Avalanche Forecast

Cariboos

Date issued

Jan 20, 2018 - 4:39 PM

Valid until

Jan 21, 2018 - 2:00 PM

Prepared by

mconlan

Sundays storm could drop 30 cm of snow with strong winds, onto a highly complex snowpack. 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.

Regular season
Saturday - January 20, 2018
Alpine

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Treeline

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Below Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Sunday - January 21, 2018
Alpine

4 - High

Very dangerous avalanche conditions.Travel in avalanche terrain not recommended.

Natural avalanches likely;human-triggered avalanches very likely.

Large avalanches in many areas;or very large avalanches in specific areas.

Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Below Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Monday - January 22, 2018
Alpine

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Below Treeline

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation,cautious route-finding and conservative decision-making essential.

Natural avalanches possible;human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

Avalanche Problem 1: Storm Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

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 winds. The slab is sensitive to both natural and human triggering.

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

Avalanche Problem 2: Persistent Slabs

What Elevation?
Which Slopes?
Chances of Avalanches?
Expected Size?

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.

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

Avalanche Summary

On Friday, there were several reports of small to large (size 2 to 3) persistent slab avalanches, triggered naturally and by skiers and snowmobilers. They were about 90 cm deep on northerly aspects at all elevations. Expect similar avalanches to release on all aspects with new load.

On Thursday, avalanche activity was reported as storm and persistent slabs. Storm slabs were running to size 2 on southerly and northerly aspects in the alpine and tree line. There were two persistent slab avalanches reported that were both skier triggered 80cm deep between 1100 and 1400m on north aspects. One of them was remotely triggered (from a distance) from 60m away and was a size 2.5. The other was triggered by a ski cut and was a size 1, yet still 80cm deep.

On Wednesday, a small natural avalanche cycle was reported from steep ridge features. Fast and loose sluffing was also reported.

Snowpack Summary

The current snowpack is complex, we now have three active weak layers that we are monitoring.

15-40 cm of storm snow and another 10-30 cm of forecasted snow for Sunday 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 is falling with strong southwesterly winds, producing wind slabs in lee features. Deeper in the snowpack, the early-January persistent weak layer is 30 to 60 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.

Weather Forecast

SUNDAY: Cloudy with snowfall, accumulation 15-30 cm, strong to extreme southwesterly winds, alpine temperature -8 C, freezing level near 900 m.

MONDAY: Mostly cloudy with light snowfall, accumulation 2-5 cm, light to moderate southwesterly winds, alpine temperature near -9 C, freezing level near 800 m.

TUESDAY: Partly cloudy with intermittent snowfall, accumulation 1-3 cm, light to moderate southwesterly winds, alpine temperature near -10 C, freezing level near 600 m.

Danger Ratings Explained

1 - Low

Generally safe avalanche conditions. Watch for unstable snow on isolated terrain features.

Natural and human-triggered avalanches unlikely.

Small avalanches in isolated areas or extreme terrain.

2 - Moderate

Heightened avalanche conditions on specific terrain features. Evaluate snow and terrain carefully; identify features of concern.

Natural avalanches unlikely; human-triggered avalanches possible.

Small avalanches in specific areas; or large avalanches in isolated areas.

3 - Considerable

Dangerous avalanche conditions. Careful snowpack evaluation, cautious route-finding and conservative decision-making essential.

Natural avalanches possible; human-triggered avalanches likely.

Small avalanches in many areas; or large avalanches in specific areas; or very large avalanches in isolated areas.

4 - High

Very dangerous avalanche conditions. Travel in avalanche terrain not recommended.

Natural avalanches likely; human-triggered avalanches very likely.

Large avalanches in many areas; or very large avalanches in specific areas.

5 - Extreme

Avoid all avalanche terrain.

Natural and human-triggered avalanches certain.

Large to very large avalanches in many areas.

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