Avalanche Forecast

Issued: Jan 21st, 2018 4:35PM

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

mconlan, Avalanche Canada

Cariboos.

A highly complex snowpack is being loaded by new snow and strong winds. Three weak layers are reactive to natural and human triggers. The easy solution is to choose simple terrain free of overhead hazard as the snowpack adjusts.

Summary

Confidence

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

Weather Forecast

MONDAY: Mostly cloudy with intermittent snowfall, accumulation 2-5 cm, moderate to strong southwesterly winds, alpine temperature near -12 C, freezing level near 800 m.TUESDAY: Mostly cloudy with intermittent snowfall, accumulation 1-3 cm, moderate southerly winds, alpine temperature near -10 C, freezing level near 600 m.WEDNESDAY: Mostly cloudy with intermittent snowfall, accumulation 1-3 cm, moderate southerly winds, alpine temperature -7 C, freezing level near 500 m.

Avalanche Summary

Many avalanches were reported on Saturday (with conditions indicated as Spicy). Small to large (size 1 to 3) storm slabs and wind slabs were noted on Saturday, being triggered naturally, by skiers, snowmobiles, and explosives. The avalanches released generally on lee slopes (northerly to easterly) at all elevation bands, ranging from 30 to 90 cm deep. Many of the avalanches released on the persistent weak layers described in the Snowpack Summary. Similar avalanches were observed on Thursday and Friday.

Snowpack Summary

The current snowpack is complex, we now have three active weak layers that we are monitoring. 20-50 cm of storm snow sits on a newly formed crust and/or surface hoar layer (mid-January). Prior to the storm the crust was reportedly widespread; high elevation north is likely one of the few crust-free zones. The mid-January surface hoar is up to 10 mm and reported at all elevation bands. The new snow fell with strong southwesterly winds, producing wind slabs in lee features. Deeper in the snowpack, the early-January persistent weak layer is 30 to 70 cm below the surface. It is composed of surface hoar on sheltered slopes and sun crust on steep solar aspects and found at all elevation bands. Snowpack tests show sudden fracture characters with moderate loads and high propagation potential, as well as whumpfs and cracking. Another weak layer buried mid-December consisting of a facet/surface hoar/crust combination is buried 40 to 100 cm deep. It is most problematic at and below tree line.A rain crust buried in November is 100 to 150 cm deep and is likely dormant for the time being.

Problems

Storm Slabs

Around 40 cm of new snow has formed a slab that sits on a weak layer composed of feathery surface hoar and/or a crust. Expect the slab to be deeper in lee features due to strong south winds. The slab is sensitive to both natural and human triggers.

If triggered, the storm/wind slabs may step down to deeper layers, resulting in large avalanches.Be very cautious as you transition into wind affected terrain, wind slabs may be deep and touchy.Avoid exposure to terrain traps where the consequence of a small avalanche could be serious.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

1 - 2.5

Persistent Slabs

Three persistent weak layers are lurking in our snowpack, which remain capable of producing very large and destructive avalanches. Keep the terrain choices reined in as the snowpack adjusts to the new load.

Avoid open slopes and convex rolls where buried surface hoar may be preserved.Numerous large avalanches have run on these layers in well-supported, treed terrain.Good day to make conservative terrain choices and watch for clues of instability.

Aspects: All aspects.

Elevations: All elevations.

Likelihood

Likely

Expected Size

2 - 3.5

Valid until: Jan 22nd, 2018 2:00PM