Avalanche Forecast

Northwest Inland

Date issued

Dec 17, 2017 - 5:24 PM

Valid until

Dec 18, 2017 - 2:00 PM

Prepared by

ghelgeson

Travel with intention so that you avoid potentially wind loaded slopes just below ridge crest as well as thin rocky alpine features, where it may still be possible to trigger old deeply buried weaknesses.

Regular season
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.

Tuesday - December 19, 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

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: 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
  • Avoid steep convexities or areas with a thin or variable snowpack.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Use ridges or ribs to avoid pockets of wind loaded snow.

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 and while it should be gaining strength, a heavy trigger in a thin rocky terrain feature may still be able to initiate a failure and subsequent large avalanche.

Travel and Terrain Advice
  • Be aware of the possibility for full depth avalanches due to deeply buried weak layers.
  • Be especially cautious in shallow snowpack areas, it may be possible to trigger large avalanches.

Avalanche Summary

No recent avalanche observations. 

Please submit your information to the Mountain Information Network.

Snowpack Summary

The inland region picked up 5 to 15cm of new snow over the weekend accompanied by wind that was largely out of the west, but there were periods of southeast wind recorded too.  This new snow rests on a wide variety of old surfaces including small facets, crusts on solar aspects and stubborn old wind slabs near ridge crest.  In protected areas below 1500m the new snow may be sitting on previously formed feathery surface hoar.

Two crusts formed near the end of November are found approximately 30 to 50cm below the surface.  These crusts are widespread and extend into the alpine.  Previous snowpack tests produced hard results on these crusts, but we have not seen any recent information about their sensitivity to triggering.  Below these crusts, a well settled mid-pack overlies the late October crust which is down near the ground.  The October crust is widespread and has not been reactive to human triggering since the end of November.

Average snowpack depths in the region are between 80 and 140cm at treeline, with up to 160cm in the alpine.

Weather Forecast

The Northwest Inland is expected to be relatively cool and dry for the forecast period as a more zonal pattern favors the regions along the 49th parallel. A trace of snow is possible on Monday before yet another ridge takes over for the foreseeable future.

MONDAY: Scattered cloud cover, freezing level at valley bottom, moderate west wind, trace of snow possible.

TUESDAY: Clouds clearing through the day, freezing level at valley bottom, light variable wind, no new snow expected.

WEDNESDAY: A few clouds, freezing level at valley bottom, strong to extreme northwest wind, no new 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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