Avalanche Forecast

Northwest Inland

Date issued

Feb 7, 2018 - 4:59 PM

Valid until

Feb 8, 2018 - 2:00 PM

Prepared by

jmcbride

New snow and wind are loading several buried weak layers in the snowpack. Conservative terrain, avoiding wind affected areas and minimizing exposure to overhead hazard are good choices. The potential for large avalanches to run long distances exists.

Regular season
Wednesday - February 7, 2018
Alpine

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.

Treeline

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.

Below Treeline

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.

Thursday - February 8, 2018
Alpine

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.

Treeline

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.

Below Treeline

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.

Friday - February 9, 2018
Alpine

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.

Treeline

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.

Below Treeline

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.

Avalanche Problem 1: Storm Slabs

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

Wednesday's storm will likely form new storm slabs particularly at upper elevations and in wind-exposed areas. These slabs may be reactive to human triggering and a release may have the potential to step-down to a deeper layer buried in the snowpack.

Travel and Terrain Advice
  • Watch for whumpfing, hollow sounds, shooting cracks or recent avalanches.
  • Avoid lee and cross-loaded terrain near ridge crests or convex rolls.

Avalanche Problem 2: Persistent Slabs

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

There is limited information about weak layers buried 80-120 cm below the surface. They produced a few large avalanches last week, and may remain sensitive to human triggering in shallow snowpack areas.

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

Avalanche Summary

On Monday evidence of a natural avalanche cycle from size 1.5-2.5 was reported on north through south aspects between 1200-1600 m in the Howson Range failing both in the recent storm snow as well as the deeper mid-December layer. A natural size 2.5 that failed on a deep weak layer of sugary, facets at the base of the snowpack was also reported from the northern part of the region near Ningunsaw.

On Saturday a small storm slab was reportedly human triggered on an east facing aspect around 1000 m. And at the start of the storm on Wednesday and Thursday skiers triggered a few small slabs on steep convex rolls.

Last week some large (size 2-3) natural persistent slab avalanches in the Howsons, and two large (size 2.5) remotely triggered avalanches north of Kispiox were reported. We have no information from the Smithers area, but suspect a similar deeper weakness could exist there too. Activity on buried weak layers is most suspect during periods of heavy loading or rapid warming, hence it's time to be cautious.

Snowpack Summary

Wednesday's storm delivered about 15 cm of new snow during the day bringing storm snow totals to 40-80 cm since last Thursday which has mostly formed well settled upper snowpack layers.

A crust and/or weak feathery surface hoar layer buried in mid-January now lies 50-90 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 treeline elevations.

Another two crust / surface hoar layers that were buried in December are now 90-130 cm below the surface. These layers produced sudden results in recent snowpack tests and have been the suspected weak layer in recent large remotely (from a distance) triggered avalanches.

Weather Forecast

TONIGHT: Flurries. Accumulation 5-10 cm. Ridge wind light, east. Temperature -14. Freezing level valley bottom.

THURSDAY: Mostly cloudy, light flurries. Accumulation 2-5 cm. Ridge wind light, northeast. Temperature -14. Freezing level valley bottom.

FRIDAY: Sunny. Ridge wind light, northeast. Temperature -10. Freezing level valley bottom.

SATURDAY: Mostly sunny. Ridge wind light to moderate, southwest. Temperature -6. 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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