Avalanche Forecast

Northwest Inland

Date issued

Jan 23, 2018 - 4:48 PM

Valid until

Jan 24, 2018 - 2:00 PM

Prepared by

jmcbride

Wind and storm snow have formed reactive slabs particularly on leeward and open slopes at upper elevations. Deeper weak layers also remain a concern on isolated features at lower elevations.

Regular season
Tuesday - January 23, 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.

Wednesday - January 24, 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.

Thursday - January 25, 2018
Alpine

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.

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.

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 have also created pockets of wind slab in exposed areas treeline and above.

Travel and Terrain Advice
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Use caution on open slopes and convex rolls at treeline where buried surface hoar may be preserved.

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 lower elevations.

Travel and Terrain Advice
  • Watch for signs of instability such as whumpfing, or cracking at lower elevations.

Avalanche Summary

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 Saturday included one remotely (from a distance) triggered Size 1.5 wind slab releasing from a steeper northwest-facing slope at around 1500 m. The slab depth was 40-60 cm.

Friday's reports 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. Another report from last week mentioned numerous natural storm slab releases from Size 1-2 north of Kispiox. These were suspected to have released over a layer of surface hoar that may not be widely distributed.

Snowpack Summary

Recent light snowfalls have gradually brought about 20-40 cm of new snow to 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 at lower alpine and treeline elevations. While its distribution is uncertain, this surface hoar remains an ongoing concern as the overlying storm snow settles into a slab above it.

Below the mid-January interface, deeper weak layers in the snowpack include crusts and surface hoar layers that were buried in early-January and mid-December. Most recent reports suggest the old snow is well bonded to these layers, but 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: Flurries. Accumulation up to 5 cm. Ridge wind moderate, southeast. Temperature -9. Freezing level valley bottom.

WEDNESDAY: Flurries. Accumulation 2-7 cm. Ridge wind light, south. Temperature -6. Freezing level 300 m.

THURSDAY: Mainly cloudy, light flurries. Accumulation trace. Ridge wind light, east. Temperature -8. Freezing level valley bottom.

FRIDAY: Mostly cloudy, light flurries. Accumulation up to 2 cm. Ridge wind light, south. Temperature -9. Freezing level valley bottom.

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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