Avalanche Forecast

South Coast Inland

Date issued

Dec 31, 2017 - 5:16 PM

Valid until

Jan 1, 2018 - 2:00 PM

Prepared by

ghelgeson

Human triggered slab avalanches may become more likely as warm temperatures allow the storm snow to settle into a more cohesive slab. Keep a close eye on steep sun exposed slopes throughout the day too, warming may initiate natural loose avalanches.

Regular season
Monday - January 1, 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.

Tuesday - January 2, 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.

Wednesday - January 3, 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

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.

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?

50 to 80 cm of new snow has fallen in the last few days accompanied by wind mainly out of the south. Human triggered avalanches may become more likely as time, warm temperatures and wind loading allow the snow to settle into a more cohesive slab.

Travel and Terrain Advice
  • As the storm slab problem gets trickier, the easy answer is to choose more conservative terrain.
  • Caution with open slopes and convex rolls at and below treeline, buried surface hoar may be present.
  • Avoid wind loaded terrain at and above treeline, especially near ridge crests and roll-overs.

Avalanche Problem 2: Loose Wet

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

Loose moist avalanches may run naturally on steep sun exposed slopes as previously cold snow is introduced to warm temperatures for the first time on Monday.

Travel and Terrain Advice
  • Avoid sun exposed slopes especially if the snow is moist or wet.
  • Minimize exposure to solar aspects overhead, loose avalanches could travel surprisingly far.
  • Stay in tune with the physical environment, conditions may change throughout the day.

Avalanche Summary

On Saturday a widespread avalanche cycle to size 1.5 was reported with avalanches failing within the recent storm snow.  A natural avalanche cycle likely occurred Friday night during the storm and may have continued into early Saturday morning.

Snowpack Summary

Friday night's storm produced about 30 cm in the north of the region and almost 40 cm in the south. That brings the total from the two successive storms to approximately 50 to 80 cm. The bulk of the wind during the storms was out of the southwest, south and southeast but there were periods of northeast and easterly winds too. All of this new snow rests on a variety of old surfaces including crust on solar aspects, old wind slabs, facets and isolated surface hoar below treeline. Wind slabs are common in wind exposed terrain, but it's thought the snow is largely unconsolidated in protected areas. As temperatures begin to warm on Monday the storm snow will likely settle into a more cohesive slab.

A widespread melt-freeze crust buried mid-December exits throughout the region. This crust is down around 30 to 60 cm in the Duffey. Around the Coquihalla it's about 100 cm below the surface. This layer has not produced much in the way of avalanche activity, but it could come to life as the overlying slab gains cohesion.

Beneath the mid-December crust, the lower snowpack is generally strong and well settled.

Weather Forecast

A warm dry pattern is expected for the next few days. The upper ridge will shift eastward on New Year's Day, which opens the door to warm air drifting in from the eastern pacific. This pattern is expected to stick with us for the foreseeable future.

MONDAY: Temperature Inversion with below freezing air in the valley, above freezing (warmer) air between 1700 m and about 2500 m. Scattered cloud, light variable wind, no snow expected.

TUESDAY: Temperature Inversion with below freezing air in the valley, above freezing (warmer) air between 1500 m and about 2800 m. Scattered cloud, light southwest wind, no snow expected.

WEDNESAY: Temperature Inversion with below freezing air in the valley, above freezing (warmer) air between 1500 m and about 2800 m. Clear skies at dawn, a few clouds in the afternoon, light southwest wind, no snow expected.

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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