Avalanche Forecast

Issued: Apr 6th, 2018 5:28PM

The alpine rating is moderate, the treeline rating is moderate, and the below treeline rating is low. Known problems include Persistent Slabs and Wind Slabs.

ghelgeson, Avalanche Canada

Cariboos.

A mid-winter snowpack at and above treeline requires thoughtful terrain selection. We can't forget about the potential for large human triggered slab avalanches that are most likely on south facing terrain at upper elevation.

Summary

Confidence

High -

Weather Forecast

The struggle between "spring-like" and "Arctic-like" will continue for a few more days. Saturday's storm is not expected to produce much snow in the Cariboos. A more spring-like pattern begins to take shape on Sunday with freezing levels creeping towards 2000 m by Monday.SATURDAY: Broken cloud cover, freezing level beginning near valley bottom rising to around 1500 m, light to moderate south/southwest wind, 1 to 2 cm of snow possible. SUNDAY: Broken cloud cover, freezing level beginning near valley bottom rising to about 1600 m, light west/southwest wind, 1 to 2 cm of snow possible. MONDAY: Scattered cloud cover, freezing level beginning around 1500 m rising to about 2000 m, light to moderate west/southwest wind, trace of snow possible.

Avalanche Summary

Reported avalanche activity on Thursday was limited to a size 2 natural cornice failure on a southeast facing slope at 2900 m. On Wednesday a natural size 3 cornice failure was observed on an unknown aspect, the cornice did not initiate any other avalanche activity. Small loose dry sluffing was also observed on south facing aspects between 1500 and 2100 m suggesting that the cool temperatures are preserving cold snow, even on southerly aspects.Explosives control in the region yielded several persistent slab (size 3) and shallower storm slab (size 1.5) releases on north to northeast aspects in the alpine on Monday. Persistent slabs had 90 cm fracture depths with the shallower storm slabs at 40 cm.

Snowpack Summary

Last week's storms brought 60 to 100 cm of new snow to the region. The snowfall was initially accompanied by strong south winds and then followed by strong north winds, so a mix of old/stubborn and newer, more reactive wind slabs can now be found on a range of aspects at higher elevations. In sheltered areas, this storm snow has been gradually settling into a slab above a persistent weak layer buried in mid-March that consists of crusts at low elevations and on south aspects, and surface hoar on shaded aspects at higher elevations. The structure of storm snow above this layer isn't uniform, however, and recent storm slabs have been observed running on an interface down about 40 cm as well as at the late-March crust. Other persistent weak layers from early January and mid-December are still being reported by local operators, but are generally considered dormant.

Problems

Persistent Slabs

Weak layers of crust and surface hoar from last month are now buried up to 90 cm deep and have shown prolonged reactivity since the last storm. Manage the uncertainty around triggering these layers by sticking to lower angle, supported slopes.

Minimize exposure to steep planar south-facing slopes - especially if they see sunshine.Use caution around sheltered steep or convex slopes where buried surface hoar may be preserved.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1.5 - 3

Wind Slabs

Strong and shifting winds have blown loose snow into wind slabs on a wide range of aspects in wind-affected areas. Moderate southerly winds Saturday may from fresh wind slabs in north facing terrain immediately lee of ridge crest.

If triggered the wind slabs may step down to deeper layers resulting in large avalanches.Be especially careful with wind loaded pockets near ridge crests and roll-overs.

Aspects: All aspects.

Elevations: Alpine, Treeline.

Likelihood

Possible

Expected Size

1 - 2

Valid until: Apr 7th, 2018 2:00PM