Avalanche Forecast
Issued: Apr 24th, 2023 4:00PM
The alpine rating is , the treeline rating is , and the below treeline rating is Known problems include Persistent Slabs, Deep Persistent Slabs and Loose Wet.
wlewis,
Avalanche Canada
Warm temperatures and sunshine continue to stress an already fragile snowpack. Persistent and deep persistent slab avalanche activity will become more likely as temperatures climb this week.
Minimize your exposure to avalanche terrain in the heat of the day. Avoid thin and rocky areas on sun-affected slopes.
Summary
Confidence
Moderate
Avalanche Summary
Observations are very limited at this time of year, please consider sharing any information or photos you have on the Mountain Information Network to help guide our forecasts.
Loose wet avalanches were observed this week, naturally triggered by the sun and warm temperatures. Natural activity is expected to continue this week with an increased likelihood of deep avalanche releases as warming continues.
The numerous buried weak layers including the basal facets remain a concern, especially with rising freezing levels. Recent avalanche activity on these layers in adjacent forecast areas highlights the need to avoid rocky and thin snowpack areas for the remainder of the season.
A fatal size 3 occurred near Lake Louise on April 22nd on the basal facets, in a particularly thin and rocky area with a 50 cm deep snowpack. All information can be found here.
Snowpack Summary
Warm temperatures will weaken the surface snow as freezing levels rise on Tuesday, breaking down surface crusts and moistening any previously dry snow to around 2000 m on all aspects. Sun-affected terrain will see the most intense warming, likely creating wet and slushy snow to mountain top.
Recent wind-affected storm snow then sits over a variety of crust, surface hoar, and/or facet layers buried from mid-March through early April. Crusts form an ideal sliding layer for avalanche activity as warming affects the snowpack.
The mid snowpack is generally settled and strong. However, the lower snowpack includes a widespread layer of large, weak facets and/or depth hoar crystals. This weak layer has been responsible for several very large and destructive avalanches throughout the season.
Continued warm temperatures this week are expected to stress these buried weak layers, making them more sensitive to triggers. We are concerned about the potential for very large avalanches on the basal facet layer as temperatures remain warm overnight, limiting recovery within the snowpack.
Weather Summary
Monday Night
Cloud begins to clear. Light to moderate westerly wind. Freezing levels drop to 1500 m. No snowfall expected.
Tuesday
Mostly sunny with freezing levels rising to 2200 m. Treeline temperatures around +5 °C. Moderate westerly winds. No snowfall.
Wednesday
A mix of sun and cloud with freezing levels rising to 2500 m. Treeline temperatures of +8 °C. Moderate westerly winds. Localised areas may see 5 cm of snow/light rain.
Thursday
Full sun with freezing levels heading towards 3000 m. Treeline temperatures above +8 °C. Light westerly winds.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
- The more the snowpack warms-up and weakens, the more conservative you`ll want to be with your terrain selection.
- The likelihood of deep persistent slab avalanches will increase with each day of warm weather.
- Cornices become weak with daytime heating or solar exposure.
Problems
Persistent Slabs
Several crust layers exist in the upper snowpack, avalanche activity on these layers becomes more likely as warming continues.
Use extra caution around ridgelines and on convex slopes. Retreat to mellower terrain (think low angle, low exposure) if you find signs of instability like shooting cracks, whumpfs, or recent avalanches.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
The base of the snowpack remains very weak. Deep persistent slab avalanches continue to be reported in this area and adjacent forecast areas with similar snowpack structures.
This is a low-probability/high-consequence avalanche problem as this layer is deeply buried near the ground. Avoid thin, rocky start zones and shallow areas with variable snowpack depths.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Loose Wet
Avoid slopes that have moist or wet surface snow in the afternoon when warming is expected to be most intense. Warming will be amplified on steep, sun-affected slopes around rocky outcrops.
Stick to shaded slopes earlier in the day if you choose to venture out, and head out of the backcountry before peak warming.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Apr 25th, 2023 4:00PM
