Regions
Kootenay Boundary.
Confidence
Fair - Forecast snowfall amounts are uncertain on Tuesday
Weather Forecast
The weak ridge that brought cooler and drier conditions on Saturday is expected to be pushed out of the region by Sunday morning. Warm moist air should bring cloud and rising freezing levels to about 1000 metres on Sunday. The winds are expected to build from the southwest on Monday, and moderate precipitation should start to accumulate snow by late afternoon. A trailing cold front is forecast for Tuesday. Snowfall amounts are un-certain and will depend on how much moisture is in the area when the cooler air arrives.
Avalanche Summary
Reports of natural avalanches are getting less frequent, but reports of remotely triggered and easily triggered avalanches have increased. The average size of reported avalanches has dropped closer to 2.0 from the recent observations of 3.0 I think this trend of slight improvement is short-lived. The recent natural avalanche cycle produced natural and human triggered avalanches up to size 3.0. These occurred on all aspects above 1700m with wide propagations, and crown depths up to 80cms. Many of these are failing on the mid-December surface hoar, mostly on north through east aspects from 1500m to the peaks. A skier remotely triggered an avalanche from 50m away and in many places shooting cracks and whumphing are further indicators of a very touchy, unstable snowpack.
Snowpack Summary
There is now 50-80 cm above the mid-december weak layer of surface hoar. The wind has been strong at times during the recent storms, and has built stiff wind-slabs in the alpine and at treeline on North, East and in some locations South aspects. Warm temperatures have developed a soft slab in the storm snow in areas that were not affected by the wind. The surface hoar layer continues to provide easy and sudden shears in tests. The mid-pack is generally well settled. Facets at the base of the snowpack have not been reactive recently.
Problems
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.
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.