Avalanche Forecast

South Coast Inland

Date issued

Dec 30, 2017 - 5:01 PM

Valid until

Dec 31, 2017 - 2:00 PM

Prepared by

ghelgeson

Sunday offers one last day of cool temperatures before warming arrives Sunday night. Pay attention to how the snow feels underneath you, as the storm snow settles into a more cohesive slab it will likely become more sensitive to human triggering.

Regular season
Saturday - December 30, 2017
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.

Sunday - December 31, 2017
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.

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

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?

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

Avalanche Summary

No new avalanche activity was reported from Friday. A natural avalanche cycle likely occurred Friday night during the storm and may have continued into early Saturday morning. On Thursday a natural avalanche cycle was reported on steep unsupported features which produced storm slabs up to size 1.5 with crowns 10 to 15 cm in depth. A skier triggered size 1.5 avalanche on an unsupported feature at treeline was also reported.

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 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

After a succession of snowstorms over southern BC, the weather over the lower mainland will settle into a dry period as 2017 comes to an end and 2018 begins. All indications point to the dry spell lasting until at least mid-week.

SUNDAY: A few clouds, freezing level at valley bottom with an Above Freezing Layer (AFL) forming between 1800 m and 2500 m in the late afternoon. Moderate northwest wind, no snow expected.

MONDAY: Scattered cloud, freezing level at valley bottom, Above Freezing Layer (AFL) between 1700 m and 2500 m, moderate west/southwest wind, no snow expected.

TUESDAY: Clear skies at dawn, cloud cover increasing to overcast by the afternoon, freezing level at valley bottom, Above Freezing Layer (AFL) between 1500 m and 3000 m, light variable 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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