Strong wind and recent snow have formed reactive wind slabs.
Warm temperatures, weak cornices combined with a lingering deep persistent slab problem may equal large and destructive avalanches. Its a good time to approach the mountains cautiously and even expect surprises.
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: Mix of sun and cloud. Freezing levels rise through the day to 2000-2500 m with generally clear skies. Alpine temperatures near +1 C. Possible inversion may hold valley cloud and cooler temperatures down low. Ridgetop winds moderate from the northwest. Expect cooling overnight.
Sunday: Mix of sun and cloud with freezing levels hovering around 2000 m. Strong northwest wind.
Monday: Cloudy with some flurries and strong ridgetop wind. Alpine temperatures -3 and freezing levels forecast to drop to 1000 m.
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.
Wind slabs may continue to be reactive on Saturday, especially where they have a poor bond to the underlying crust.
Most concerning is the warm weather this weekend. Warming, solar radiation, smaller surfaces avalanches, and cornice fall could trigger deep persistent slabs. This layer has been dormant but to no surprise could wake up.
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.
