Avalanche Forecast

Purcells

Date issued

Dec 5, 2017 - 4:59 PM

Valid until

Dec 6, 2017 - 2:00 PM

Prepared by

shorton

One more day of cool weather before alpine temperatures soar. Watch for wind slabs on Wednesday and avoid slopes getting hit by the sun.

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

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.

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?

Fresh wind slabs have been forming throughout the week, so be careful around ridges and gullies. Solar warming may make slabs extra reactive on south-facing slopes.

Travel and Terrain Advice
  • Travel on ridgetops to avoid wind slabs on slopes below.
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • Avoid sun exposed slopes when the solar radiation is strong, especially if snow is moist or wet.

Avalanche Summary

Limited reports from the region over the past few days show a pattern of touchy wind slabs around alpine ridges. On Tuesday, a size 1.5 wind slab was triggered by a skier on a south-facing slope at 2600 m in the Invermere area. A Mountain Information Network (MIN) report describes multiple size 1 wind slabs triggered by ski cutting from the Golden area 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

WEDNESDAY: Sunny with valley cloud in the morning, light northwest wind, inversion forming with alpine temperatures reaching -4 C.

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

FRIDAY: Sunny with valley cloud, light wind, inversion with freezing level up to 2700 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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