Date issued

Apr 27, 2018 - 4:00 PM

Valid until

Apr 28, 2018 - 4:00 PM

Prepared by

tim haggarty

Expect a modest recovery and strong daytime heating again on Saturday before the clouds roll in. Early morning rain is possible Sunday and will likely contribute to a poor recovery at lower elevations before cooling leads to snowfall later in the day

Spring Season Conditions

Avalanche Problem 1: Loose Wet

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

Loose wet avalanches have been common over the last couple of days and will continue Saturday until cooling takes over Sunday. Starting and ending very early are the best defense. Even small wet slides are very powerful and destructive.

Travel and Terrain Advice
  • Use extra caution on slopes if the snow is moist or wet.
  • Watch for clues, like sluffing off of cliffs, that the snowpack is warming up.

Avalanche Problem 2: Wet Slabs

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

As the upper layers of the snowpack are becoming moist persistent weak layers are failing as wet slabs. Most of these events are limited to shallow crusts on solar aspects however some slopes have seen enough heating to allow releases on older layers

Travel and Terrain Advice
  • Pay attention to overhead hazards like cornices which could easily trigger persistent slabs.
  • Avoid shallow snowpack areas where triggering is more likely.

Avalanche Problem 3: Cornices

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

Cornice failures are occurring on a regular basis now with warm temperatures and intense solar inputs. These large triggers have caused failures on the persistent weak layers deeper in the snow pack over the last couple days.

Travel and Terrain Advice
  • Cornices become weak with daytime heating, so travel early on exposed slopes.
  • Minimize exposure to overhead hazard from cornices.

Avalanche Summary

Ongoing wet snow avalanches typical for this time of year are occurring with daytime heating. Both loose snow and wet slabs are common with slabs occasionally stepping down to mid-pack and basal layers. These vary by aspect and elevation but can travel far as they entrain isothermal snow. Many events have reached full path over the last two days.

Snowpack Summary

Crust or moist snow on all solar aspects depending on temperatures. Buried temperature crusts to 2000m on all aspects and to ridge top on solar slopes, including the Mar 15 crust down 40-70 cm in the alpine. Moist snow at lower elevations, with the entire snowpack becoming moist below treeline in the afternoons.

Weather Forecast

Temperatures have been slightly inverted with better freezes at valley bottom, but temperatures will stay above freezing in the alpine Friday evening. Saturday will see solar heating progress quickly with clear skies until midday when winds pick up and bring cloud later in the day.  Sunday morning may bring rain below 2000m turning to snow by noon

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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