Avalanche Forecast

Archived

Apr 19th, 2023–Apr 21st, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

Kananaskis, Bow Valley, Highwood Pass, North 40, Spray - KLakes.

Convective flurries continue to bring snow to the region with some areas seeing up to 30cm (Aster/Mt Joffre area). Ski quality is good on planar slopes where you are sliding on top of the crust. Any slope that has not yet released should be treated as suspect. Soon we will hopefully be into a good melt freeze spring cycle!!!

Confidence

High

Avalanche Summary

Numerous loose dry avalanches up to sz 1.5 were observed on all aspects. No new slab avalanche activity was noted but visibility was very limited throughout the day.

Snowpack Summary

Up to 20cm of new snow via convective flurries was seen in the Commonwealth area Wednesday at treeline. Winds were generally calm so there was little in the way of new windslabs developing. The new snow was sluffing easily from steep terrain and in areas where it was overlying the previous melt freeze/rain crust so be aware of the potential for loose dry avalanches to run far and fast. Moist snow was encountered in valley floors by 1100am so continue to start early!Forecasters continue to track persistent weaknesses down anywhere from 40 to 100cm on polar aspects. These weaknesses are highly variable in nature and travelers should take the time to dig down and evaluate the snowpack frequently. Also, the lingering deep persistent slab problem is still alive and well.

If the sun comes out stability will deteriorate quickly so pay attention to the incoming radiation on aspects you are travelling on or under. Early starts and finishes are a great way to deal with some of these issues.

Weather Summary

A murky next few days with convective flurries being the norm for the region. Storms pass over and within a few mins 3-5cm of snow can fall followed by blue sky. This is common in spring and snowfall amounts can vary even by drainage. Winds over the next 24hrs are still in the light range out of the W-NW with overnight lows around -10C. When cloudy conditions persist overnight lows may not be as cold as has been forecast so use the weather stations for the region to assess quality of freeze. If the sun comes out, it quickly packs a punch and moist snow develops in minutes. The intense solar radiation can also decrease stability on solar aspects so keep a close eye on aspect and weather. Lots of weather changes in spring!!!!

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

Watch for newly formed and reactive wind slabs as you transition into wind affected terrain.
Avoid steep slopes when air temperatures are warm, or solar radiation is strong.
In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.

Problems

Wind Slabs

Wind Slab avalanches are the release of a cohesive layer of snow (a slab) formed by the wind. Wind typically transports snow from the upwind sides of terrain features and deposits snow on the downwind side. Wind slabs are often smooth and rounded and sometimes sound hollow, and can range from soft to hard. Wind slabs that form over a persistent weak layer (surface hoar, depth hoar, or near-surface facets) may be termed Persistent Slabs or may develop into Persistent Slabs.

Persistent Slabs

Persistent Slab avalanches are the release of a cohesive layer of snow (a slab) in the middle to upper snowpack, when the bond to an underlying persistent weak layer breaks. Persistent layers include: surface hoar, depth hoar, near-surface facets, or faceted snow. Persistent weak layers can continue to produce avalanches for days, weeks or even months, making them especially dangerous and tricky. As additional snow and wind events build a thicker slab on top of the persistent weak layer, this avalanche problem may develop into a Deep Persistent Slab.

Deep Persistent Slabs

Deep Persistent Slab avalanches are the release of a thick cohesive layer of hard snow (a slab), when the bond breaks between the slab and an underlying persistent weak layer deep in the snowpack. The most common persistent weak layers involved in deep, persistent slabs are depth hoar or facets surrounding a deeply buried crust. Deep Persistent Slabs are typically hard to trigger, are very destructive and dangerous due to the large mass of snow involved, and can persist for months once developed. They are often triggered from areas where the snow is shallow and weak, and are particularly difficult to forecast for and manage.