Avalanche Forecast
Issued: May 4th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Deep Persistent Slabs, Loose Wet and Cornices.
mconlan,
Avalanche Canada
Intense warming over the past week has destabilized the snowpack, and it may take many days for the snowpack to adjust. Rain switching to snow could produce a variety of avalanche problems. Check out the latest Forecasters' Blog for more information.
Summary
Confidence
Moderate
Avalanche Summary
We've seen widespread wet loose, wet slab, and cornice avalanche releases, of which some has stepped down to buried weak layers, producing very large avalanches. We expect this trend to continue. See here, here, and here for a few examples from the past weekend.
Riders should expect wet loose and slab avalanches and cornice failures during periods of warm air and rain. Avoiding steep slopes when the snow feels sloppy and avoiding cornice exposure are good travel habits.
The likelihood of seeing very large avalanches releasing on a buried weak layer increases with each day of warming. This is particularly true for days without an overnight surface refreeze. Humans are most likely to trigger this layer in steep and rocky slopes where the snowpack is relatively thin.
Snowpack Summary
The snow surface is moist, which is unlikely to freeze overnight. New snow may accumulate in the alpine.
The middle of the snowpack is consolidated with various layers of moist snow, hard snow, and melt-freeze crusts.
A layer of weak faceted grains is found near the base of the snowpack at treeline and alpine elevations.
Cornices are large and looming at this time of year and are weakening with intense warming.
Weather Summary
Rain may switch to snow on Friday for alpine elevations, with a freezing level declining from 3500 m to 2000 m and potentially 10 to 20 cm of snow accumulating. Saturday's freezing level remains near 2000 m with 5 to 10 cm of snow expected in the alpine and rain below. Sunday's freezing level nears 1500 m with 2 to 10 cm of snow forecast.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
- The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
- Use extra caution around cornices: they are large, fragile, and can trigger slabs on slopes below.
- Avoid avalanche terrain during periods of heavy rain.
- Watch for fresh storm slabs building throughout the day.
Problems
Deep Persistent Slabs
The likelihood of very large avalanches releasing on a weak layer buried near the base of the snowpack is increasing with each day of warming. Human triggered avalanches are most likely in steep, shallow, and rocky terrain where the snowpack is relatively thin. Naturally triggered avalanches could occur without warning and are most likely on days when there isn't a good overnight refreeze. Resulting avalanches could travel far and even into snow-free valleys. For this reason, recognizing and avoiding areas with large overhead avalanche slopes, even if they are out of sight, is very important.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
Wet loose and wet slab avalanche activity is expected during periods of rain. Limit your exposure to steep terrain when the snow feels sloppy.
Storm slabs may form in the high alpine where rain may switch to snow.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Cornices
Cornices are large at this time of year and will become more prone to fail as they warm up with spring weather. Stay well back from them when on ridgelines and limit your exposure when travelling on slopes below them, as their release is unpredictable. Remember that a flat spot on a ridgeline could be an overhanging cornice. Cornice falls could trigger very large slab avalanches on slopes below them.
Aspects: North, North East, East, West, North West.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Valid until: May 5th, 2023 4:00PM
