout the day with 10-15 cm in northern parts of the region and 15-25 cm in southern parts of the region, strong southwest wind, freezing level climbing to 1400 m with treeline temperatures reaching -2 C.

MONDAY: 5-25 cm of snow (more in the south), strong southwest wind, treeline temperatures drop to -4 C.

Preliminary reports from Friday suggest new wind slabs are becoming reactive (MIN report). Reports between Tuesday and Thursday were limited to some small (size 1) wind slabs reactive to skiers in northern parts of the region and some small loose avalanches on steep sun-exposed slopes.

Earlier in the the week and last weekend there was evidence of some larger (size 2) natural avalanches from in southern parts of the region such as Cheam (MIN report) and the Coquihalla (MIN report). These avalanches appeared to have failed in storm and wind interfaces, and did not step down to any weak layers. Last weekend there were several reports of large (size 2-3) natural wind slab avalanches, as well as some human triggered avalanches such as this notable avalanche on Matier in the Duffey (MIN report). A notable size 3 (very large) persistent slab was remotely triggered (from a distance) by skiers in the McGillivray Pass on Feb 8. This occurred on a southwest aspect at 2400 m and was described as a hard wind slab formed over our facet layer from late January. These older wind slabs are trending towards being unreactive.

As of Friday afternoon there is 10-20 cm of new snow above a widespread interface that may become a reactive failure layer for storm and wind slab avalanches over the weekend. This interface consists of a sun crust on steep south slopes and faceted snow on polar aspects. In many areas there are old buried wind slabs that have become hard and mostly unreactive. These wind slabs were deposited in unusual places after a strong bout of northeast wind last week.

Persistent weak layers have trended towards being unreactive and vary by location within the region:

• In the south, the primary feature, found at treeline and below in the Allison Pass area, is a melt-freeze crust from mid-January, about 40-60 cm deep. Although this layer is present in the Coquihalla snowpack (60-80 cm), it has been less problematic in that area recently.
• In the north, the old wind slabs discussed above were reactive last week to skier triggering on early February interfaces of surface hoar (think shaded aspects) and sun crusts (think solar aspects). 
• Also in the north, older weak layers may still linger in shallow rocky terrain. This includes an old layer of faceted snow (Jan 24) roughly 50-70 cm deep and a melt-freeze crust from early December 100-200 cm deep. These deeper layers have not been reactive recently.

• Back off steep and aggressive lines, stick to simple terrain.
• Seek out sheltered terrain where new snow hasn't been wind-affected.
• Recent new snow may be hiding windslabs that were easily visible before the snow fell.
• Be aware of highly variable recent wind loading patterns.
• Closely monitor how the new snow is bonding to the old surface.