Avalanche Forecast

Northwest Inland

Date issued

Dec 16, 2017 - 5:10 PM

Valid until

Dec 17, 2017 - 2:00 PM

Prepared by

ghelgeson

Plan to avoid potentially wind loaded slopes just below ridge crest and areas with a thin or variable snowpack, especially if you are traveling in the alpine.

Regular season
Saturday - December 16, 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

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 - December 17, 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

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.

Monday - December 18, 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

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: Wind Slabs

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

These wind slabs are most likely to be found immediately lee of ridge crest and around mid-slope terrain features like rock outcroppings. While relatively small, these could be problematic in complex terrain.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • Avoid steep convexities or areas with a thin or variable snowpack.

Avalanche Problem 2: Deep Persistent Slabs

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

The late October crust lies near the base of the snowpack with a thin layer of weak, sugary snow above it. This layer should be gaining strength, but a heavy trigger in a thin snowpack area could initiate a failure and subsequent large avalanche.

Travel and Terrain Advice
  • Be especially cautious in shallow snowpack areas where triggering a deeper layer may be easier.
  • Be aware of the possibility for full depth avalanches due to deeply buried weak layers.

Avalanche Summary

No recent avalanche observations.

Please submit your information to the Mountain Information Network.

Snowpack Summary

5cm of new snow fell Friday night into Saturday accompanied by moderate to strong southwest wind. This new snow rests on a wide variety of old surfaces including solar and temperature crusts on sun-exposed slopes and stiff, stubborn wind slabs in leeward alpine terrain. Feathery surface hoar and surface facets previously formed below treeline from valley bottom up to around 1500m.

Approximately 30 to 50cm of snow sits on two crusts that were buried near the end of November. These crusts are widespread and extend into the alpine. Although snowpack tests have previously shown hard results at these crust interfaces, more recent observations have been limited. Below these crusts, a well settled mid-pack overlies the late October crust near the base of the snowpack. This "crust/facet combo" layer is widespread and has not been reactive to rider and remote triggers since the end of November. These rain crusts will likely be with us all winter but may not pose a problem until we see a significant change in the weather.

Average snowpack depths now total 80-140 cm at treeline elevations and up to 160 cm in the alpine.

Weather Forecast

A frontal system is currently impacting the coast, and some spill over into the Inland region is probable. Light precipitation and strong southwest wind is expected through Saturday night. Snow and wind, albeit modest in quantity, is expected on Sunday and Monday before the ridge rebounds on Tuesday giving way to a cool dry pattern.

SATURDAY NIGHT: Freezing level falling from 1400m down to around 600m through the night. 5 to 10cm of snow possible, strong to extreme southwest wind.

SUNDAY: Broken cloud cover, freezing level around 500m, moderate to strong west/southwest wind, trace to 5cm of snow possible.

MONDAY: Scattered cloud cover, freezing level near valley bottom, moderate to strong southwest wind, trace to 5cm of snow possible.

TUESDAY: Scattered cloud cover, freezing level at valley bottom, light variable wind, no new snow expected.

Visit avalanche.ca/weather for a more detailed mountain weather forecast.

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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