Avalanche Forecast

South Coast

Date issued

Nov 25, 2017 - 3:58 PM

Valid until

Nov 26, 2017 - 2:00 PM

Prepared by

mgrist

Wet, warm weather forecasted for Sunday means the potential for loose, wet avalanches in extreme terrain. Watch for pockets of storm slab in areas that receive snow instead of rain. Very strong winds are forecast Sunday morning at higher elevations.

Regular season
Saturday - November 25, 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

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.

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 - November 26, 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

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.

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 - November 27, 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: Loose Wet

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

Rain has saturated the upper snowpack and the potential for loose wet avalanches exists on steep, unsupported terrain features. Even a small loose wet avalanche can gain enough mass to become a big problem.

Travel and Terrain Advice
  • Be cautious of wet sloughs in steep terrain, particularly where the debris flows into terrain traps.

Avalanche Problem 2: Storm Slabs

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

Be aware that storm slabs may exist in the high alpine. Dial back your terrain selection if you find the snow surface changing from wet snow to new snow as you gain elevation.

Travel and Terrain Advice
  • Use extra caution in lee areas in the alpine. Storm snow may be forming touchy slabs.
  • Be alert to conditions that change with elevation.

Avalanche Summary

No recent avalanches have been reported. However, the recent rain-on-snow event is suspected to have caused a natural, loose wet avalanche cycle.

Although natural avalanche activity and human triggering potential has decreased with cooler temperatures, ongoing rain will maintain the potential for loose wet avalanches, particularly in steep, unsupported terrain. Storm slab development is also a concern at high alpine elevations where precipitation may fall as snow accompanied with strong winds.

Snowpack Summary

There is little information on snowpack structure at this time, except that recent heavy rainfall has saturated the upper snowpack at all elevations and washed away much of the snow at lower elevations. Travel below treeline is becoming more and more rugged, with many open creeks and early season hazards. 

Up to 30 cm of heavy wet snow may have fallen at the highest elevations (above 1400m) Friday into Saturday.

Snow depth varies from 40 - 130 cm for elevations between 900 - 1200m across the region.

Weather Forecast

Another warm and wet system will pummel the South Coast on Sunday before freezing levels drop with moderate snow accumulations into early next week.

Sunday: Rain during the day (20-30 mm) before the freezing levels drop to 1000m (and possibly as low as 700m) in the evening with 10-15cm snow overnight. Strong to extreme south winds at ridgetop on Sunday morning.

Monday: Flurries, accumulation 10-15 cm. Light to moderate southwest wind. Alpine temperature -1. Freezing level 1000 m.

Tuesday: Snow, accumulation 20-30 cm. Moderate to strong south wind. Alpine temperature -1. Freezing level 1200m.

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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