Strong winds and new snowfall will form new wind slabs on Wednesday. If areas receive more than 25cm, a more widespread storm slab may form. Avoid freshly wind-loaded features and use a conservative approach to route selection.
Confidence
Moderate - Timing, track, or intensity of incoming weather system is uncertain
Weather Forecast
A Pacific storm system will bring snowfall to the region starting Tuesday evening. 5-20cm of new snow is expected between Tuesday evening and Wednesday evening with the highest amounts expected in the south of the region. Freezing levels are expected to peak around 1600m and alpine winds should be strong from the southwest. A second storm pulse may result in an additional 5-10cm between Wednesday evening and Thursday evening but one weather model is showing this system missing the region to the south. Freezing levels are expected to fall to around 500m on Thursday and winds should be light from the northwest after the storm ends. On Friday, a ridge of high pressure should result in dry, sunny conditions with light alpine winds and cooling temperatures.
Avalanche Summary
On Tuesday, the Avalanche Canada field team was reporting old natural wind slab avalanches in the north of the region which had likely released sometime over the weekend. On Sunday, ski cutting was producing 5-10cm wind slabs on steep rolls below treeline in the south of the region. Explosives control on Saturday triggered a size 1 wind slab in the south of the region.
Snowpack Summary
The Avalanche Canada field team has been finding variable conditions across the region which will now be buried by the new snowfall. East of Crownest Pass the snow surface has been widely wind affected. Extensive scouring has been reported in some areas and and stiff wind slabs exist in lee features at treeline and in the alpine. In areas that have seen less extreme wind, recently formed wind slabs are likely softer, deeper, and may overlie surface hoar, facets, and/or a sun crust which formed at the start of January. In either case, snow pit tests in wind loaded features show recently developed slabs are failing under moderate loads and can propagate over wide distances. The early December crust can be found down around 60-90cm. It is not currently expected to pose an avalanche problem but could wake-up in the future with substantial warming or heavy snow loading.
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.