Avalanche Forecast

Northwest Inland

Date issued

Jan 25, 2018 - 4:31 PM

Valid until

Jan 26, 2018 - 2:00 PM

Prepared by

jmcbride

Watch for areas where wind and storm snow have formed cohesive slabs above the recently buried crust/ surface hoar layer.  A release near the surface may step down to a deeper layer.

Regular season
Thursday - January 25, 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

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.

Below Treeline

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.

Friday - January 26, 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

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.

Below Treeline

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.

Saturday - January 27, 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?

Recent storm snow has formed reactive slabs above the most recent crust/ surface hoar interface. Winds earlier in the week have also created pockets of wind slab in leeward areas in the alpine and at treeline.

Travel and Terrain Advice
  • Caution on steep slopes and convex rolls at where a crust/surface hoar layer has been buried.
  • Be careful with wind loaded areas, especially near ridge crests and roll-overs.

Avalanche Problem 2: Persistent Slabs

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

Weak layers buried in the snowpack have produced recent avalanches with very light triggers particularly on unsupported features at treeline and below.

Travel and Terrain Advice
  • Watch for signs of instability such as whumpfing, or cracking at lower elevations.
  • Avoid shallow or thick to thin snowpack areas where triggering a deeper layer is more likely.

Avalanche Summary

On Wednesday there was a report of a skier-triggered Size 1 wind slab avalanche on a northwesterly aspect at 1650 m in the northern part of the region, east of Ningunsaw.

Tuesday there were reports of easily-triggered wind slabs 30-40 cm deep releasing to Size 1 in wind-loaded areas near ridge crests in the alpine in the southern part of the region.

On Monday there were reports from areas north of Kispiox of reactive storm slabs up to size 1.5 and 25 cm deep releasing with skier traffic on steeper, convex terrain.

Reports from late last week showed a notable increase in persistent slab activity at lower elevations in the Howson Range. In this area, three Size 2 releases failed on steeper terrain with remote triggers on the mid-December weak layer, found 50 cm below the surface.

Snowpack Summary

Recent light snowfalls have gradually brought from 20-60 cm of new snow across the region. This new snow has buried the mid-January interface which features a crust that exists well into the alpine and isolated pockets of surface hoar in sheltered areas at lower alpine and treeline elevations.

Below the mid-January interface, deeper weak layers in the snowpack include crusts and surface hoar layers that were buried late-December and mid-December and now lie 50-80 cm below the surface.

Recent persistent slab activity over a surface hoar and facet 'combo' at low elevations suggests that a dangerous persistent slab problem may be developing as the mid and upper snowpack consolidate into a stiffer slab over this layer.

Weather Forecast

TONIGHT: Light flurries. Accumulation trace. Ridge wind light, southeast. Temperature -12. Freezing level valley bottom.

FRIDAY: Cloudy, light flurries. Accumulation trace. Ridge wind light, southwest. Temperature -11. Freezing level valley bottom.

SATURDAY: Mix of sun and cloud. Ridge wind light to moderate, east. Temperature -12. Freezing level valley bottom.

SUNDAY: Snow. Accumulation 5-15cm. Ridge wind strong, southeast. Temperature -12. Freezing level valley bottom. Alpine inversion.

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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