Avalanche Forecast

Northwest Inland

Date issued

Jan 19, 2018 - 5:11 PM

Valid until

Jan 20, 2018 - 2:00 PM

Prepared by

cgarritty

For the safest, best skiing and riding, seek out low density new snow that hasn't formed a slab. Increase your caution at sheltered mid elevations where buried surface hoar may lurk.

Regular season
Friday - January 19, 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

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.

Saturday - January 20, 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

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.

Sunday - January 21, 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

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.

Avalanche Problem 1: Storm Slabs

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

Storm slabs have formed over widespread temperature crusts and more isolated pockets of surface hoar. Slabs are likely to be touchiest where surface hoar is buried as well as in the immediate lee of ridgecrests and exposed terrain features.

Travel and Terrain Advice
  • Sheltered openings at mid elevations are likely areas for surface hoar to be preserved.
  • Avoid areas where the new snow feels stiff and slabby.

Avalanche Summary

Reports from Thursday included one observation of numerous natural storm slab releases from Size 1-2 north of Kispiox. These were noted running on relatively low angle terrain and suspected to have released over a layer of surface hoar that may not be widely distributed. Another few Size 2 natural storm slab releases were noted in very steep north aspects around treeline elevations in the Howsons.

Wednesday's reports included observations of thin (5 cm) storm slabs becoming highly reactive to skier traffic in the Howson Range, producing small remotely triggered (from a distance) and sympathetically triggered (by an adjacent release) slides. These small slabs were also running naturally in any terrain over a 37 degree incline.

Snowpack Summary

Snowfall from the mid-week brought a variable 10-20 cm of new snow to the region. The new snow has buried a temperature crust that likely exists well into the alpine. There are also reports of more isolated pockets of surface hoar beneath the new snow at lower alpine and treeline elevations. This surface hoar is noted in our avalanche activity discussion for having produced numerous storm slab releases in a localized area after the storm ended.

Below the new snow interface, deeper weak layers in the snowpack include a few crusts and surface hoar layers that formed in early January and December. Most recent reports suggest the snow is well bonded to these layers, but snowpack tests in the north of the region have shown some easy results with sudden fracture character, suggesting that a dangerous persistent slab problem may develop as the mid and upper snowpack consolidate into a stiffer slab.

Weather Forecast

Saturday: Mainly cloudy with scattered flurries bringing around 2 cm of new snow, continuing overnight. Moderate south winds. Alpine high temperatures to around -6.

Sunday: Cloudy with continuing flurries bringing 3-5 cm of new snow decreasing overnight. Moderate to strong east winds. Alpine high temperatures to -8.

Monday: Cloudy with continuing light flurries and a trace of new snow. Light southeast winds. Alpine high temperatures to around -8.

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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