Avalanche Forecast

Issued: Feb 16th, 2018 5:30PM

The alpine rating is high, the treeline rating is high, and the below treeline rating is considerable. Known problems include Storm Slabs and Persistent Slabs.

Avalanche Canada mgrist, Avalanche Canada

Danger ratings are based on higher snowfall amounts forecast for the south of the region. If you see more than 25cm of new snow consider the danger to be HIGH and avoid all avalanche terrain, free from overhead hazard.

Summary

Confidence

Moderate - Forecast snowfall amounts are uncertain on Saturday

Weather Forecast

The south of this region will see significantly more snow from the storm on Saturday (25-30cm possible). Clearing and becoming cold on Sunday as frigid arctic air moves in. Saturday: Snow (25-30 cm possible in the far south with 10-15 cm near Nakusp). Tree line temperature around -8 Celsius. Winds southwesterly 30km/h.Sunday: Clearing, but lingering flurries possible. Tree line temperatures around -14C. Winds light northeasterly.Monday: Sunny but cold. Alpine temperatures near -18 Celsius. Winds light northerly.

Avalanche Summary

On Friday some locations in the Monashees had locally heavy snowfall amounts resulting in very reactive storm slabs to size 1.5, with crowns 20-40cm thick. On Wednesday, at least five human-triggered avalanches were reported up to size 2 on north, east and south-facing slopes and elevations between 1800 and 2300 m. The releases appeared to be at the base of the most recent storm snow and a crust was reported in some of them, most likely those on more southerly aspects.In Rogers Pass on Monday, skiers remotely triggered a size 3.5 persistent slab avalanche from 40 m away on a south-facing, cross-loaded slope at 2600 m. On the same day, a helicopter remotely triggered a size 3 persistent slab avalanche on a similar aspect/ elevation in the Selkirks a little closer to Revelstoke. Although deeper, persistent avalanche activity is becoming less frequent, these recent avalanches point to the continued reactivity and destructive potential of these layers.

Snowpack Summary

30-40 cm of recent storm snow has settled into a slab in the upper snowpack. Strong winds, most recently from the northwest, shifted these accumulations into deeper, reactive slabs in wind-exposed terrain. These accumulations overlie a mix of older wind slabs in exposed higher elevation terrain, a sun crust on steep solar aspects, a rain crust below 1600m and surface hoar on sheltered slopes.Below the snow surface several persistent weak layers make up a troublesome snowpack. In the top 1.5-2.5 m of the snowpack, two surface hoar/ crust layers buried in January can be found. Expect to find one or the other of these on all aspects and elevations.Deeper in the snowpack (around 200 cm deep) is a facet/crust/surface hoar layer from December, most prevalent at and below treeline.Near the base of the snowpack is a crust/facet combo, most likely to be triggered from thin spots in the alpine.All of these layers have produced large avalanches recently. The wide distribution and ongoing reactivity of these layers suggests that avoidance through choosing simple terrain is the best strategy.

Problems

Storm Slabs

An icon showing Storm Slabs
New storm slabs may be especially reactive in wind-exposed terrain, and could be slow to gain strength due to a mix of underlying weak surfaces. Watch for new wind slab development due to southwest through northwest winds from Friday.
If triggered the storm/wind slabs may step down to deeper layers resulting in large avalanches.The new snow may require several days to settle and stabilize.Avoid all avalanche terrain during periods of heavy loading from new snow, wind, or rain.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible - Likely

Expected Size

1 - 2.5

Persistent Slabs

An icon showing Persistent Slabs
Several troublesome layers exist in the snowpack and may be reactive to large triggers such as a cornice or storm slab release. Human triggering may also be possible in shallow or thin, rocky areas.
Avoid steep convexities or areas with a thin or variable snowpack.Avoid the runout zones of avalanche paths. Very large avalanches have been running full path.Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Feb 17th, 2018 2:00PM