Date issued

Apr 22, 2018 - 4:00 PM

Valid until

Apr 23, 2018 - 4:00 PM

Prepared by

tim haggarty

Clear skies will bring strong solar heating but likely decent re-freezes Monday and Tuesday mornings. Start early and finish early. A poor recovery, calm winds and high freezing level are likely for Wednesday.

Spring Season Conditions

Avalanche Problem 1: Loose Wet

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

Expect decent freezes for Sunday and Monday evenings to build crusts that will take time for the sun to break down as the day warms up. Start early and finish early to avoid unstable moist snow. Tuesday night's recovery looks a little shaky.

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: Wind Slabs

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

Saturday, 10 cm of snow and strong SW winds formed soft slabs in the alpine that proved to be reactive to skiers in only isolated locations. Buried winds slabs from the previous week may still be present in isolated alpine locations.

Travel and Terrain Advice
  • Be careful with wind loaded pockets, especially near ridge crests and roll-overs.
  • The recent snow may now be hiding windslabs that were easily visible before the snow fell.

Avalanche Problem 3: Persistent Slabs

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

A few avalanches last week were deeper than the most. Some clearly stepped down to the March 15 crust. On shaded aspects events were likely sliding on facets formed at the same interface. This may wake up again with significant heating.

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 Summary

Small soft windslabs were reactive to ski cutting today in isolated locations in the lee of alpine features. Forecasters observed a powder cloud sweep the E face of Fay around 13:00 and suspect a sz 2 cornice or windslab failure. Lots of loose wet avalanche activity on steep solar aspects in the past several days once the sun comes out.

Snowpack Summary

5-10cm of snow with very strong SW winds on Saturday has formed new wind slabs above treeline. Buried temperature crusts exist to 2000m on all aspects and to ridge tops on solar slopes, including the Mar 15 sun crust down 40-70 cm in the alpine. Moist snow at lower elevations, with the entire snowpack becoming moist near valley bottom.

Weather Forecast

Midday clearing Sunday generated moist snow on south aspects despite the cool temperatures. This clearing marks the start of formation of a ridge of high pressure. Expect a 2000m freeze level Monday, 2500m Tuesday (with some significant winds), and 3300m Wednesday (little wind) with strong solar inputs. Models show a poor recovery Tuesday night.

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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