Date issued

Feb 4, 2018 - 8:02 AM

Valid until

Feb 5, 2018 - 8:00 AM

Prepared by

mark herbison

Allow the snowpack time to adjust to the recent snow load. Avoid overhead hazard or spending anytime in runout zones as large avalanches have been running into valley bottoms.

Regular season
Saturday - February 3, 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.

Sunday - February 4, 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.

Monday - February 5, 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?

Consistent snowfall has created a storm slab. Previous strong South winds have redistributed the new snow into a windslab in the Alpine and at Treeline. If triggered, the slab could step down to deeper persistent weak layers.

Travel and Terrain Advice
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • If triggered the storm slabs may step down to deeper layers resulting in large avalanches.

Avalanche Problem 2: Persistent Slabs

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

Natural avalanche activity on the persistent weak layers has tapered off recently. The Jan 16th, 4th and Dec 15th surface hoar layers are buried deep, but avalanches in the storm snow can step down and trigger these weak interfaces.

Travel and Terrain Advice
  • Pay attention to overhead hazards like cornices which could easily trigger the deep persistent slab.
  • Minimize overhead exposure; avalanches may reach the end of run out zones.

Avalanche Summary

Several avalanches reported yesterday from backcountry users, some of which buried regular skin track routes. Heavy snowfall and winds produced natural avalanches to size 3.0.

Artillery avalanche control produced numerous avalanches, size 2.0-3.5, with several avalanches dusting the highway.

Snowpack Summary

25cm in 24hrs brings the weekly snowfall total to ~150cm creating a healthy sized storm slab. Previous moderate to strong south winds have created pockets of windslab in the alpine. A meter and a half of settling snow sits over the Jan 16th surface hoar layer, which is the uppermost PWL and is still distinct and easy to pick out on pit walls.

Weather Forecast

Winter is great, especially when it snows a lot! Today we can expect to see another 5-10cm of it, giving us poor visibility in the alpine. Temps will range from -5 to -10 with 20km/hr ridgetop winds from the southwest. The next weather system will arrive Tuesday evening and continue into Thursday with forecasted snowfall amounts over 50cm.

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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