Avalanche Forecast

Archived

Apr 15th, 2023–Apr 16th, 2023

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches possible, human triggered probable.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Below Threshold.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely.

Regions

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

Another warm day is forecast for Sunday with high freezing levels and a chance of rain later in the day. Watch for solar radiation, and then rain, to decrease stability as the day warms up. Pay attention to overhead terrain that may be in the sun at the start of your day. Early starts and finishes are key! Its heading to spring!!!

Confidence

Moderate

Avalanche Summary

One size 2.5 slab avalanche was observed today in the Murray Twins area on a NE aspect at 2400m. This slide occurred in the past 24hrs and overran debris from previous adjacent avalanches.

Snowpack Summary

Dry snow remains on polar aspects at higher elevations, with recently formed wind slabs in lee and cross-loaded terrain. Solar aspects are primarily crusty in the morning and becoming moist with daytime heating and radiation. Travel at lower elevations is fast and easy in the mornings on a thick melt-freeze crust from the rain last week. 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. The deep weak layer of facets and depth hoar have become quite active in the increased heat, and this is expected to continue, with large destructive avalanches possible.

Solar radiation has a big influence on stability at this time of year. Stability will quickly deteriorate on solar aspects as temperatures warm up. These decreases will be most apparent on steep solar aspects, especially in thin rocky terrain. Early starts and finishes that avoid the heat of the day are key. Also pay close attention to what aspect you are on or under, and be mindful of cornices.

Weather Summary

Sunday should be mainly cloudy with a slight chance of flurries/rain in the morning, and more organized precipitation arriving late in the afternoon. Winds will be moderate from the SW, with temperatures climbing to +2C at ridgetop. Freezing levels are expected to be near 2350m, so any precip will fall as rain below this elevation.

More details can be found in the Mountain Weather Forecast.

Terrain and Travel Advice

In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
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.
Cornices become weak with daytime heating or solar exposure.

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.