Avalanche Forecast

Lizard Range and Flathead

Date issued

Jan 26, 2018 - 4:43 PM

Valid until

Jan 27, 2018 - 2:00 PM

Prepared by

jmcbride

The combination of recent heavy snowfall and buried weak layers has created very dangerous avalanche conditions. Several large, destructive avalanches have occurred in the past week. Travel in avalanche terrain is not recommend.

Regular season
Friday - January 26, 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.

Saturday - January 27, 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.

Sunday - January 28, 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

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.

Avalanche Problem 1: Storm Slabs

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

New snow and has formed touchy storm slabs, while winds are building cornice and loading lee slopes near ridge top. These slabs have shown the potential for wide propagations and running long distances.

Travel and Terrain Advice
  • If triggered, storm slabs may step down to deeper layers and result in large avalanches.
  • Choose low-angle, well supported terrain without convexities.

Avalanche Problem 2: Persistent Slabs

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

Several weak layers of concern are buried within the snowpack and produced several recent large and very large avalanches. Simple terrain with low angle, supported slopes is a good choice.

Travel and Terrain Advice
  • Watch for signs of instability such as whumpfing, or shooting cracks.
  • Avoid exposure to overhead avalanche terrain, large avalanches may reach the end of run out zones.

Avalanche Summary

Several large and very large avalanches have occurred in the past five days highlighting that very dangerous avalanche conditions exist within the region.

Explosive control work on Friday produced numerous large and one very large, Size 4, deep slab avalanche that failed on the mid-December layer, 250 cm deep, on a northeast slope at 2100 m. This avalanche destroyed several large trees and ran well below treeline to the full extent of the runout zone.

On Wednesday and Thursday, numerous natural, skier and explosive triggered storm slab avalanches up to Size 3 were reported with crowns from 20-80 cm deep, and propagations from 20 up to 150 m wide.

On Tuesday a Size 2 was triggered from 50 m away by a snow machine on a northeast aspect at 2050 m. The crown was 120 cm deep and is suspected to have failed on the mid-December weak layer.

Reports from Monday included seven deep persistent slabs that were released with small explosives in the alpine in the Fernie area. Sizes ranged from 2.5-3, crown depths averaged about 200 cm and all results indicated the deeply buried late-November crust as the failure plane.

Snowpack Summary

About 60-80 cm of settled storm snow now covers a layer of surface hoar on sheltered aspects (especially prominent from 1400-1900 m) and sun crust on solar aspects, that was buried mid-January.

Beneath the mid-January interface lie a number of very concerning buried weak layers. A layer of surface hoar from early-January is buried 90-110 cm below the surface. A weak layer buried mid-December (predominantly surface hoar and/or a sun crust) is around 120-160 cm below the surface at treeline and below treeline elevations. A rain crust with sugary facets that developed late-November is near the bottom of the snowpack and is now buried 200-250 cm below the surface.

All of these layers remain active and have produced recent large, destructive avalanches.

Weather Forecast

TONIGHT: Cloudy, light flurries. Accumulation 3-8 cm. Ridge wind light, southwest. Temperature -10. Freezing level valley bottom.

SATURDAY: Cloudy, flurries. Accumulation 5-10 cm. Ridge wind light to moderate southwest. Temperature -4. Freezing level valley bottom.

SUNDAY: Cloudy, light flurries. Accumulation trace. Ridge wind light southwest. Temperature -4. Freezing level valley bottom.

MONDAY: Cloudy, flurries. Accumulation 5-15 cm. Ridge wind strong, southwest. Temperature +1. Freezing level rising to 1900 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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