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.
The recent snow accompanied by strong winds and slight warming has formed new and reactive wind slabs. They could have a poor bond to the crusty snow surfaces below. Wind slab avalanches could step down and trigger the deeper persistent slab.
Natural cornice fall is possible with upper elevation warming and solar radiation. Cornice fall could be a hazard on its own and it could trigger a deeper slab avalanche from the slope below.
Loose wet avalanches are possible, especially on southerly aspects and steeper slopes.
The early December crust can be found 100-270 cm deep. A deep persistent slab problem could wake up with forecast warming, solar radiation, cornice fall, and step-downs from smaller avalanches.
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.
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.
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.
