Avalanche Forecast

Purcells

Date issued

Dec 4, 2017 - 4:27 PM

Valid until

Dec 5, 2017 - 2:00 PM

Prepared by

shorton

Fresh wind slabs are likely at higher elevations. Evaluate the snow and terrain carefully as there is still limited information from this region.

Regular season
Tuesday - December 5, 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.

Wednesday - December 6, 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.

Thursday - December 7, 2017
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

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?

Wind slabs are most likely on the downwind side of ridges and gullies. Changes in wind direction may form fresh wind slabs this week.

Travel and Terrain Advice
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Travel on ridgetops to avoid wind slabs on slopes below.

Avalanche Summary

A Mountain Information Network (MIN) report from the Golden area describes multiple size 1 wind slabs produced by ski cutting on Sunday. Several size 1 wind slabs were also triggered by explosives near ridge crests throughout the region over the weekend.

Snowpack Summary

Snow from last week's storms is settling and getting redistributed into fresh wind slabs by northwest winds. Roughly 20-40 cm of recent snow sits above various crusts from the warm weather in late November. Two deeper layers may be found in the snowpack, including the November 10 surface hoar and the Halloween crust (80 to 100 cm deep). The late November crust is the most likely of these layers to develop into a problem in the future. Snow depths decrease rapidly below treeline, where the primary hazards are rocks, stumps, and open creeks.

Weather Forecast

TUESDAY: Alpine sun and valley cloud, light wind, alpine temperatures around -7 C.

WEDNESDAY: Sunny with valley cloud, light wind, inversion forming with alpine temperatures possibly reaching above 0 C.

THURSDAY: Sunny with valley cloud, light wind, inversion with freezing level up to 3000 m.

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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