Avalanche Forecast
Issued: Apr 25th, 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
Buried weak layers are expected to wake up during this warming, it's just a matter of when.
Minimize exposure to avalanche terrain and overhead hazards in the heat of the day. Avoid thin and rocky areas, and sun-affected slopes where warming will be most intense.
Summary
Confidence
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 throughout the 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 are a significant concern 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
Moist surface snow exists on all aspects to mountain top, except north facing high alpine terrain. Warm temperatures and sun will break down any surface crusts that formed overnight. Sun-affected terrain will see the most intense warming, likely creating wet and slushy snow at all elevations.
A series of crusts are buried in the upper snowpack (up to 1m in deeper snowpacks of the Western Purcells, and to 50 cm deep in shallower areas of eastern terrain). These crusts will form ideal sliding layers 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 and limited overnight refreezes are expected to stress these buried weak layers, producing very large avalanches on the basal facet layer. Thin snowpack areas are likely to see the most rapid warming.
At below treeline elevations, the snowpack is thin, melting out, and is moist to ground.
Weather Summary
Tuesday Night
Mostly clear with freezing levels remaining high above 2000 m. Light to moderate westerly winds. No snow expected.
Wednesday
A mix of sun and cloud with freezing levels rising to 2500 m. Treeline temperatures of +8 °C. Moderate to strong westerly winds. Localised areas may see 5 cm of snow/light rain.
Thursday
Full sun with freezing levels up to 2700 m. Treeline temperatures around +10 °C. Light westerly winds.
Friday
Full sun with freezing levels reaching 3500 m. Treeline temperatures near +12 °C. Light westerly winds.
More details can be found in the Mountain Weather Forecast.
Terrain and Travel Advice
- 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.
- Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
- Avoid thin areas like rock outcroppings where you're most likely to trigger avalanches failing on deep weak layers.
Problems
Persistent Slabs
Several crust layers exist in the upper snowpack, avalanche activity on these layers becomes more likely as warming continues to weaken the upper snowpack.
Cornice falls pose a significant threat on their own to backcountry users, and are easy triggers for buried weak layers. Expect cornices to be weak and fragile.
Aspects: All aspects.
Elevations: Alpine, Treeline.
Likelihood
Expected Size
Deep Persistent Slabs
The base of the snowpack remains weak. Large and destructive avalanche activity is expected on this layer as warming continues. Greatest concern is for thin snowpack areas of the Rockies and Purcells.
This is a high-consequence problem as this layer is deeply buried near the ground and avalanches will involve the entire snowpack. Triggering is most likely from thin, rocky start zones and shallow areas with variable snowpack depths. A deep persistent problem often has no warning signs until a large avalanche occurs.
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.
Bear in mind small avalanches like loose wet avalanches have the potential to trigger deeper, larger avalanches.
Aspects: All aspects.
Elevations: All elevations.
Likelihood
Expected Size
Valid until: Apr 26th, 2023 4:00PM
