Avalanche Forecast

Northwest Inland

Date issued

Feb 17, 2018 - 4:14 PM

Valid until

Feb 18, 2018 - 2:00 PM

Prepared by

jmcbride

Watch for areas where reactive wind slabs may still be lingering. And keep in mind that it may still be possible to trigger a deeper weak layer, especially in thin or shallow areas.

Regular season
Saturday - February 17, 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.

Sunday - February 18, 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.

Monday - February 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.

Avalanche Problem 1: Wind Slabs

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

Winds have formed stiff wind slabs in exposed areas at tree line and above. These slabs may still be reactive to human triggering. Also a release near the surface may step-down to a deeper layer buried in the snowpack.

Travel and Terrain Advice
  • Be cautious as you transition into wind affected terrain.
  • Avoid lee and cross-loaded terrain near ridge crests or convex rolls.
  • Watch for whumpfing, hollow sounds, or shooting cracks.

Avalanche Problem 2: Persistent Slabs

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

Weak layers buried 100-150 cm below the surface have been reactive in snowpack tests and have also produced a few large avalanches recently. These layers may also remain sensitive to human triggering in shallow snowpack areas.

Travel and Terrain Advice
  • Avoid lingering in runout zones, avalanches triggered from above may run long distances.
  • Avoid shallow or thick to thin snowpack areas where triggering a deeper layer is more likely.

Avalanche Summary

There have been no new reports of avalanches since Wednesday when widespread natural avalanche activity up to size 2.5 was reported on wind-loaded leeward, slopes as well as loose snow releases on steep solar aspects in the afternoon.

Avalanche activity will likely taper off with a period of cold, clear weather expected to persist well into the week. Watch for areas where reactive windslabs may still linger, and be extra cautious near thin spots and shallow snow pack areas where triggering a deeper weak layer is more likely.

Snowpack Summary

Winds (mostly northwesterly) have scoured wind-exposed slopes and created stiff wind slabs on leeward slopes at tree line and above. In areas sheltered from the wind, you can still find 30-50 cm of settled storm snow.

A crust and/or weak feathery surface hoar layer buried in mid-January now lies about 100 cm below the surface. The crust exists well into the alpine and the surface hoar can be found in sheltered areas in the lower alpine and tree line elevations. Snowpack tests produced hard, sudden results on weak, sugary snow crystals associated with this crust in the Smithers area, indicating that this is still a layer of concern to watch for.

Another two crust / surface hoar layers that were buried in December are now 100-150 cm below the surface and may still be sensitive to triggering from shallow snowpack areas.

Weather Forecast

SUNDAY: Mostly sunny. Ridge wind, moderate, northeast. Temperature -15. Freezing level valley bottom.

MONDAY: Mostly sunny. Ridge wind light to moderate, northwest. Temperature -10. Freezing level valley bottom.

TUESDAY: Mostly sunny. Ridge wind light, northwest. Temperature -8. Freezing level valley bottom.

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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