Avalanche Forecast

Issued: Feb 12th, 2018 4:57PM

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

jmcbride, Avalanche Canada

North Columbia.

A strong system with periods of intense snowfall and high winds will increase avalanche danger on Tuesday. Stick to low-angle, simple terrain and avoid areas with overhead hazard. Large avalanches may run long distances.

Summary

Confidence

Moderate - Intensity of incoming weather systems is uncertain

Weather Forecast

TUESDAY: Snow. Accumulation 10-20 cm. Ridge wind moderate to strong, southwest. Temperature -10. Freezing level valley bottom.WEDNESDAY: Mostly cloudy, light flurries. Accumulation trace. Ridge wind light, west. Temperature -10. Freezing level valley bottom.THURSDAY: Mix of sun and cloud. Ridge wind light, south. Temperature -12. Freezing level valley bottom.

Avalanche Summary

Monday skiers remotely triggered (from a distance) a size 3.5 from 40 m away on a ridgeline adjacent to a south-facing slope at 2600 m.On Sunday explosive control work north of Revelstoke produced storm slab results from size 1.5-2.5 and two size 3 deep slab failures (120-170 cm deep) on a east aspect at 2400 m.A very large, widespread avalanche cycle was observed on Thursday, with a few events continuing on Friday and Saturday. Slopes of all aspects and elevations ran full path and reached valley floor. In some cases, mature timber was smashed. These failed on all of the persistent weak layers discussed in the snowpack section. Avalanches involving only the recent storm snow were also very large. Explosives continued to produce very large persistent slabs on Saturday.

Snowpack Summary

Strong north to north-westerly winds have shifted 25-70 cm recent storm snow into wind slabs on lee slopes. Alpine and open treeline areas have seen extensive wind-affect, while a sun crust exists on solar aspects and a rain crust can be found below 1600 m.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 layers buried in January can be found. Expect to find one or 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

New snow and wind will form touchy storm slabs. These slabs will cover a variety of old surfaces including extensive wind slabs at upper elevations and crusts on solar aspects and at lower elevations. Pay attention to how the new snow is bonding.

If triggered, wind slabs may step down to deeper layers resulting in large avalanches.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely - Very Likely

Expected Size

1 - 2.5

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.

Minimize exposure to overhead avalanche terrain, large avalanches may reach the end of runout zones.Be aware of the potential for large, deep avalanches.Avoid steep convexities or areas with a thin or variable snowpack.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Possible

Expected Size

2 - 4

Valid until: Feb 13th, 2018 2:00PM