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.
Up to 10 cm of new snow and strong wind has formed wind slabs that may be reactive to rider triggering. They could be poorly bonded to the underlying snow surfaces, like surface hoar and crusts. Be extra cautious in leeward terrain and convex rolls.
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 90-160 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/ Sunday: Mix of sun and cloud. Freezing levels rise through the day to 1500 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.
Monday: Cloudy with some flurries and strong ridgetop wind from the northwest. Alpine temperatures -3 and freezing levels forecast to drop to 1000 m.
On Friday, explosive triggered wind slabs up to size 2 were reported. Additionally, a natural wind slab cycle up to size 2 was reported but likely from Thursday.
Over the last week, the early December persistent weak layer has produced a few large natural avalanches (2-3) in the center of the region. Explosive controls have also produced a few size 2 avalanches that failed on the same persistent weak layer, one being remotely triggered. These occurred on thin to thick features on northeast-facing slopes from between 1600 m and 2000 m, where the layer was buried 100 cm + deep.
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 10 cm of recent snow and strong winds have formed pockets of reactive wind slab, especially where it sits above surface hoar and crusts.
Around 1900 m and below, a crust is now capping the dense 10-30 cm of snow which has settled significantly with the past mild temperatures. The crust varies from thin to thick, according to the aspect and elevation. Below this, a layer of surface hoar and melt-freeze crusts are found, which seems to be still reactive in isolated areas.
The most notable layer of concern in the snowpack is a crust that was formed in early December and is now down 90-160 cm. This layer was reactive last weekend producing many large size 3 avalanches from all aspects and elevations.
Activity has tapered, however, warming, cornice fall, and human triggers from steep, rocky slopes, with a shallow or thin-to-thick snowpack may wake it up again this weekend.
