Avalanche Forecast

Archived

Jan 22nd, 2022–Jan 23rd, 2022

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Alpine

Natural avalanches unlikely, human triggered possible.

Treeline

Natural avalanches unlikely, human triggered possible.

Below Treeline

Natural avalanches unlikely, human triggered possible.

Regions

Lizard-Flathead.

Choose simple terrain, and avoid large features, especially if the weather is feeling warm and sunny. Conservative decision making is a good defence against a complicated snowpack and uncertain weather. Check out our recent forecasters' blog for more details.

Confidence

Moderate - Uncertainty is due to the timing or intensity of solar radiation and its effect on the snowpack. Uncertainty is due to difficult to forecast freezing levels. The snowpack structure is generally well understood.

Weather Forecast

A ridge of high pressure brings warming and sunny skies through the weekend. Alpine inversions may see temperatures as high as +1 degrees with valley bottoms seeing some cloud and cooler air pooling at the lower elevations.

Saturday Night: Mostly cloudy. Freezing levels fall to 500 m but alpine temperatures near +1 C with possible above freezing layer (AFL). Valley cloud and cooler temperatures down low. Ridgetop winds moderate from the northwest.

Sunday: Mix of sun and cloud. No new snow expected. AFL breaking down. Freezing levels rising to around 1000 m. Strong northwest ridge wind.

Monday: Mostly cloudy. Possible trace of snow expected. Moderate ridge wind, northwest through northeast. Freezing levels drop to 250 m overnight, rise to 900 m by the afternoon.

Tuesday: Partly cloudy. No new snow expected. Strong northwest ridge wind. Freezing levels drop to valley bottom overnight, rise back to 900 m by the afternoon.

Avalanche Summary

Most concerning is the warm weather this weekend. Warming, solar radiation, smaller surfaces avalanches, and cornice fall could trigger deep persistent slabs.

On Friday, several wind slabs and storm slabs up to size 2 were reported. A natural cornice fall also occurred pulling a size 1.5-2 storm slab in the fans on the slope.

Snowpack Summary

Incoming warm air may ride on top of colder air in the valleys, so the snowpack may experience above zero temperatures at higher elevations, where you may not expect them. If this warming occurs and the sun comes out, the alpine snowpack could experience some rapid change for the worse.

Up to 15 cm of new storm snow fell Thursday with fairly light winds. Moderate to strong winds from the southwest on Friday formed fresh and reactive wind slabs. Wind slabs may be more reactive where they sit above older wind-affected and crusty surfaces. Around 2200 m and below, a crust caps the dense 15 to 30 cm of snow which has settled significantly with the past mild temperatures. The crust varies with aspect and elevation from thin (2 cm thick) in the alpine to (4 cm) thick below treeline. Below this, the midpack is well consolidated above the early December crust/ facet interface.

The most notable layer of concern in the snowpack is a widespread crust that was formed in early December and is now down 100-270 cm. With warming last week this deep persistent slab problem woke up and produced several very large avalanches. The forecast warm weather and sunshine this weekend is concerning and we could see this avalanche problem wake up yet again. Warming, solar radiation, and cornice fall could all play a role in triggering deep persistent slabs.

Terrain and Travel

In areas where deep persistent slabs may exist, avoid shallow or variable depth snowpacks and unsupported terrain features.
Minimize overhead exposure; avalanches triggered by warming or cornice fall may be large and destructive.
Wind slabs may be poorly bonded to the underlying crust.
A moist or wet snow surface, pinwheeling and natural avalanches are all indicators of a weakening snowpack.
In times of uncertainty conservative terrain choices are our best defense.

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.

Cornices

Cornice Fall is the release of an overhanging mass of snow that forms as the wind moves snow over a sharp terrain feature, such as a ridge, and deposits snow on the downwind (leeward) side. Cornices range in size from small wind drifts of soft snow to large overhangs of hard snow that are 30 feet (10 meters) or taller. They can break off the terrain suddenly and pull back onto the ridge top and catch people by surprise even on the flat ground above the slope. Even small cornices can have enough mass to be destructive and deadly. Cornice Fall can entrain loose surface snow or trigger slab avalanches.

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.